AI Trajectory

null

{
  "EnableConfigs": [
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "arch_bpf_timed_may_goto",
    "bpf_jit_supports_timed_may_goto"
  ],
  "Reasoning": "The patch implements architecture-specific support for the BPF timed may_goto loop bound on RISC-V 64-bit. It adds the arch_bpf_timed_may_goto assembly trampoline and enables it in the JIT compiler. This is functional code reachable by loading BPF programs with may_goto instructions on RISC-V.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 44763c9bdfb67d695f6a41961d1b194aa3e93334\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Tue Jul 14 08:02:21 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/arch/riscv/net/Makefile b/arch/riscv/net/Makefile\nindex 9a1e5f0a94e559..6458d4d51990a7 100644\n--- a/arch/riscv/net/Makefile\n+++ b/arch/riscv/net/Makefile\n@@ -3,7 +3,7 @@\n obj-$(CONFIG_BPF_JIT) += bpf_jit_core.o\n \n ifeq ($(CONFIG_ARCH_RV64I),y)\n-\tobj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o\n+\tobj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o bpf_timed_may_goto.o\n else\n \tobj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o\n endif\ndiff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c\nindex c03c1de16b79ac..9832a19200c75c 100644\n--- a/arch/riscv/net/bpf_jit_comp64.c\n+++ b/arch/riscv/net/bpf_jit_comp64.c\n@@ -2157,3 +2157,8 @@ bool bpf_jit_supports_fsession(void)\n {\n \treturn true;\n }\n+\n+bool bpf_jit_supports_timed_may_goto(void)\n+{\n+\treturn true;\n+}\ndiff --git a/arch/riscv/net/bpf_timed_may_goto.S b/arch/riscv/net/bpf_timed_may_goto.S\nnew file mode 100644\nindex 00000000000000..f54f389d921e05\n--- /dev/null\n+++ b/arch/riscv/net/bpf_timed_may_goto.S\n@@ -0,0 +1,44 @@\n+/* SPDX-License-Identifier: GPL-2.0 */\n+/* Copyright (c) 2026 Feng Jiang \u003cjiangfeng@kylinos.cn\u003e */\n+\n+#include \u003clinux/linkage.h\u003e\n+#include \u003casm/asm.h\u003e\n+\n+/*\n+ * Trampoline for the BPF timed may_goto loop bound. Custom calling convention:\n+ *\t- input:  stack offset in BPF_REG_AX (t0)\n+ *\t- output: updated count in BPF_REG_AX (t0)\n+ *\n+ * Calls bpf_check_timed_may_goto(ptr) with the standard RISC-V ABI, where\n+ * ptr = BPF_REG_FP (s5) + BPF_REG_AX (t0). BPF R0-R5 (a5, a0-a4) are saved\n+ * across the call; BPF_REG_FP (s5) is callee-saved and needs no saving.\n+ */\n+\n+SYM_FUNC_START(arch_bpf_timed_may_goto)\n+\taddi\tsp, sp, -64\n+\tsd\tra, 56(sp)\n+\n+\t/* Save BPF registers R0-R5 (a5, a0-a4) */\n+\tsd\ta5, 48(sp)\n+\tsd\ta0, 40(sp)\n+\tsd\ta1, 32(sp)\n+\tsd\ta2, 24(sp)\n+\tsd\ta3, 16(sp)\n+\tsd\ta4, 8(sp)\n+\n+\tadd\ta0, t0, s5\n+\tcall\tbpf_check_timed_may_goto\n+\tmv\tt0, a0\n+\n+\t/* Restore BPF registers R0-R5 */\n+\tld\ta4, 8(sp)\n+\tld\ta3, 16(sp)\n+\tld\ta2, 24(sp)\n+\tld\ta1, 32(sp)\n+\tld\ta0, 40(sp)\n+\tld\ta5, 48(sp)\n+\n+\tld\tra, 56(sp)\n+\taddi\tsp, sp, 64\n+\tret\n+SYM_FUNC_END(arch_bpf_timed_may_goto)\ndiff --git a/tools/testing/selftests/bpf/progs/stream.c b/tools/testing/selftests/bpf/progs/stream.c\nindex 92ba1d72e0ece4..8d8e53d37266cd 100644\n--- a/tools/testing/selftests/bpf/progs/stream.c\n+++ b/tools/testing/selftests/bpf/progs/stream.c\n@@ -64,6 +64,7 @@ SEC(\"syscall\")\n __arch_x86_64\n __arch_arm64\n __arch_s390x\n+__arch_riscv64\n __success __retval(0)\n __stderr(\"ERROR: Timeout detected for may_goto instruction\")\n __stderr(\"CPU: {{[0-9]+}} UID: 0 PID: {{[0-9]+}} Comm: {{.*}}\")\ndiff --git a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c\nindex 4bdf4256a41e51..f47b9d540a1759 100644\n--- a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c\n+++ b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c\n@@ -11,6 +11,7 @@ __description(\"may_goto 0\")\n __arch_x86_64\n __arch_s390x\n __arch_arm64\n+__arch_riscv64\n __xlated(\"0: r0 = 1\")\n __xlated(\"1: exit\")\n __success\n@@ -31,6 +32,7 @@ __description(\"batch 2 of may_goto 0\")\n __arch_x86_64\n __arch_s390x\n __arch_arm64\n+__arch_riscv64\n __xlated(\"0: r0 = 1\")\n __xlated(\"1: exit\")\n __success\n@@ -53,6 +55,7 @@ __description(\"may_goto batch with offsets 2/1/0\")\n __arch_x86_64\n __arch_s390x\n __arch_arm64\n+__arch_riscv64\n __xlated(\"0: r0 = 1\")\n __xlated(\"1: exit\")\n __success\n@@ -79,6 +82,7 @@ __description(\"may_goto batch with offsets 2/0\")\n __arch_x86_64\n __arch_s390x\n __arch_arm64\n+__arch_riscv64\n __xlated(\"0: *(u64 *)(r10 -16) = 65535\")\n __xlated(\"1: *(u64 *)(r10 -8) = 0\")\n __xlated(\"2: r12 = *(u64 *)(r10 -16)\")\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "arch_bpf_timed_may_goto",
    "bpf_jit_supports_timed_may_goto"
  ],
  "Reasoning": "The patch implements architecture-specific support for the BPF timed may_goto loop bound on RISC-V 64-bit. It adds the arch_bpf_timed_may_goto assembly trampoline and enables it in the JIT compiler. This is functional code reachable by loading BPF programs with may_goto instructions on RISC-V.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. List them in the EnableConfigs output array,
   and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 44763c9bdfb67d695f6a41961d1b194aa3e93334
Author: syz-cluster <triage@syzkaller.com>
Date:   Tue Jul 14 08:02:21 2026 +0000

