Commit 3f5928e4 authored by Namhyung Kim's avatar Namhyung Kim Committed by Arnaldo Carvalho de Melo
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perf dwarf-aux: Add die_find_variable_by_reg() helper 



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: default avatarNamhyung Kim <namhyung@kernel.org>
Acked-by: default avatarMasami 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 981620fd

tools/perf/util/dwarf-aux.c

+67 −0
Original line number Diff line number Diff line
@@ -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



/*

tools/perf/util/dwarf-aux.h

+12 −0
Original line number Diff line number Diff line
@@ -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 */