DW_OP_fbreg means the parameter value will be stored on the stack. So the corresponding parameter register is not used. For example: 0x071f7717: DW_TAG_subprogram DW_AT_name ("jent_health_failure") DW_AT_calling_convention (DW_CC_nocall) DW_AT_type (0x071f7626 "unsigned int") ... 0x071f7728: DW_TAG_formal_parameter DW_AT_location (DW_OP_fbreg -8) DW_AT_name ("ec") DW_AT_type (0x071f7ab6 "rand_data *") ... 0x071f7734: NULL In the above, the parameter 'ec' type is a pointer so it perfectly fits into a register. But the location uses 'DW_OP_fbreg -8' which prevents from generating a function with true signatures. Signed-off-by: Yonghong Song --- dwarf_loader.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index 7da3926..d538607 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -1196,6 +1196,7 @@ struct func_info { }; #define PARM_DEFAULT_FAIL -1 +#define PARM_FAIL_CLANG -2 /* For DW_AT_location 'attr': * - if first location is DW_OP_regXX with expected number, return the register; @@ -1204,7 +1205,7 @@ struct func_info { * list, return the register; otherwise save register for later return * - otherwise if no register was found for locations, return PARM_DEFAULT_FAIL. */ -static int parameter__reg(Dwarf_Attribute *attr, int expected_reg) +static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct cu *cu, struct conf_load *conf) { Dwarf_Addr base, start, end; Dwarf_Op *expr, *entry_ops; @@ -1240,6 +1241,16 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg) if (ret == expected_reg) goto out; break; + case DW_OP_fbreg: + /* The locaiton like + * DW_AT_location (DW_OP_fbreg +) + * indicates that the parameter is on the stack. But it is possible + * that the parameter can fit in register(s). So conservatively + * mark this parameter not suitable for true signatures. + */ + if (cu->producer_clang && conf->true_signature) + ret = PARM_FAIL_CLANG; + break; /* match DW_OP_entry_value(DW_OP_regXX) at any location */ case DW_OP_entry_value: case DW_OP_GNU_entry_value: @@ -1328,11 +1339,11 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, if (parm->has_loc) { int expected_reg = cu->register_params[reg_idx]; - int actual_reg = parameter__reg(&attr, expected_reg); + int actual_reg = parameter__reg(&attr, expected_reg, cu, conf); if (actual_reg == PARM_DEFAULT_FAIL) parm->optimized = 1; - else if (expected_reg >= 0 && expected_reg != actual_reg) + else if (actual_reg == PARM_FAIL_CLANG || (expected_reg >= 0 && expected_reg != actual_reg)) /* mark parameters that use an unexpected * register to hold a parameter; these will * be problematic for users of BTF as they -- 2.47.3