    syz-cluster: applied patch under review

diff --git a/arch/riscv/net/Makefile b/arch/riscv/net/Makefile
index 9a1e5f0a94e559..6458d4d51990a7 100644
--- a/arch/riscv/net/Makefile
+++ b/arch/riscv/net/Makefile
@@ -3,7 +3,7 @@
 obj-$(CONFIG_BPF_JIT) += bpf_jit_core.o
 
 ifeq ($(CONFIG_ARCH_RV64I),y)
-	obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
+	obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o bpf_timed_may_goto.o
 else
 	obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
 endif
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index c03c1de16b79ac..9832a19200c75c 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -2157,3 +2157,8 @@ bool bpf_jit_supports_fsession(void)
 {
 	return true;
 }
+
+bool bpf_jit_supports_timed_may_goto(void)
+{
+	return true;
+}
diff --git a/arch/riscv/net/bpf_timed_may_goto.S b/arch/riscv/net/bpf_timed_may_goto.S
new file mode 100644
index 00000000000000..f54f389d921e05
--- /dev/null
+++ b/arch/riscv/net/bpf_timed_may_goto.S
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2026 Feng Jiang <jiangfeng@kylinos.cn> */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+/*
+ * Trampoline for the BPF timed may_goto loop bound. Custom calling convention:
+ *	- input:  stack offset in BPF_REG_AX (t0)
+ *	- output: updated count in BPF_REG_AX (t0)
+ *
+ * Calls bpf_check_timed_may_goto(ptr) with the standard RISC-V ABI, where
+ * ptr = BPF_REG_FP (s5) + BPF_REG_AX (t0). BPF R0-R5 (a5, a0-a4) are saved
+ * across the call; BPF_REG_FP (s5) is callee-saved and needs no saving.
+ */
+
+SYM_FUNC_START(arch_bpf_timed_may_goto)
+	addi	sp, sp, -64
+	sd	ra, 56(sp)
+
+	/* Save BPF registers R0-R5 (a5, a0-a4) */
+	sd	a5, 48(sp)
+	sd	a0, 40(sp)
+	sd	a1, 32(sp)
+	sd	a2, 24(sp)
+	sd	a3, 16(sp)
+	sd	a4, 8(sp)
+
+	add	a0, t0, s5
+	call	bpf_check_timed_may_goto
+	mv	t0, a0
+
+	/* Restore BPF registers R0-R5 */
+	ld	a4, 8(sp)
+	ld	a3, 16(sp)
+	ld	a2, 24(sp)
+	ld	a1, 32(sp)
+	ld	a0, 40(sp)
+	ld	a5, 48(sp)
+
+	ld	ra, 56(sp)
+	addi	sp, sp, 64
+	ret
+SYM_FUNC_END(arch_bpf_timed_may_goto)
diff --git a/tools/testing/selftests/bpf/progs/stream.c b/tools/testing/selftests/bpf/progs/stream.c
index 92ba1d72e0ece4..8d8e53d37266cd 100644
--- a/tools/testing/selftests/bpf/progs/stream.c
+++ b/tools/testing/selftests/bpf/progs/stream.c
@@ -64,6 +64,7 @@ SEC("syscall")
 __arch_x86_64
 __arch_arm64
 __arch_s390x
+__arch_riscv64
 __success __retval(0)
 __stderr("ERROR: Timeout detected for may_goto instruction")
 __stderr("CPU: {{[0-9]+}} UID: 0 PID: {{[0-9]+}} Comm: {{.*}}")
diff --git a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
index 4bdf4256a41e51..f47b9d540a1759 100644
--- a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
+++ b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
@@ -11,6 +11,7 @@ __description("may_goto 0")
 __arch_x86_64
 __arch_s390x
 __arch_arm64
+__arch_riscv64
 __xlated("0: r0 = 1")
 __xlated("1: exit")
 __success
@@ -31,6 +32,7 @@ __description("batch 2 of may_goto 0")
 __arch_x86_64
 __arch_s390x
 __arch_arm64
+__arch_riscv64
 __xlated("0: r0 = 1")
 __xlated("1: exit")
 __success
@@ -53,6 +55,7 @@ __description("may_goto batch with offsets 2/1/0")
 __arch_x86_64
 __arch_s390x
 __arch_arm64
+__arch_riscv64
 __xlated("0: r0 = 1")
 __xlated("1: exit")
 __success
@@ -79,6 +82,7 @@ __description("may_goto batch with offsets 2/0")
 __arch_x86_64
 __arch_s390x
 __arch_arm64
+__arch_riscv64
 __xlated("0: *(u64 *)(r10 -16) = 65535")
 __xlated("1: *(u64 *)(r10 -8) = 0")
 __xlated("2: r12 = *(u64 *)(r10 -16)")

gemini-3.1-pro-preview

null

null

							input: 3504
							output: 24
							thoughts: 478
						

**RISC-V BPF JIT Support for `bpf_timed_may_goto` - Considerations for Fuzzing**

Okay, so I've got this patch adding support for `bpf_timed_may_goto` in the RISC-V BPF JIT. Essentially, it's adding architecture-specific support for an existing feature. Let's break it down: The patch modifies the `Makefile` to include the new object file, and it adds the necessary supporting function and assembly.

My initial thoughts are, "Is this going to be fuzzed effectively?".

I need to make sure this is actually being *exercised*. Syzkaller is the go-to tool for fuzzing and will catch many potential issues. Given that Syzkaller fuzzes RISC-V, this should, in principle, be reachable. The configs that are required (`CONFIG_BPF_JIT` and `CONFIG_ARCH_RV64I`) are pretty standard for enabling the JIT and targeting the 64-bit RISC-V architecture.

I'm thinking about the key components here: `bpf_jit_supports_timed_may_goto` is straightforward, but the real meat is `arch_bpf_timed_may_goto`, which is the assembly implementation. The critical question is, what C code actually *calls* `arch_bpf_timed_may_goto`? I need to understand the control flow. I'm going to quickly use `grepper` to see where that function is used within the kernel source. I need to understand the call graph to be sure that it is used and hence, fuzzed.

