* [PATCH 1/3] perf libdw: Optimize fallback logic for missing DWARF
2026-10-26 6:50 [PATCH 0/3] perf: Fix libdw addr2line fallback, pr_debugN overhead, and cumulative hist decay Ian Rogers
@ 2026-10-26 6:50 ` Ian Rogers
2026-10-26 6:50 ` [PATCH 2/3] perf debug: Avoid calling eprintf() in pr_debugN() when verbose < n Ian Rogers
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Ian Rogers @ 2026-10-26 6:50 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo, Namhyung Kim, Alireza Haghdoost, Ian Rogers
Cc: Peter Zijlstra, Ingo Molnar, Jiri Olsa, Adrian Hunter,
James Clark, Alessio Podda, Michael Liang, Shimin Guo,
Tanushree Shah, linux-perf-users, linux-kernel
When libdw encounters a DWARF definition it cannot accurately un-inline
or an address block natively missing structural line maps,
dwfl_module_getsrc() returns NULL. Previously, libdw__addr2line()
returned -1 in both dwfl_module_getdwarf() and dwfl_module_getsrc()
failure paths while addr2line() in srcline.c only stopped its fallback
loop on ret > 0. This caused perf's addr2line_style loop to fall back to
llvm, libbfd, and the cmd__addr2line() subprocess wrapper on every
unmapped address or stripped DSO.
Update the addr2line_style pipeline return semantics consistently:
1. Backends return 0 to denote conclusively missing information
(e.g. valid ELF but no DWARF inside, or parsed DWARF with no mapped
lines), stopping the fallback loop.
2. Backends (and uncompiled stubs) return < 0 to denote initialization
or backend errors, instructing the loop to iterate to the next
configured fallback.
3. Backends return > 0 on successful source line resolution.
Fixes: bf96e296d52d ("perf libdw: Fix Dwfl discovery with split files")
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/addr2line.c | 28 ++++++++++---
tools/perf/util/dso.h | 2 +-
tools/perf/util/libbfd.c | 6 +--
tools/perf/util/libdw.c | 25 ++++++++---
tools/perf/util/libdw.h | 5 ++-
tools/perf/util/llvm-c-helpers.cpp | 66 +++++++++++++++++++-----------
tools/perf/util/llvm.c | 12 ++++--
tools/perf/util/srcline.c | 21 +++++++---
8 files changed, 115 insertions(+), 50 deletions(-)
diff --git a/tools/perf/util/addr2line.c b/tools/perf/util/addr2line.c
index 6f64f6b42442..960dd48701bb 100644
--- a/tools/perf/util/addr2line.c
+++ b/tools/perf/util/addr2line.c
@@ -298,6 +298,7 @@ int cmd__addr2line(const char *dso_name, u64 addr,
struct io io = { .eof = false };
enum cmd_a2l_style cmd_a2l_style;
const char *current_dso_name;
+ bool a2l_synced = false;
mutex_lock(dso__lock(dso));
current_dso_name = dso__symsrc_filename(dso) ?: dso_name;
@@ -316,11 +317,14 @@ int cmd__addr2line(const char *dso_name, u64 addr,
if (a2l == NULL) {
if (!symbol_conf.addr2line_disable_warn)
pr_warning("%s %s: addr2line_subprocess_init failed\n", __func__, dso_name);
+ ret = -1;
goto out_unlock;
}
cmd_a2l_style = cmd_addr2line_configure(a2l, dso_name);
- if (cmd_a2l_style == BROKEN)
+ if (cmd_a2l_style == BROKEN) {
+ ret = -1;
goto out_unlock;
+ }
/*
* Take ownership of the a2l subprocess so we can safely perform
@@ -344,6 +348,7 @@ int cmd__addr2line(const char *dso_name, u64 addr,
if (written != len) {
if (!symbol_conf.addr2line_disable_warn)
pr_warning("%s %s: could not send request\n", __func__, dso_name);
+ ret = -1;
goto out;
}
io__init(&io, a2l->out, buf, sizeof(buf));
@@ -353,6 +358,7 @@ int cmd__addr2line(const char *dso_name, u64 addr,
case -1:
if (!symbol_conf.addr2line_disable_warn)
pr_warning("%s %s: could not read first record\n", __func__, dso_name);
