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perf dwarf-aux: Add die_find_variable_by_reg() helper

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The die_find_variable_by_reg() will search for a variable or a parameter
sub-DIE in the given scope DIE where the location matches to the given
register.

For the simplest and most common case, memory access usually happens
with a base register and an offset to the field so the register holds a
pointer in a variable or function parameter.  Then we can find one if it
has a location expression at the (instruction) address.  This function
only handles such a simple case for now.

In this case, the expression has a DW_OP_regN operation where N < 32.
If the register index (N) is greater than or equal to 32, DW_OP_regx
operation with an operand which saves the value for the N would be used.
It rejects expressions with more operations.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: linux-toolchains@vger.kernel.org
Cc: linux-trace-devel@vger.kernel.org
Link: https://lore.kernel.org/r/20231110000012.3538610-8-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Namhyung Kim 2023-11-09 15:59:26 -08:00 committed by Arnaldo Carvalho de Melo
parent 981620fd27
commit 3f5928e461
2 changed files with 79 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

67
tools/perf/util/dwarf-aux.c
View File

@ -1245,6 +1245,73 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
out:
return ret;
}
/* Interval parameters for __die_find_var_reg_cb() */
struct find_var_data {
/* Target instruction address */
Dwarf_Addr pc;
/* Target register */
unsigned reg;
};
/* Max number of registers DW_OP_regN supports */
#define DWARF_OP_DIRECT_REGS 32
/* Only checks direct child DIEs in the given scope. */
static int __die_find_var_reg_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_Op *ops;
size_t nops;
if (tag != DW_TAG_variable && tag != DW_TAG_formal_parameter)
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) {
/* Assuming the location list is sorted by address */
if (end < data->pc)
continue;
if (start > data->pc)
break;
/* Only match with a simple case */
if (data->reg < DWARF_OP_DIRECT_REGS) {
if (ops->atom == (DW_OP_reg0 + data->reg) && nops == 1)
return DIE_FIND_CB_END;
} else {
if (ops->atom == DW_OP_regx && ops->number == data->reg &&
nops == 1)
return DIE_FIND_CB_END;
}
}
return DIE_FIND_CB_SIBLING;
}
/**
* die_find_variable_by_reg - Find a variable saved in a register
* @sc_die: a scope DIE
* @pc: the program address to find
* @reg: the register number to find
* @die_mem: a buffer to save the resulting DIE
*
* Find the variable DIE accessed by the given register.
*/
Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
Dwarf_Die *die_mem)
{
struct find_var_data data = {
.pc = pc,
.reg = reg,
};
return die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
}
#endif
/*

12
tools/perf/util/dwarf-aux.h
View File

@ -137,6 +137,10 @@ int die_get_scopes(Dwarf_Die *cu_die, Dwarf_Addr pc, Dwarf_Die **scopes);
/* Get byte offset range of given variable DIE */
int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
/* Find a variable saved in the 'reg' at given address */
Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
Dwarf_Die *die_mem);
#else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
@ -146,6 +150,14 @@ static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
return -ENOTSUP;
}
static inline Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die __maybe_unused,
Dwarf_Addr pc __maybe_unused,
int reg __maybe_unused,
Dwarf_Die *die_mem __maybe_unused)
{
return NULL;
}
#endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
#endif /* _DWARF_AUX_H */