{
  "Expression": "arch_bpf_timed_may_goto"
}

{
  "Output": "arch/arm64/net/bpf_jit_comp.c=1253=static int build_insn(const struct bpf_verifier_env *env, const struct bpf_insn *insn,\n--\narch/arm64/net/bpf_jit_comp.c-1657-\t\t/*\narch/arm64/net/bpf_jit_comp.c:1658:\t\t * Call to arch_bpf_timed_may_goto() is emitted by the\narch/arm64/net/bpf_jit_comp.c-1659-\t\t * verifier and called with custom calling convention with\n--\narch/arm64/net/bpf_jit_comp.c-1661-\t\t */\narch/arm64/net/bpf_jit_comp.c:1662:\t\tif (func_addr != (u64)arch_bpf_timed_may_goto)\narch/arm64/net/bpf_jit_comp.c-1663-\t\t\temit(A64_MOV(1, r0, A64_R(0)), ctx);\n--\narch/arm64/net/bpf_timed_may_goto.S-5-\narch/arm64/net/bpf_timed_may_goto.S:6:SYM_FUNC_START(arch_bpf_timed_may_goto)\narch/arm64/net/bpf_timed_may_goto.S-7-\t/* Allocate stack space and emit frame record */\n--\narch/arm64/net/bpf_timed_may_goto.S-20-\t *\narch/arm64/net/bpf_timed_may_goto.S:21:\t * Before generating the call to arch_bpf_timed_may_goto, the verifier\narch/arm64/net/bpf_timed_may_goto.S-22-\t * generates a load instruction using FP, i.e. REG_AX = *(u64 *)(FP -\n--\narch/arm64/net/bpf_timed_may_goto.S-39-\tret\narch/arm64/net/bpf_timed_may_goto.S:40:SYM_FUNC_END(arch_bpf_timed_may_goto)\n--\narch/powerpc/net/bpf_jit_comp64.c=967=int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct codegen_context *ctx,\n--\narch/powerpc/net/bpf_jit_comp64.c-1769-\t\t\t/*\narch/powerpc/net/bpf_jit_comp64.c:1770:\t\t\t * Call to arch_bpf_timed_may_goto() is emitted by the\narch/powerpc/net/bpf_jit_comp64.c-1771-\t\t\t * verifier and called with custom calling convention with\n--\narch/powerpc/net/bpf_jit_comp64.c-1782-\narch/powerpc/net/bpf_jit_comp64.c:1783:\t\t\tif (func_addr == (u64)arch_bpf_timed_may_goto) {\narch/powerpc/net/bpf_jit_comp64.c-1784-\t\t\t\tret = 0;\n--\narch/powerpc/net/bpf_timed_may_goto.S-7-/*\narch/powerpc/net/bpf_timed_may_goto.S:8: * arch_bpf_timed_may_goto() trampoline for powerpc64\narch/powerpc/net/bpf_timed_may_goto.S-9- *\n--\narch/powerpc/net/bpf_timed_may_goto.S-19-\narch/powerpc/net/bpf_timed_may_goto.S:20:SYM_FUNC_START(arch_bpf_timed_may_goto)\narch/powerpc/net/bpf_timed_may_goto.S-21-\t/* Prologue: save LR, allocate frame */\n--\narch/powerpc/net/bpf_timed_may_goto.S-56-\tblr\narch/powerpc/net/bpf_timed_may_goto.S:57:SYM_FUNC_END(arch_bpf_timed_may_goto)\n--\narch/riscv/net/bpf_timed_may_goto.S-16-\narch/riscv/net/bpf_timed_may_goto.S:17:SYM_FUNC_START(arch_bpf_timed_may_goto)\narch/riscv/net/bpf_timed_may_goto.S-18-\taddi\tsp, sp, -64\n--\narch/riscv/net/bpf_timed_may_goto.S-43-\tret\narch/riscv/net/bpf_timed_may_goto.S:44:SYM_FUNC_END(arch_bpf_timed_may_goto)\n--\narch/s390/net/bpf_jit_comp.c=876=static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,\n--\narch/s390/net/bpf_jit_comp.c-1841-\narch/s390/net/bpf_jit_comp.c:1842:\t\tif ((void *)func == arch_bpf_timed_may_goto) {\narch/s390/net/bpf_jit_comp.c-1843-\t\t\t/*\narch/s390/net/bpf_jit_comp.c:1844:\t\t\t * arch_bpf_timed_may_goto() has a special ABI: the\narch/s390/net/bpf_jit_comp.c-1845-\t\t\t * parameters are in BPF_REG_AX and BPF_REG_10; the\n--\narch/s390/net/bpf_timed_may_goto.S-21-\narch/s390/net/bpf_timed_may_goto.S:22:SYM_FUNC_START(arch_bpf_timed_may_goto)\narch/s390/net/bpf_timed_may_goto.S-23-\t/*\n--\narch/s390/net/bpf_timed_may_goto.S-44-\tBR_EX %r1\narch/s390/net/bpf_timed_may_goto.S:45:SYM_FUNC_END(arch_bpf_timed_may_goto)\n--\narch/x86/net/bpf_timed_may_goto.S-10-\narch/x86/net/bpf_timed_may_goto.S:11:SYM_FUNC_START(arch_bpf_timed_may_goto)\narch/x86/net/bpf_timed_may_goto.S-12-\tANNOTATE_NOENDBR\n--\narch/x86/net/bpf_timed_may_goto.S-54-\tRET\narch/x86/net/bpf_timed_may_goto.S:55:SYM_FUNC_END(arch_bpf_timed_may_goto)\n--\ninclude/linux/filter.h=1194=void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie);\ninclude/linux/filter.h:1195:u64 arch_bpf_timed_may_goto(void);\ninclude/linux/filter.h-1196-u64 bpf_check_timed_may_goto(struct bpf_timed_may_goto *);\n--\nkernel/bpf/core.c=3325=bool __weak bpf_jit_supports_timed_may_goto(void)\n--\nkernel/bpf/core.c-3329-\nkernel/bpf/core.c:3330:u64 __weak arch_bpf_timed_may_goto(void)\nkernel/bpf/core.c-3331-{\n--\nkernel/bpf/fixups.c=1481=int bpf_do_misc_fixups(struct bpf_verifier_env *env)\n--\nkernel/bpf/fixups.c-1765-\t\t\t * until the value becomes 0 in AX (thus, 1 in stack),\nkernel/bpf/fixups.c:1766:\t\t\t * after which we call arch_bpf_timed_may_goto, which\nkernel/bpf/fixups.c-1767-\t\t\t * either sets AX to 0xffff to keep looping, or to 0\n--\nkernel/bpf/fixups.c-1783-\t\t\t * (to add to r10/fp), and also as the return value of\nkernel/bpf/fixups.c:1784:\t\t\t * the call to arch_bpf_timed_may_goto.\nkernel/bpf/fixups.c-1785-\t\t\t */\nkernel/bpf/fixups.c-1786-\t\t\tinsn_buf[4] = BPF_MOV64_IMM(BPF_REG_AX, stack_off_cnt);\nkernel/bpf/fixups.c:1787:\t\t\tinsn_buf[5] = BPF_EMIT_CALL(arch_bpf_timed_may_goto);\nkernel/bpf/fixups.c-1788-\t\t\tinsn_buf[6] = BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_AX, stack_off_cnt);\n"
}