+ ret = -1;
goto out;
case 0:
/*
@@ -373,6 +379,7 @@ int cmd__addr2line(const char *dso_name, u64 addr,
break;
case 0:
/* The sentinel as expected. */
+ a2l_synced = true;
break;
default:
if (!symbol_conf.addr2line_disable_warn)
@@ -388,17 +395,23 @@ int cmd__addr2line(const char *dso_name, u64 addr,
if (file) {
*file = strdup(record_filename);
- ret = 1;
+ if (!*file) {
+ ret = -ENOMEM;
+ goto out;
+ }
}
if (line_nr)
*line_nr = record_line_nr;
+ ret = 1;
if (unwind_inlines) {
if (node && inline_list__append_record(dso, node, sym,
record_function,
record_filename,
record_line_nr)) {
- ret = 0;
+ if (file && *file)
+ zfree(file);
+ ret = -ENOMEM;
goto out;
}
}
@@ -421,12 +434,17 @@ int cmd__addr2line(const char *dso_name, u64 addr,
record_function,
record_filename,
record_line_nr)) {
- ret = 0;
+ if (file && *file)
+ zfree(file);
+ inline_node__clear_frames(node);
+ ret = -ENOMEM;
goto out;
}
ret = 1; /* found at least one inline frame */
}
}
+ if (record_status == 0)
+ a2l_synced = true;
out:
mutex_lock(dso__lock(dso));
@@ -434,7 +452,7 @@ int cmd__addr2line(const char *dso_name, u64 addr,
free(record_filename);
current_dso_name = dso__symsrc_filename(dso) ?: dso__long_name(dso);
- if (!io.eof && dso__a2l(dso) == NULL && current_dso_name &&
+ if (a2l_synced && !io.eof && dso__a2l(dso) == NULL && current_dso_name &&
!strcmp(current_dso_name, dso_name))
dso__set_a2l(dso, a2l);
else
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 3329f417810c..d5f7382d4e13 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -760,7 +760,7 @@ static inline const char *dso__symsrc_filename(const struct dso *dso)
return RC_CHK_ACCESS(dso)->symsrc_filename;
}
-void dso__set_symsrc_filename(struct dso *dso, char *val);
+void dso__set_symsrc_filename(struct dso *dso, char *val) EXCLUSIVE_LOCKS_REQUIRED(dso__lock(dso));
static inline void dso__free_symsrc_filename(struct dso *dso)
{
diff --git a/tools/perf/util/libbfd.c b/tools/perf/util/libbfd.c
index a4dcb406c79e..992e2c2a7198 100644
--- a/tools/perf/util/libbfd.c
+++ b/tools/perf/util/libbfd.c
@@ -288,7 +288,7 @@ int libbfd__addr2line(const char *dso_name, u64 addr,
if (node && inline_list__append_dso_a2l(dso, node, sym)) {
inline_node__clear_frames(node);
- ret = 0;
+ ret = -ENOMEM;
goto out;
}
@@ -302,7 +302,7 @@ int libbfd__addr2line(const char *dso_name, u64 addr,
if (node != NULL) {
if (inline_list__append_dso_a2l(dso, node, sym)) {
inline_node__clear_frames(node);
- ret = 0;
+ ret = -ENOMEM;
goto out;
}
}
@@ -312,7 +312,7 @@ int libbfd__addr2line(const char *dso_name, u64 addr,
if (file) {
*file = a2l->filename ? strdup(a2l->filename) : NULL;
if (!*file) {
- /* Leave ret as 0 so that another addr2line is tried. */
+ ret = a2l->filename ? -ENOMEM : 0;
goto out;
}
}
diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
index c4504cceb313..e660623338d5 100644
--- a/tools/perf/util/libdw.c
+++ b/tools/perf/util/libdw.c
@@ -7,6 +7,7 @@
#include "callchain.h"
#include <fcntl.h>
#include <unistd.h>
+#include <string.h>
#include <elfutils/libdwfl.h>
static const Dwfl_Callbacks offline_callbacks = {
@@ -175,10 +176,15 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
int lineno = 0;
int ret = 0;
+ if (!dso__has_srcline(dso))
+ return 0;
+
mutex_lock(dso__lock(dso));
dwfl = dso__libdw_dwfl(dso);
- if (!dwfl)
+ if (!dwfl) {
+ ret = -1;
goto out;
+ }
mod = dwfl_addrmodule(dwfl, addr);
if (!mod) {
@@ -192,14 +198,23 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
* libdw.
