On Wed, 11 Oct 2023 20:50:54 -0700
Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> The die_get_cfa() is to get frame base register and offset at the given
> instruction address (pc). This info will be used to locate stack
> variables which have location expression using DW_OP_fbreg.
>
In the util/probe-finder.c, I added the elfutils version checker
#if _ELFUTILS_PREREQ(0, 142)
for CFI related code, in commit 7752f1b096e1 ("perf probe: Don't
compile CFI related code if elfutils is old"). Maybe we'd better to have
a config of HAVE_DWARF_CFI_SUPPORT for this.
Thank you,
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
> tools/perf/util/dwarf-aux.c | 64 +++++++++++++++++++++++++++++++++++++
> tools/perf/util/dwarf-aux.h | 9 ++++++
> 2 files changed, 73 insertions(+)
>
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 97d9ae56350e..796413eb4e8f 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1408,6 +1408,70 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
> return result;
> }
>
> +static int reg_from_dwarf_op(Dwarf_Op *op)
> +{
> + switch (op->atom) {
> + case DW_OP_reg0 ... DW_OP_reg31:
> + return op->atom - DW_OP_reg0;
> + case DW_OP_breg0 ... DW_OP_breg31:
> + return op->atom - DW_OP_breg0;
> + case DW_OP_regx:
> + case DW_OP_bregx:
> + return op->number;
> + default:
> + break;
> + }
> + return -1;
> +}
> +
> +static int offset_from_dwarf_op(Dwarf_Op *op)
> +{
> + switch (op->atom) {
> + case DW_OP_reg0 ... DW_OP_reg31:
> + case DW_OP_regx:
> + return 0;
> + case DW_OP_breg0 ... DW_OP_breg31:
> + return op->number;
> + case DW_OP_bregx:
> + return op->number2;
> + default:
> + break;
> + }
> + return -1;
> +}
> +
> +/**
> + * die_get_cfa - Get frame base information
> + * @dwarf: a Dwarf info
> + * @pc: program address
> + * @preg: pointer for saved register
> + * @poffset: pointer for saved offset
> + *
> + * This function gets register and offset for CFA (Canonical Frame Address)
> + * by searching the CIE/FDE info. The CFA usually points to the start address
> + * of the current stack frame and local variables can be located using an offset
> + * from the CFA. The @preg and @poffset will be updated if it returns 0.
> + */
> +int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset)
> +{
> + Dwarf_CFI *cfi;
> + Dwarf_Frame *frame = NULL;
> + Dwarf_Op *ops = NULL;
> + size_t nops;
> +
> + cfi = dwarf_getcfi(dwarf);
> + if (cfi == NULL)
> + return -1;
> +
> + if (!dwarf_cfi_addrframe(cfi, pc, &frame) &&
> + !dwarf_frame_cfa(frame, &ops, &nops) && nops == 1) {
> + *preg = reg_from_dwarf_op(ops);
> + *poffset = offset_from_dwarf_op(ops);
> + return 0;
> + }
> + return -1;
> +}
> +
> #endif
>
> /*
> diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
> index 742098e3ee7e..29a7243b1a45 100644
> --- a/tools/perf/util/dwarf-aux.h
> +++ b/tools/perf/util/dwarf-aux.h
> @@ -149,6 +149,9 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
> Dwarf_Addr addr, Dwarf_Die *die_mem,
> int *offset);
>
> +/* Get the frame base information from CFA */
> +int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset);
> +
> #else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
>
> static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
> @@ -175,6 +178,12 @@ static inline Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die __maybe_unu
> return NULL;
> }
>
> +static inline int die_get_cfa(Dwarf *dwarf __maybe_unused, u64 pc __maybe_unused,
> + int *preg __maybe_unused, int *poffset __maybe_unused)
> +{
> + return -1;
> +}
> +
> #endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
>
> #endif /* _DWARF_AUX_H */
> --
> 2.42.0.655.g421f12c284-goog
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
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