gemini-3.1-pro-preview

null

null

							input: 6776
							output: 37
							thoughts: 126
						

**Investigating RISC-V BPF JIT Handling of `may_goto`**

Okay, so the BPF JIT calls `arch_bpf_timed_may_goto` when it encounters those `may_goto` instructions. That makes sense. Hmm, wait a second... looking at `arch/riscv/net/bpf_jit_comp64.c`, I'm not seeing any explicit handling of `arch_bpf_timed_may_goto` in that file, particularly around where that function *should* be utilized, according to the architecture. That's unusual. I better double-check around the use of `arch_bpf_timed_may_goto` within `bpf_jit_comp64.c` to see if there's something I'm missing. This warrants a closer look.

{
  "Expression": "arch_bpf_timed_may_goto",
  "PathPrefix": "arch/riscv/net/"
}

{
  "Output": "arch/riscv/net/bpf_timed_may_goto.S-16-\narch/riscv/net/bpf_timed_may_goto.S:17:SYM_FUNC_START(arch_bpf_timed_may_goto)\narch/riscv/net/bpf_timed_may_goto.S-18-\taddi\tsp, sp, -64\n--\narch/riscv/net/bpf_timed_may_goto.S-43-\tret\narch/riscv/net/bpf_timed_may_goto.S:44:SYM_FUNC_END(arch_bpf_timed_may_goto)\n"
}

gemini-3.1-pro-preview

null

null

							input: 7291
							output: 41
							thoughts: 407
						

**RISC-V BPF JIT and `arch_bpf_timed_may_goto`**

Okay, so I was thinking about how the RISC-V JIT handles `arch_bpf_timed_may_goto`. Initially, I assumed it wouldn't require any special treatment, that it'd simply emit a standard call to it. But then I remembered that `arch_bpf_timed_may_goto` is a BPF helper call. The verifier emits `BPF_EMIT_CALL(arch_bpf_timed_may_goto)`, right?

So, the JIT *should* just compile that as a normal call. But hang on, `arch_bpf_timed_may_goto` has a *custom* calling convention! I need to be sure the JIT accounts for this.

Let's look at `arch/riscv/net/bpf_timed_may_goto.S`. Ah, yes. It's a trampoline. The input is a stack offset in `BPF_REG_AX` (t0), and the output is the updated count, also in `BPF_REG_AX` (t0). It calls `bpf_check_timed_may_goto(ptr)`, where `ptr` is the result of `BPF_REG_FP` (s5) + `BPF_REG_AX` (t0). BPF registers R0-R5 (a5, a0-a4) are saved across the call; BPF_REG_FP (s5) is callee-saved, so no saving is needed.

So, the verifier emits a call to `arch_bpf_timed_may_goto`, and the JIT translates this to a call to `arch_bpf_timed_may_goto`. This all seems correct. But how exactly does the JIT translate a call to a fixed address in RISC-V? I need to refresh my memory on the specifics of this. Let's check `arch/riscv/net/bpf_jit_comp64.c` to see how `BPF_CALL` is handled there. That's where I'll find the details I need.

{
  "Expression": "BPF_CALL",
  "PathPrefix": "arch/riscv/net/bpf_jit_comp64.c"
}

{
  "Output": "arch/riscv/net/bpf_jit_comp64.c=406=static void init_regs(u8 *rd, u8 *rs, const struct bpf_insn *insn,\n--\narch/riscv/net/bpf_jit_comp64.c-412-\tcase BPF_JMP | BPF_JA:\narch/riscv/net/bpf_jit_comp64.c:413:\tcase BPF_JMP | BPF_CALL:\narch/riscv/net/bpf_jit_comp64.c-414-\tcase BPF_JMP | BPF_EXIT:\n--\narch/riscv/net/bpf_jit_comp64.c=1369=int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,\n--\narch/riscv/net/bpf_jit_comp64.c-1789-\t/* function call */\narch/riscv/net/bpf_jit_comp64.c:1790:\tcase BPF_JMP | BPF_CALL:\narch/riscv/net/bpf_jit_comp64.c-1791-\t{\n"
}

gemini-3.1-pro-preview

null

null

							input: 8544
							output: 46
							thoughts: 39
						

Okay, let's dive into this.

**Examining the RISC-V BPF JIT Compilation for Calls**

Alright, I need to understand how the `BPF_JMP | BPF_CALL` instruction is handled within the RISC-V BPF JIT compiler. I need to get into the details of the implementation. Let me pull up the source code, specifically `arch/riscv/net/bpf_jit_comp64.c`. I expect to find the meat of the translation process there. I want to see how this specific BPF opcode is mapped to RISC-V instructions. I need to understand the register allocation strategies, the handling of function arguments, and the mechanics of the call itself. What RISC-V instructions are being used? How is the return address managed? Are there any optimizations being done specifically for this type of jump? This is going to give me insight into the performance characteristics of BPF on this architecture and let me see potential areas for improvement. Let's see how they've approached this critical part of the BPF execution engine.

{
  "File": "arch/riscv/net/bpf_jit_comp64.c",
  "FirstLine": 1789,
  "LineCount": 50
}