*/
if (!dwfl_module_getdwarf(mod, &bias)) {
- ret = -1;
+ /*
+ * Free the Dwfl session so the mmap'd ELF binary is unmapped
+ * immediately, and mark the DSO as lacking srcline/DWARF info
+ * so neither libdw nor slower fallback backends (addr2line
+ * subprocess, libbfd) are repeatedly invoked on stripped DSOs.
+ */
+ dso__free_libdw(dso);
+ dso__set_has_srcline(dso, false);
+ ret = 0;
goto out;
}
/* Find source line information for the address. */
dwline = dwfl_module_getsrc(mod, addr + bias);
if (!dwline) {
- ret = -1;
+ /* conclusively missing information -> abort fallbacks */
+ ret = 0;
goto out;
}
@@ -228,7 +243,7 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
free(*file);
*file = NULL;
}
- ret = 0;
+ ret = -ENOMEM;
goto out;
}
@@ -245,7 +260,7 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
*file = NULL;
}
inline_node__clear_frames(node);
- ret = 0;
+ ret = args.err;
goto out;
}
}
diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
index b12094737415..c8f319ce35df 100644
--- a/tools/perf/util/libdw.h
+++ b/tools/perf/util/libdw.h
@@ -23,7 +23,8 @@ struct symbol;
* finds the source line information for the given address, and optionally
* resolves inline function call chains.
*
- * Returns 1 on success (found), 0 on failure (not found).
+ * Returns 1 on success (found), 0 when DWARF/line info is conclusively
+ * missing, and < 0 on initialization or uncompiled error.
*/
int libdw__addr2line(u64 addr, char **file,
unsigned int *line_nr, struct dso *dso,
@@ -47,7 +48,7 @@ static inline int libdw__addr2line(u64 addr __maybe_unused, char **file __maybe_
struct inline_node *node __maybe_unused,
struct symbol *sym __maybe_unused)
{
- return 0;
+ return -1;
}
static inline void dso__free_libdw(struct dso *dso __maybe_unused)
diff --git a/tools/perf/util/llvm-c-helpers.cpp b/tools/perf/util/llvm-c-helpers.cpp
index 004081bd12c9..d990166100f0 100644
--- a/tools/perf/util/llvm-c-helpers.cpp
+++ b/tools/perf/util/llvm-c-helpers.cpp
@@ -50,20 +50,20 @@ static LLVMSymbolizer *get_symbolizer()
return instance;
}
-/* Returns 0 on error, 1 on success. */
+/* Returns < 0 on error, 0 when line info is missing, 1 on success. */
static int extract_file_and_line(const DILineInfo &line_info, char **file,
unsigned int *line)
{
- if (file) {
- if (line_info.FileName == "<invalid>") {
- /* Match the convention of libbfd. */
+ if (line_info.FileName == "<invalid>") {
+ if (file)
*file = nullptr;
- } else {
- /* The caller expects to get something it can free(). */
- *file = strdup(line_info.FileName.c_str());
- if (*file == nullptr)
- return 0;
- }
+ return 0;
+ }
+ if (file) {
+ /* The caller expects to get something it can free(). */
+ *file = strdup(line_info.FileName.c_str());
+ if (*file == nullptr)
+ return -ENOMEM;
}
if (line)
*line = line_info.Line;
@@ -86,30 +86,42 @@ int llvm_addr2line(const char *dso_name, u64 addr,
Expected<DIInliningInfo> res_or_err =
symbolizer->symbolizeInlinedCode(dso_name,
sectioned_addr);
- if (!res_or_err)
- return 0;
+ if (!res_or_err) {
+ consumeError(res_or_err.takeError());
+ return -1;
+ }
unsigned num_frames = res_or_err->getNumberOfFrames();
if (num_frames == 0)
return 0;
