On Wed, 11 Oct 2023 20:50:51 -0700
Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> The die_find_variable_by_addr() is to find a variables in the given DIE
> using given (PC-relative) address. Global variables will have a
> location expression with DW_OP_addr which has an address so can simply
> compare it with the address.
>
> <1><143a7>: Abbrev Number: 2 (DW_TAG_variable)
> <143a8> DW_AT_name : loops_per_jiffy
> <143ac> DW_AT_type : <0x1cca>
> <143b0> DW_AT_external : 1
> <143b0> DW_AT_decl_file : 193
> <143b1> DW_AT_decl_line : 213
> <143b2> DW_AT_location : 9 byte block: 3 b0 46 41 82 ff ff ff ff
> (DW_OP_addr: ffffffff824146b0)
>
> Note that the type-offset should be calculated from the base address of
> the global variable.
>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
BTW, for the global variable, you can also find it via maps. Can't you?
Thanks,
> ---
> tools/perf/util/dwarf-aux.c | 80 +++++++++++++++++++++++++++++++++++++
> tools/perf/util/dwarf-aux.h | 14 +++++++
> 2 files changed, 94 insertions(+)
>
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 5bb05c84d249..97d9ae56350e 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1266,8 +1266,12 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
> struct find_var_data {
> /* Target instruction address */
> Dwarf_Addr pc;
> + /* Target memory address (for global data) */
> + Dwarf_Addr addr;
> /* Target register */
> unsigned reg;
> + /* Access offset, set for global data */
> + int offset;
> };
>
> /* Max number of registers DW_OP_regN supports */
> @@ -1328,6 +1332,82 @@ Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
> };
> return die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
> }
> +
> +/* Only checks direct child DIEs in the given scope */
> +static int __die_find_var_addr_cb(Dwarf_Die *die_mem, void *arg)
> +{
> + struct find_var_data *data = arg;
> + int tag = dwarf_tag(die_mem);
> + ptrdiff_t off = 0;
> + Dwarf_Attribute attr;
> + Dwarf_Addr base, start, end;
> + Dwarf_Word size;
> + Dwarf_Die type_die;
> + Dwarf_Op *ops;
> + size_t nops;
> +
> + if (tag != DW_TAG_variable)
> + return DIE_FIND_CB_SIBLING;
> +
> + if (dwarf_attr(die_mem, DW_AT_location, &attr) == NULL)
> + return DIE_FIND_CB_SIBLING;
> +
> + while ((off = dwarf_getlocations(&attr, off, &base, &start, &end, &ops, &nops)) > 0) {
> + if (ops->atom != DW_OP_addr)
> + continue;
> +
> + if (data->addr < ops->number)
> + continue;
> +
> + if (data->addr == ops->number) {
> + /* Update offset relative to the start of the variable */
> + data->offset = 0;
> + return DIE_FIND_CB_END;
> + }
> +
> + if (die_get_real_type(die_mem, &type_die) == NULL)
> + continue;
> +
> + if (dwarf_aggregate_size(&type_die, &size) < 0)
> + continue;
> +
> + if (data->addr >= ops->number + size)
> + continue;
> +
> + /* Update offset relative to the start of the variable */
> + data->offset = data->addr - ops->number;
> + return DIE_FIND_CB_END;
> + }
> + return DIE_FIND_CB_SIBLING;
> +}
> +
> +/**
> + * die_find_variable_by_addr - Find variable located at given address
> + * @sc_die: a scope DIE
> + * @pc: the program address to find
> + * @addr: the data address to find
> + * @die_mem: a buffer to save the resulting DIE
> + * @offset: the offset in the resulting type
> + *
> + * Find the variable DIE located at the given address (in PC-relative mode).
> + * This is usually for global variables.
> + */
> +Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
> + Dwarf_Addr addr, Dwarf_Die *die_mem,
> + int *offset)
> +{
> + struct find_var_data data = {
> + .pc = pc,
> + .addr = addr,
> + };
> + Dwarf_Die *result;
> +
> + result = die_find_child(sc_die, __die_find_var_addr_cb, &data, die_mem);
> + if (result)
> + *offset = data.offset;
> + return result;
> +}
> +
> #endif
>
> /*
> diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
> index 574405c57d3b..742098e3ee7e 100644
> --- a/tools/perf/util/dwarf-aux.h
> +++ b/tools/perf/util/dwarf-aux.h
> @@ -144,6 +144,11 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
> Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
> Dwarf_Die *die_mem);
>
> +/* Find a (global) variable located in the 'addr' */
> +Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
> + Dwarf_Addr addr, Dwarf_Die *die_mem,
> + int *offset);
> +
> #else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
>
> static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
> @@ -161,6 +166,15 @@ static inline Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die __maybe_unus
> return NULL;
> }
>
> +static inline Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die __maybe_unused,
> + Dwarf_Addr pc __maybe_unused,
> + Dwarf_Addr addr __maybe_unused,
> + Dwarf_Die *die_mem __maybe_unused,
> + int *offset __maybe_unused)
> +{
> + return NULL;
> +}
> +
> #endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
>
> #endif /* _DWARF_AUX_H */
> --
> 2.42.0.655.g421f12c284-goog
>
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
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