{
  "Contents": "1789:\t\t/* function call */\n1790:\t\tcase BPF_JMP | BPF_CALL:\n1791:\t\t{\n1792:\t\t\tbool fixed_addr;\n1793:\t\t\tu64 addr;\n1794:\t\n1795:\t\t\t/* Inline calls to bpf_get_smp_processor_id()\n1796:\t\t\t *\n1797:\t\t\t * RV_REG_TP holds the address of the current CPU's task_struct and thread_info is\n1798:\t\t\t * at offset 0 in task_struct.\n1799:\t\t\t * Load cpu from thread_info:\n1800:\t\t\t *     Set R0 to ((struct thread_info *)(RV_REG_TP))-\u003ecpu\n1801:\t\t\t *\n1802:\t\t\t * This replicates the implementation of raw_smp_processor_id() on RISCV\n1803:\t\t\t */\n1804:\t\t\tif (insn-\u003esrc_reg == 0 \u0026\u0026 insn-\u003eimm == BPF_FUNC_get_smp_processor_id) {\n1805:\t\t\t\t/* Load current CPU number in R0 */\n1806:\t\t\t\temit_lw(bpf_to_rv_reg(BPF_REG_0, ctx), offsetof(struct thread_info, cpu),\n1807:\t\t\t\t\tRV_REG_TP, ctx);\n1808:\t\t\t\tbreak;\n1809:\t\t\t}\n1810:\t\n1811:\t\t\t/* Implement helper call to bpf_get_current_task/_btf() inline */\n1812:\t\t\tif (insn-\u003esrc_reg == 0 \u0026\u0026 (insn-\u003eimm == BPF_FUNC_get_current_task ||\n1813:\t\t\t\t\t\t   insn-\u003eimm == BPF_FUNC_get_current_task_btf)) {\n1814:\t\t\t\temit_mv(bpf_to_rv_reg(BPF_REG_0, ctx), RV_REG_TP, ctx);\n1815:\t\t\t\tbreak;\n1816:\t\t\t}\n1817:\t\n1818:\t\t\tmark_call(ctx);\n1819:\t\t\tret = bpf_jit_get_func_addr(ctx-\u003eprog, insn, extra_pass,\n1820:\t\t\t\t\t\t    \u0026addr, \u0026fixed_addr);\n1821:\t\t\tif (ret \u003c 0)\n1822:\t\t\t\treturn ret;\n1823:\t\n1824:\t\t\tif (insn-\u003esrc_reg == BPF_PSEUDO_KFUNC_CALL) {\n1825:\t\t\t\tconst struct btf_func_model *fm;\n1826:\t\t\t\tint idx;\n1827:\t\n1828:\t\t\t\tfm = bpf_jit_find_kfunc_model(ctx-\u003eprog, insn);\n1829:\t\t\t\tif (!fm)\n1830:\t\t\t\t\treturn -EINVAL;\n1831:\t\n1832:\t\t\t\tfor (idx = 0; idx \u003c fm-\u003enr_args; idx++) {\n1833:\t\t\t\t\tu8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx);\n1834:\t\n1835:\t\t\t\t\tif (fm-\u003earg_size[idx] == sizeof(int))\n1836:\t\t\t\t\t\temit_sextw(reg, reg, ctx);\n1837:\t\t\t\t}\n1838:\t\t\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 9718
							output: 46
							thoughts: 45
						

Here's my take on the thought process:

**Decoding the BPF Call Instruction**

Okay, so `bpf_jit_get_func_addr` is going to hand me that address, that's the key. That's how this is going to work. The system is set up to issue a call. Now, let's just make sure I'm following the flow correctly. I need to dive into the specifics of `BPF_JMP | BPF_CALL`. Let's see how that's all hooked up... I want to make sure I understand how it all comes together. This instruction is critical to understand.

{
  "File": "arch/riscv/net/bpf_jit_comp64.c",
  "FirstLine": 1839,
  "LineCount": 50
}

{
  "Contents": "1839:\t\n1840:\t\t\tret = emit_call(addr, fixed_addr, ctx);\n1841:\t\t\tif (ret)\n1842:\t\t\t\treturn ret;\n1843:\t\n1844:\t\t\tif (insn-\u003esrc_reg != BPF_PSEUDO_CALL)\n1845:\t\t\t\temit_mv(bpf_to_rv_reg(BPF_REG_0, ctx), RV_REG_A0, ctx);\n1846:\t\t\tbreak;\n1847:\t\t}\n1848:\t\t/* tail call */\n1849:\t\tcase BPF_JMP | BPF_TAIL_CALL:\n1850:\t\t\tif (emit_bpf_tail_call(i, ctx))\n1851:\t\t\t\treturn -1;\n1852:\t\t\tbreak;\n1853:\t\n1854:\t\t/* function return */\n1855:\t\tcase BPF_JMP | BPF_EXIT:\n1856:\t\t\tif (i == ctx-\u003eprog-\u003elen - 1)\n1857:\t\t\t\tbreak;\n1858:\t\n1859:\t\t\trvoff = epilogue_offset(ctx);\n1860:\t\t\tret = emit_jump_and_link(RV_REG_ZERO, rvoff, true, ctx);\n1861:\t\t\tif (ret)\n1862:\t\t\t\treturn ret;\n1863:\t\t\tbreak;\n1864:\t\n1865:\t\t/* dst = imm64 */\n1866:\t\tcase BPF_LD | BPF_IMM | BPF_DW:\n1867:\t\t{\n1868:\t\t\tstruct bpf_insn insn1 = insn[1];\n1869:\t\t\tu64 imm64;\n1870:\t\n1871:\t\t\timm64 = (u64)insn1.imm \u003c\u003c 32 | (u32)imm;\n1872:\t\t\tif (bpf_pseudo_func(insn)) {\n1873:\t\t\t\t/* fixed-length insns for extra jit pass */\n1874:\t\t\t\tret = emit_addr(rd, imm64, extra_pass, ctx);\n1875:\t\t\t\tif (ret)\n1876:\t\t\t\t\treturn ret;\n1877:\t\t\t} else {\n1878:\t\t\t\temit_imm(rd, imm64, ctx);\n1879:\t\t\t}\n1880:\t\n1881:\t\t\treturn 1;\n1882:\t\t}\n1883:\t\n1884:\t\t/* LDX: dst = *(unsigned size *)(src + off) */\n1885:\t\tcase BPF_LDX | BPF_MEM | BPF_B:\n1886:\t\tcase BPF_LDX | BPF_MEM | BPF_H:\n1887:\t\tcase BPF_LDX | BPF_MEM | BPF_W:\n1888:\t\tcase BPF_LDX | BPF_MEM | BPF_DW:\n"
}

gemini-3.1-pro-preview

null

null

							input: 10721
							output: 40
							thoughts: 121
						

**Analyzing the BPF JIT Call Emission**

Okay, so I see this code is simply emitting a call to `addr`. Simple enough, but a red flag just went up. Hang on, the `arch_bpf_timed_may_goto` function actually *expects* the stack offset in `BPF_REG_AX`, which translates to `t0` in the RISC-V BPF JIT, and it *also* returns the updated count in that very same register, `t0`. That's important for the control flow.

But wait a minute… won't `emit_call` potentially clobber `t0`? That's a major problem if it does. I need to verify that; I need to make *absolutely* sure `emit_call` preserves `t0`. Better go directly to the source. Let's pull up `arch/riscv/net/bpf_jit_comp64.c` and check the implementation of `emit_call` there. I have to confirm the register usage so as to avoid a nasty, unexpected bug, that would take forever to debug.

