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perf dwarf-aux: Add die_same_file() and die_get_type_die()

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dwarf_dieoffset() is relative to the file the DIE is in, so an offset
saved by die_collect_vars()/die_collect_global_vars() is only
meaningful in that file: add die_same_file(), comparing the Dwarf each
DIE's CU belongs to, and die_get_type_die(), resolving the offset in it
with the saved tag as a sanity check.  Resolving the offset in the main
file instead parses whatever is at it when it came from the dwz common
file.

dwarf_cu_getdwarf() is new in elfutils 0.160, so the libdw feature test
probes for it and Makefile.config says 0.160.

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Assisted-by: LLM
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo 2026-09-24 16:27:56 -03:00
parent a6ac1e9ca9
commit 3dfdd195c7
4 changed files with 77 additions and 4 deletions
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10
tools/build/feature/test-libdw.c
View File

@ -49,8 +49,16 @@ int test_elfutils(void)
return 0;
}
/* Needs elfutils 0.160: taking its address fails the probe, not the link. */
int test_libdw_cu_getdwarf(void)
{
void *sym = (void *)dwarf_cu_getdwarf;
return sym == NULL;
}
int main(void)
{
return test_libdw() + test_libdw_unwind() + test_libdw_getlocations() +
test_libdw_getcfi() + test_elfutils();
test_libdw_getcfi() + test_libdw_cu_getdwarf() + test_elfutils();
}

2
tools/perf/Makefile.config
View File

@ -477,7 +477,7 @@ else
else
ifneq ($(feature-libdw), 1)
ifndef NO_LIBDW
$(warning No libdw.h found or old libdw.h found or elfutils is older than 0.157, disables dwarf support. Please install new elfutils-devel/libdw-dev)
$(warning No libdw.h found or old libdw.h found or elfutils is older than 0.160, disables dwarf support. Please install new elfutils-devel/libdw-dev)
NO_LIBDW := 1
endif
endif # Dwarf support

56
tools/perf/util/dwarf-aux.c
View File

@ -1677,6 +1677,15 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr addr,
return result;
}
/*
* Whether two DIEs live in the same debug file: dwarf_dieoffset() is
* relative to the file the DIE is in.
*/
bool die_same_file(Dwarf_Die *die_a, Dwarf_Die *die_b)
{
return dwarf_cu_getdwarf(die_a->cu) == dwarf_cu_getdwarf(die_b->cu);
}
static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
{
struct die_var_type **var_types = arg;
@ -1721,6 +1730,8 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
vt->is_reg_var_addr = true;
vt->die_off = dwarf_dieoffset(&type_die);
vt->die_tag = dwarf_tag(&type_die);
vt->from_alt = !die_same_file(die_mem, &type_die);
vt->addr = start;
vt->end = end;
vt->has_range = (end != 0 || start != 0);
@ -1740,7 +1751,8 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
*
* Save all variables and parameters in the @sc_die and save them to @var_types.
* The @var_types is a singly-linked list containing type and location info.
* Actual type can be retrieved using dwarf_offdie() with 'die_off' later.
* Actual type can be retrieved using die_get_type_die() with 'die_off',
* 'die_tag' and 'from_alt' later.
*
* Callers should free @var_types.
*/
@ -1786,6 +1798,8 @@ static int __die_collect_global_vars_cb(Dwarf_Die *die_mem, void *arg)
return DIE_FIND_CB_END;
vt->die_off = dwarf_dieoffset(&type_die);
vt->die_tag = dwarf_tag(&type_die);
vt->from_alt = !die_same_file(die_mem, &type_die);
vt->addr = ops->number;
vt->end = 0;
vt->has_range = false;
@ -1797,6 +1811,43 @@ static int __die_collect_global_vars_cb(Dwarf_Die *die_mem, void *arg)
return DIE_FIND_CB_SIBLING;
}
/**
* die_get_type_die - Get a type DIE saved by die_collect_vars()
* @dbg: the main debug info
* @die_off: offset of the type DIE, from dwarf_dieoffset()
* @die_tag: tag that DIE had when the offset was saved
* @from_alt: whether the type DIE is in the dwz alt file
* @die_mem: where to store the resulting DIE
*
* Resolve @die_off in the file it was recorded as belonging to, with no
* fallback; @die_tag is a sanity check.
*/
Dwarf_Die *die_get_type_die(Dwarf *dbg, u64 die_off, int die_tag, bool from_alt,
Dwarf_Die *die_mem)
{
Dwarf *target = dbg;
Dwarf_Die die;
if (from_alt) {
/* No fallback: an alt offset here parses whatever is at it. */
target = dwarf_getalt(dbg);
if (target == NULL) {
pr_debug("DWARF: no alt (dwz) debug file to resolve the type DIE at offset 0x%lx in\n",
(unsigned long)die_off);
return NULL;
}
}
if (dwarf_offdie(target, die_off, &die) && dwarf_tag(&die) == die_tag) {
*die_mem = die;
return die_mem;
}
pr_debug("DWARF: no DIE with tag %d at offset 0x%lx in the %s debug file\n",
die_tag, (unsigned long)die_off, from_alt ? "alt" : "main");
return NULL;
}
/**
* die_collect_global_vars - Save all global variables
* @cu_die: a CU DIE
@ -1804,7 +1855,8 @@ static int __die_collect_global_vars_cb(Dwarf_Die *die_mem, void *arg)
*
* Save all global variables in the @cu_die and save them to @var_types.
* The @var_types is a singly-linked list containing type and location info.
* Actual type can be retrieved using dwarf_offdie() with 'die_off' later.
* Actual type can be retrieved using die_get_type_die() with 'die_off',
* 'die_tag' and 'from_alt' later.
*
* Callers should free @var_types.
*/

13
tools/perf/util/dwarf-aux.h
View File

@ -152,6 +152,8 @@ int die_get_scopes(Dwarf_Die *cu_die, Dwarf_Addr pc, Dwarf_Die **scopes);
struct die_var_type {
struct die_var_type *next;
u64 die_off;
int die_tag;
bool from_alt; /* die_off is relative to the alt (dwz) file */
u64 addr;
u64 end; /* end address of location range */
int reg;
@ -183,6 +185,17 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr addr,
/* Save all variables and parameters in this scope */
void die_collect_vars(Dwarf_Die *sc_die, struct die_var_type **var_types);
/*
* Get the type DIE saved by die_collect_vars()/die_collect_global_vars():
* @from_alt says which file the offset must be resolved in, @die_tag is
* a sanity check.
*/
Dwarf_Die *die_get_type_die(Dwarf *dbg, u64 die_off, int die_tag, bool from_alt,
Dwarf_Die *die_mem);
/* Whether two DIEs live in the same debug file */
bool die_same_file(Dwarf_Die *die_a, Dwarf_Die *die_b);
/* Save all global variables in this CU */
void die_collect_global_vars(Dwarf_Die *cu_die, struct die_var_type **var_types);