For llvm dwarf, the dead argument may be in the middle of DW_TAG_subprogram. So we introduce skip_idx in order to match expected registers properly. For example: 0x00042897: DW_TAG_subprogram DW_AT_name ("create_dev") DW_AT_calling_convention (DW_CC_nocall) DW_AT_type (0x0002429a "int") ... 0x000428ab: DW_TAG_formal_parameter DW_AT_name ("name") DW_AT_type (0x000242ed "char *") ... 0x000428b5: DW_TAG_formal_parameter DW_AT_location (indexed (0x3f) loclist = 0x000027f8: [0xffffffff87681370, 0xffffffff8768137a): DW_OP_reg5 RDI [0xffffffff8768137a, 0xffffffff87681392): DW_OP_reg3 RBX [0xffffffff87681392, 0xffffffff876813ae): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value) DW_AT_name ("dev") DW_AT_type (0x00026859 "dev_t") ... With skip_idx, we can identify that the second original argument 'dev' becomes the first one after optimization. The previous patch has the following: 0x0533fd03: DW_TAG_subprogram DW_AT_name ("acpi_irq_penalty_update") DW_AT_calling_convention (DW_CC_nocall) DW_AT_type (0x05334dc7 "int") ... 0x0533fd15: DW_TAG_formal_parameter DW_AT_name ("str") DW_AT_type (0x05335918 "char *") ... 0x0533fd1f: DW_TAG_formal_parameter DW_AT_location (indexed (0x3b) loclist = 0x00eb9d83: [0xffff80008419f2e0, 0xffff80008419f324): DW_OP_reg1 W1 [0xffff80008419f324, 0xffff80008419f47c): DW_OP_reg19 W19 [0xffff80008419f47c, 0xffff80008419f494): DW_OP_entry_value(DW_OP_reg1 W1), DW_OP_stack_value [0xffff80008419f494, 0xffff80008419f498): DW_OP_reg19 W19) DW_AT_name ("used") DW_AT_type (0x05334dc7 "int") ... It is also handled properly with parameter 'str' will have W0 register. With this patch, I checked x86_64 that the number of invalid true signatures is reduced from 532 to 96. This suggests that majority of optimized functions are caused by dead arguments. Signed-off-by: Yonghong Song --- dwarf_loader.c | 93 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 88 insertions(+), 5 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index 412a73e..c1b7763 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -1195,10 +1195,62 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr, struct func_info { bool signature_changed; + int skip_idx; int nr_params; int param_start_regs[MAX_PRESCAN_PARAMS]; }; +static int __get_type_byte_size(Dwarf_Die *die, struct cu *cu) +{ + Dwarf_Attribute attr; + if (dwarf_attr(die, DW_AT_type, &attr) == NULL) + return 0; + + Dwarf_Die type_die; + if (dwarf_formref_die(&attr, &type_die) == NULL) + return 0; + + /* A type does not have byte_size. + * 0x000dac83: DW_TAG_formal_parameter + DW_AT_location (indexed (0x385) loclist = 0x00016175: + [0xffff800080098cb0, 0xffff800080098cb4): DW_OP_breg8 W8+0 + [0xffff800080098cb4, 0xffff800080098ff4): DW_OP_breg31 WSP+16, DW_OP_deref + [0xffff800080099054, 0xffff80008009908c): DW_OP_breg31 WSP+16, DW_OP_deref) + DW_AT_name ("ubuf") + DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/arm64/kernel/ptrace.c") + DW_AT_decl_line (886) + DW_AT_type (0x000d467e "const void *") + + * 0x000d467e: DW_TAG_pointer_type + DW_AT_type (0x000c4320 "const void") + + * 0x000c4320: DW_TAG_const_type + */ + if (dwarf_tag(&type_die) == DW_TAG_pointer_type) + return cu->addr_size; + + uint64_t bsize = attr_numeric(&type_die, DW_AT_byte_size); + if (bsize == 0) + return __get_type_byte_size(&type_die, cu); + + return bsize; +} + +static int get_type_byte_size(Dwarf_Die *die, struct cu *cu) +{ + int byte_size = 0; + + Dwarf_Attribute attr; + if (dwarf_attr(die, DW_AT_abstract_origin, &attr)) { + Dwarf_Die origin; + if (dwarf_formref_die(&attr, &origin)) + byte_size = __get_type_byte_size(&origin, cu); + } else { + byte_size = __get_type_byte_size(die, cu); + } + return byte_size; +} + /* Get the first DW_OP_X (should be a register) from a parameter's DW_AT_location. */ static int parameter__peek_first_reg(Dwarf_Die *die) { @@ -1292,8 +1344,9 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, struct parameter *parm = tag__alloc(cu, sizeof(*parm)); if (parm != NULL) { - bool has_const_value; + bool has_const_value, true_sig_enabled; Dwarf_Attribute attr; + int reg_idx; tag__init(&parm->tag, cu, die); parm->name = attr_string(die, DW_AT_name, conf); @@ -1303,8 +1356,10 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, if (!info->signature_changed) { if (cu->producer_clang || param_idx >= cu->nr_register_params) return parm; - } else if (param_idx >= cu->nr_register_params) { - return parm; + } else { + reg_idx = param_idx - info->skip_idx; + if (reg_idx >= cu->nr_register_params) + return parm; } /* Parameters which use DW_AT_abstract_origin to point at @@ -1342,9 +1397,10 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, */ has_const_value = dwarf_attr(die, DW_AT_const_value, &attr) != NULL; parm->has_loc = dwarf_attr(die, DW_AT_location, &attr) != NULL; + true_sig_enabled = conf->true_signature && info->signature_changed; if (parm->has_loc) { - int expected_reg = cu->register_params[param_idx]; + int expected_reg = cu->register_params[reg_idx]; int actual_reg = parameter__reg(&attr, expected_reg); if (actual_reg < 0) @@ -1357,8 +1413,35 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, * contents. */ parm->unexpected_reg = 1; - } else if (has_const_value) { + } else if (has_const_value && !cu->producer_clang) { + parm->optimized = 1; + } else if (true_sig_enabled) { + int byte_size, num_regs, next_reg_idx; + + if (param_idx + 1 < info->nr_params) { + int next_start = info->param_start_regs[param_idx + 1]; + if (next_start >= 0) { + /* check whether we should preserve the argument or not */ + byte_size = get_type_byte_size(die, cu); + /* byte_size 0 should not happen. */ + if (!byte_size) { + parm->unexpected_reg = 1; + return parm; + } + + num_regs = (byte_size + cu->addr_size - 1) / cu->addr_size; + next_reg_idx = reg_idx + num_regs; + if (next_reg_idx < cu->nr_register_params && + next_start == cu->register_params[next_reg_idx]) { + if (byte_size > cu->addr_size) + info->skip_idx--; + return parm; + } + } + } + parm->optimized = 1; + info->skip_idx++; } } -- 2.52.0