{
  "Expression": "emit_call",
  "PathPrefix": "arch/riscv/net/bpf_jit_comp64.c"
}

{
  "Output": "arch/riscv/net/bpf_jit_comp64.c=447=static bool is_signed_bpf_cond(u8 cond)\n--\narch/riscv/net/bpf_jit_comp64.c-452-\narch/riscv/net/bpf_jit_comp64.c:453:static int emit_call(u64 addr, bool fixed_addr, struct rv_jit_context *ctx)\narch/riscv/net/bpf_jit_comp64.c-454-{\n--\narch/riscv/net/bpf_jit_comp64.c=937=static int invoke_bpf_prog(struct bpf_tramp_node *node, int args_off, int retval_off,\n--\narch/riscv/net/bpf_jit_comp64.c-952-\temit_addi(RV_REG_A1, RV_REG_FP, -run_ctx_off, ctx);\narch/riscv/net/bpf_jit_comp64.c:953:\tret = emit_call((const u64)bpf_trampoline_enter(p), true, ctx);\narch/riscv/net/bpf_jit_comp64.c-954-\tif (ret)\n--\narch/riscv/net/bpf_jit_comp64.c-971-\t\temit_imm(RV_REG_A1, (const s64)p-\u003einsnsi, ctx);\narch/riscv/net/bpf_jit_comp64.c:972:\tret = emit_call((const u64)p-\u003ebpf_func, true, ctx);\narch/riscv/net/bpf_jit_comp64.c-973-\tif (ret)\n--\narch/riscv/net/bpf_jit_comp64.c-993-\temit_addi(RV_REG_A2, RV_REG_FP, -run_ctx_off, ctx);\narch/riscv/net/bpf_jit_comp64.c:994:\tret = emit_call((const u64)bpf_trampoline_exit(p), true, ctx);\narch/riscv/net/bpf_jit_comp64.c-995-\n--\narch/riscv/net/bpf_jit_comp64.c=1022=static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,\n--\narch/riscv/net/bpf_jit_comp64.c-1184-\t\temit_imm(RV_REG_A0, ctx-\u003einsns ? (const s64)im : RV_MAX_COUNT_IMM, ctx);\narch/riscv/net/bpf_jit_comp64.c:1185:\t\tret = emit_call((const u64)__bpf_tramp_enter, true, ctx);\narch/riscv/net/bpf_jit_comp64.c-1186-\t\tif (ret)\n--\narch/riscv/net/bpf_jit_comp64.c-1220-\t\trestore_stack_args(nr_arg_slots - RV_MAX_REG_ARGS, args_off, stk_arg_off, ctx);\narch/riscv/net/bpf_jit_comp64.c:1221:\t\tret = emit_call((const u64)orig_call, true, ctx);\narch/riscv/net/bpf_jit_comp64.c-1222-\t\tif (ret)\n--\narch/riscv/net/bpf_jit_comp64.c-1253-\t\temit_imm(RV_REG_A0, ctx-\u003einsns ? (const s64)im : RV_MAX_COUNT_IMM, ctx);\narch/riscv/net/bpf_jit_comp64.c:1254:\t\tret = emit_call((const u64)__bpf_tramp_exit, true, ctx);\narch/riscv/net/bpf_jit_comp64.c-1255-\t\tif (ret)\n--\narch/riscv/net/bpf_jit_comp64.c=1369=int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,\n--\narch/riscv/net/bpf_jit_comp64.c-1839-\narch/riscv/net/bpf_jit_comp64.c:1840:\t\tret = emit_call(addr, fixed_addr, ctx);\narch/riscv/net/bpf_jit_comp64.c-1841-\t\tif (ret)\n"
}

gemini-3.1-pro-preview

null

null

							input: 12314
							output: 45
							thoughts: 9
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Analyzing the Function Call**

Alright, let's dive into this `emit_call` function. My initial thought is to immediately parse the name and what the inputs are. Depending on the context I might be expecting a certain kind of behavior, but I really have to look and see.

I need to understand its role within the larger system. Is it a core component, or a helper function? What kind of data is it operating on, and what is the intended output? This name strongly suggests it's involved in dispatching or triggering something, so I'm already anticipating an investigation of how the call's parameters are handled and what they relate to. I'm going to want to check for error handling, of course. Proper error handling, or lack thereof, can be a major source of system vulnerabilities, so I'm primed to look for that immediately. I'll need to follow the execution path closely, looking for potential areas of concern like race conditions, unintended side effects, or inefficient code. Then again, it could be a straightforward function. I'll need to judge that once I've had a look.

{
  "File": "arch/riscv/net/bpf_jit_comp64.c",
  "FirstLine": 453,
  "LineCount": 20
}

{
  "Contents": " 453:\tstatic int emit_call(u64 addr, bool fixed_addr, struct rv_jit_context *ctx)\n 454:\t{\n 455:\t\ts64 off = 0;\n 456:\t\tu64 ip;\n 457:\t\n 458:\t\tif (addr \u0026\u0026 ctx-\u003einsns \u0026\u0026 ctx-\u003ero_insns) {\n 459:\t\t\t/*\n 460:\t\t\t * Use the ro_insns(RX) to calculate the offset as the BPF\n 461:\t\t\t * program will finally run from this memory region.\n 462:\t\t\t */\n 463:\t\t\tip = (u64)(long)(ctx-\u003ero_insns + ctx-\u003eninsns);\n 464:\t\t\toff = addr - ip;\n 465:\t\t}\n 466:\t\n 467:\t\treturn emit_jump_and_link(RV_REG_RA, off, fixed_addr, ctx);\n 468:\t}\n 469:\t\n 470:\tstatic inline void emit_kcfi(u32 hash, struct rv_jit_context *ctx)\n 471:\t{\n 472:\t\tif (IS_ENABLED(CONFIG_CFI))\n"
}

gemini-3.1-pro-preview

null

null

							input: 12956
							output: 39
							thoughts: 65
						

Here's my summary, as the expert:

**Understanding the `emit_jump_and_link` Function**

Okay, so I'm looking at `emit_jump_and_link`. It's using `RV_REG_RA`, which is standard for the return address register, good. And it's not messing with `t0` which is `RV_REG_T0`, so it's not stepping on anything that it shouldn't. Makes sense. But wait a minute... I need to be absolutely certain on this - what's `BPF_REG_AX` actually *mapped* to in the RISC-V register architecture? Gotta double-check that mapping. Just confirming that's not going to cause some weird conflict or unexpected behavior down the line. That's a crucial thing to get right.

no matches

{
  "Expression": "BPF_REG_AX",
  "PathPrefix": "arch/riscv/net/bpf_jit.h"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 13253
							output: 33
							thoughts: 52
						

Here's my thought process on the matter:

**Delving into RISC-V BPF JIT Implementation**

Okay, so I'm trying to figure out how register allocation works for BPF JIT on RISC-V. My immediate thought is to zero in on a function or macro responsible for translating BPF instructions to RISC-V register assignments. The name `bpf_to_rv_reg` is a likely candidate, or something with a similar naming convention, and it's probably defined within the RISC-V specific networking code. That means I should look in either `arch/riscv/net/bpf_jit.h`, which would contain the declarations, or `arch/riscv/net/bpf_jit_comp64.c`, which would probably hold the implementation details. Let's start with those locations, and see what the code has to offer. I need to understand how the BPF virtual registers map to physical RISC-V registers during JIT compilation. This is the key to performance, really.

{
  "Expression": "BPF_REG_AX",
  "PathPrefix": "arch/riscv/net/"
}

{
  "Output": "arch/riscv/net/bpf_jit_comp32.c=43=enum {\n--\narch/riscv/net/bpf_jit_comp32.c-54-\tBPF_AX_LO,\narch/riscv/net/bpf_jit_comp32.c:55:\t/* Stack space for BPF_REG_6 through BPF_REG_9 and BPF_REG_AX. */\narch/riscv/net/bpf_jit_comp32.c-56-\tBPF_JIT_SCRATCH_REGS,\n--\narch/riscv/net/bpf_jit_comp32.c=71=static const s8 bpf2rv32[][2] = {\n--\narch/riscv/net/bpf_jit_comp32.c-90-\t/* Temporary register for blinding constants. Stored on the stack. */\narch/riscv/net/bpf_jit_comp32.c:91:\t[BPF_REG_AX] = {STACK_OFFSET(BPF_AX_HI), STACK_OFFSET(BPF_AX_LO)},\narch/riscv/net/bpf_jit_comp32.c-92-\t/*\n--\narch/riscv/net/bpf_jit_comp64.c=29=static const int regmap[] = {\n--\narch/riscv/net/bpf_jit_comp64.c-40-\t[BPF_REG_FP] =\tRV_REG_S5,\narch/riscv/net/bpf_jit_comp64.c:41:\t[BPF_REG_AX] =\tRV_REG_T0,\narch/riscv/net/bpf_jit_comp64.c-42-};\n--\narch/riscv/net/bpf_timed_may_goto.S-8- * Trampoline for the BPF timed may_goto loop bound. Custom calling convention:\narch/riscv/net/bpf_timed_may_goto.S:9: *\t- input:  stack offset in BPF_REG_AX (t0)\narch/riscv/net/bpf_timed_may_goto.S:10: *\t- output: updated count in BPF_REG_AX (t0)\narch/riscv/net/bpf_timed_may_goto.S-11- *\narch/riscv/net/bpf_timed_may_goto.S-12- * Calls bpf_check_timed_may_goto(ptr) with the standard RISC-V ABI, where\narch/riscv/net/bpf_timed_may_goto.S:13: * ptr = BPF_REG_FP (s5) + BPF_REG_AX (t0). BPF R0-R5 (a5, a0-a4) are saved\narch/riscv/net/bpf_timed_may_goto.S-14- * across the call; BPF_REG_FP (s5) is callee-saved and needs no saving.\n"
}

gemini-3.1-pro-preview

null

null

							input: 14312
							output: 34
							thoughts: 750
						

**RISC-V BPF `may_goto` Implementation Analysis**

Alright, let me break down what's happening here. It looks like we're setting up the `may_goto` loop bound check for RISC-V. The `BPF_REG_AX` register is mapped to `RV_REG_T0`, so the verifier is emitting this sequence of instructions:

1.  `BPF_MOV64_IMM(BPF_REG_AX, stack_off_cnt)`: This moves an immediate value representing an offset count onto `t0`.
2.  `BPF_EMIT_CALL(arch_bpf_timed_may_goto)`: This is the key. The JIT will translate this into a call to the `arch_bpf_timed_may_goto` function.
3.  `BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_AX, stack_off_cnt)`: This instruction stores a double-word value from `t0` to a memory location.

Now, the `arch_bpf_timed_may_goto` assembly is what's really interesting:

```assembly
SYM_FUNC_START(arch_bpf_timed_may_goto)
	addi	sp, sp, -64
	sd	ra, 56(sp)

	/* Save BPF registers R0-R5 (a5, a0-a4) */
	sd	a5, 48(sp)
	sd	a0, 40(sp)
	sd	a1, 32(sp)
	sd	a2, 24(sp)
	sd	a3, 16(sp)
	sd	a4, 8(sp)

	add	a0, t0, s5
	call	bpf_check_timed_may_goto
	mv	t0, a0

	/* Restore BPF registers R0-R5 */
	ld	a4, 8(sp)
	ld	a3, 16(sp)
	ld	a2, 24(sp)
	ld	a1, 32(sp)
	ld	a0, 40(sp)
	ld	a5, 48(sp)

	ld	ra, 56(sp)
	addi	sp, sp, 64
	ret
SYM_FUNC_END(arch_bpf_timed_may_goto)
```

This assembly saves the BPF registers `R0-R5` (which are equivalent to `a5, a0-a4` in the RISC-V calling convention). Then, it calculates a value, `a0 = t0 + s5`, which effectively means adding `BPF_REG_AX + BPF_REG_FP`, passes this to the `bpf_check_timed_may_goto` function, and puts the result back into `t0`, and finally restores the BPF registers and returns.

This is a pretty clean implementation to enable the `may_goto` loop bound check on RISC-V, which is what we need to safely execute potentially unbounded loops in BPF programs.

So, is this change actually reachable? Absolutely, assuming we load a BPF program utilizing `may_goto` on a RISC-V system.

As far as configurations go, we'll need `CONFIG_BPF_JIT` for the JIT compiler, and the standard RISC-V configuration `CONFIG_ARCH_RV64I`. We actually don't need to specify `CONFIG_ARCH_RV64I` since it is the default 64-bit architecture config, but it doesn't hurt to explicitly define it. And, obviously, `CONFIG_BPF_SYSCALL` is essential to be able to load any BPF programs in the first place.

Let's do a quick check in the `arch/riscv/net/Makefile` to see if there are any other specific configurations required for BPF support, just to be sure.

{
  "File": "arch/riscv/net/Makefile",
  "FirstLine": 1,
  "LineCount": 10
}

{
  "Contents": "   1:\t# SPDX-License-Identifier: GPL-2.0-only\n   2:\t\n   3:\tobj-$(CONFIG_BPF_JIT) += bpf_jit_core.o\n   4:\t\n   5:\tifeq ($(CONFIG_ARCH_RV64I),y)\n   6:\t\tobj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o bpf_timed_may_goto.o\n   7:\telse\n   8:\t\tobj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o\n   9:\tendif\n"
}

gemini-3.1-pro-preview

null

null

							input: 16177
							output: 147
							thoughts: 845
						

**Analysis of the BPF Timed May_Goto Patch for RISC-V**

Okay, so I'm looking at this patch that adds RISC-V support for the `bpf_timed_may_goto` loop bound. The only configurations impacted here seem to be `CONFIG_BPF_JIT` and `CONFIG_ARCH_RV64I`, which is expected for a RISC-V addition.

Now, let's think about `FocusSymbols`. The core of this patch seems to revolve around the new `arch_bpf_timed_may_goto` function, which is, importantly, assembly. Syzkaller doesn't directly fuzz assembly well through coverage, though it can fuzz the BPF programs that trigger the functionality. There's also `bpf_jit_supports_timed_may_goto`, which the patch also adds.

The verifier emits a call, and the JIT compiles it. The C function `bpf_check_timed_may_goto` is called from the assembly, but this isn't modified in the patch. I was initially thinking about adding `bpf_check_timed_may_goto` to `FocusSymbols`, but it's not actually changed in this patch.

The patch modifies `bpf_jit_supports_timed_may_goto` and adds `arch_bpf_timed_may_goto`. Since `arch_bpf_timed_may_goto` is in assembly, it might not have coverage. `bpf_jit_supports_timed_may_goto` is just `return true;`. Hmm. So, it's not a complicated function.

No other functions are added in the patch. I'll double-check for other file modifications. Okay, I see `tools/testing/selftests/bpf/progs/stream.c` and `tools/testing/selftests/bpf/progs/verifier_may_goto_1.c` are also modified. So, the patch is functional, adding RISC-V support for `bpf_timed_may_goto`.

Given that, `WorthFuzzing` is definitely `true`.

For `EnableConfigs`, `BPF_JIT` is definitely required. `ARCH_RV64I` is standard for riscv64, so it's a given. Also, `BPF_SYSCALL` is necessary to use BPF. I'm going to list just `BPF_JIT`.

For `FocusSymbols`, I have to be smart here. The prompt says to focus on functions with complex logic, but avoid generic hotpaths. The relevant functions here are `arch_bpf_timed_may_goto` (even though it's assembly, it's worth a shot, might have some instrumentation) and `bpf_jit_supports_timed_may_goto`. I will include `bpf_jit_supports_timed_may_goto` and `arch_bpf_timed_may_goto`.

Let me quickly re-iterate: usually `.S` files are not instrumented by KCOV unless explicitly enabled, and even then, it's tricky. But it doesn't hurt to include it.

Based on the patch, the reasoning is "The patch implements architecture-specific support for the BPF timed may_goto loop bound on RISC-V 64-bit. It adds the arch_bpf_timed_may_goto assembly trampoline and enables it in the JIT compiler. This is functional code reachable by loading BPF programs with may_goto instructions on RISC-V."

Time to call `set-results`.

the following configs do not exist in the kernel tree: ARCH_RV64I

{
  "EnableConfigs": [
    "BPF_JIT",
    "ARCH_RV64I"
  ],
  "FocusSymbols": [
    "arch_bpf_timed_may_goto",
    "bpf_jit_supports_timed_may_goto"
  ],
  "Reasoning": "The patch implements architecture-specific support for the BPF timed may_goto loop bound on RISC-V 64-bit. It adds the arch_bpf_timed_may_goto assembly trampoline and enables it in the JIT compiler. This is functional code reachable by loading BPF programs with may_goto instructions on RISC-V.",
  "WorthFuzzing": true
}

{
  "error": "the following configs do not exist in the kernel tree: ARCH_RV64I"
}

gemini-3.1-pro-preview

null

null

							input: 17984
							output: 32
							thoughts: 26
						

Okay, here's my summary, tailored as requested:

**Investigating the Missing Architecture Identifier**

Hmm, so `ARCH_RV64I` isn't defined, is that right? That's... unexpected. Okay, let me quickly double-check the architecture configuration in `arch/riscv/Kconfig`. That's the first logical place to look for the definition or potentially any relevant includes. I need to understand why this symbol is undefined before I go down a rabbit hole. Let's see if it's conditionally defined or if I just need to add it there. Let's get to the bottom of this.

{
  "Expression": "config ARCH_RV64I",
  "PathPrefix": "arch/riscv/"
}

{
  "Output": "arch/riscv/Kconfig=405=config ARCH_RV32I\n--\narch/riscv/Kconfig-410-\narch/riscv/Kconfig:411:config ARCH_RV64I\narch/riscv/Kconfig-412-\tbool \"RV64I\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 18265
							output: 138
							thoughts: 79
						

**Debugging a Kernel Configuration Mystery**

Okay, hold on a second. I could have sworn I saw this thing – whatever "this thing" is, let's call it the configuration option - in the RISC-V architecture files. Specifically, I remember seeing it in `arch/riscv/Kconfig`. So, what did `set-results` report? That it doesn't exist? That's… strange. Something's clearly not right here.

Aha! Perhaps the issue isn't whether the option *exists*, but how the tool is looking for it. Maybe the configuration name isn't precisely what the tool is expecting. Is it possible the tool is checking the *global* Kconfig file, and it’s actually architecture-specific, defined under something like `ARCH_RV64I`? Or, equally likely, this could be a simple bug in the tool itself. I’ve seen weirder things in these kinds of environments.

Alright, let's not waste any more time wrestling with this rabbit hole. I'll just fall back to the tried and true approach of using `BPF_JIT`. That should work. I'll take a look at the RISC-V architecture later to see if I can figure out what went wrong.

{
  "EnableConfigs": [
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "arch_bpf_timed_may_goto",
    "bpf_jit_supports_timed_may_goto"
  ],
  "Reasoning": "The patch implements architecture-specific support for the BPF timed may_goto loop bound on RISC-V 64-bit. It adds the arch_bpf_timed_may_goto assembly trampoline and enables it in the JIT compiler. This is functional code reachable by loading BPF programs with may_goto instructions on RISC-V.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "arch_bpf_timed_may_goto",
    "bpf_jit_supports_timed_may_goto"
  ],
  "Reasoning": "The patch implements architecture-specific support for the BPF timed may_goto loop bound on RISC-V 64-bit. It adds the arch_bpf_timed_may_goto assembly trampoline and enables it in the JIT compiler. This is functional code reachable by loading BPF programs with may_goto instructions on RISC-V.",
  "WorthFuzzing": true
}