- if (extract_file_and_line(res_or_err->getFrame(0),
- file, line) == 0)
- return 0;
+ int ret = extract_file_and_line(res_or_err->getFrame(0),
+ file, line);
+ if (ret <= 0)
+ return ret;
*inline_frames = (llvm_a2l_frame *)calloc(
num_frames, sizeof(**inline_frames));
- if (*inline_frames == nullptr)
- return 0;
+ if (*inline_frames == nullptr) {
+ if (file)
+ zfree(file);
+ return -ENOMEM;
+ }
for (unsigned i = 0; i < num_frames; ++i) {
const DILineInfo &src = res_or_err->getFrame(i);
llvm_a2l_frame &dst = (*inline_frames)[i];
- if (src.FileName == "<invalid>")
- /* Match the convention of libbfd. */
- dst.filename = nullptr;
- else
- dst.filename = strdup(src.FileName.c_str());
+ if (src.FileName == "<invalid>") {
+ for (unsigned j = 0; j < i; ++j) {
+ zfree(&(*inline_frames)[j].filename);
+ zfree(&(*inline_frames)[j].funcname);
+ }
+ zfree(inline_frames);
+ if (file)
+ zfree(file);
+ return 0;
+ }
+ dst.filename = strdup(src.FileName.c_str());
dst.funcname = strdup(src.FunctionName.c_str());
dst.line = src.Line;
@@ -120,7 +132,9 @@ int llvm_addr2line(const char *dso_name, u64 addr,
zfree(&(*inline_frames)[j].funcname);
}
zfree(inline_frames);
- return 0;
+ if (file)
+ zfree(file);
+ return -ENOMEM;
}
}
@@ -131,8 +145,10 @@ int llvm_addr2line(const char *dso_name, u64 addr,
Expected<DILineInfo> res_or_err =
symbolizer->symbolizeCode(dso_name, sectioned_addr);
- if (!res_or_err)
- return 0;
+ if (!res_or_err) {
+ consumeError(res_or_err.takeError());
+ return -1;
+ }
return extract_file_and_line(*res_or_err, file, line);
}
}
diff --git a/tools/perf/util/llvm.c b/tools/perf/util/llvm.c
index 722e71aab100..0ecb1a53359e 100644
--- a/tools/perf/util/llvm.c
+++ b/tools/perf/util/llvm.c
@@ -44,8 +44,11 @@ int llvm__addr2line(const char *dso_name __maybe_unused, u64 addr __maybe_unused
int num_frames = llvm_addr2line(dso_name, addr, file, line,
node && unwind_inlines, &inline_frames);
- if (num_frames == 0 || !inline_frames) {
- /* Error, or we didn't want inlines. */
+ if (num_frames <= 0 || !inline_frames) {
+ /*
+ * Error (< 0 -> iterate fallbacks), missing line info (0), or
+ * we resolved lines without wanting inlines (1).
+ */
return num_frames;
}
@@ -60,8 +63,11 @@ int llvm__addr2line(const char *dso_name __maybe_unused, u64 addr __maybe_unused
inline_frames[i].line);
}
if (inline_list__append(inline_sym, srcline, node) != 0) {
+ if (file)
+ zfree(file);
+ inline_node__clear_frames(node);
free_llvm_inline_frames(inline_frames, num_frames);
- return 0;
+ return -1;
}
}
free_llvm_inline_frames(inline_frames, num_frames);
diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
index a8d16106f619..23951c35fb66 100644
--- a/tools/perf/util/srcline.c
+++ b/tools/perf/util/srcline.c
@@ -181,9 +181,9 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
break;
case A2L_STYLE_UNKNOWN:
default:
- break;
+ return 0;
}
- if (ret > 0)
+ if (ret >= 0)
return ret;
}
@@ -250,6 +250,10 @@ static struct inline_node *addr2inlines(const char *dso_name, u64 addr,
addr2line(dso_name, addr, /*file=*/NULL, /*line_nr=*/NULL, dso,
/*unwind_inlines=*/true, node, sym);
+ if (!dso__has_srcline(dso) && list_empty(&node->val)) {
+ inline_node__delete(node);
+ return NULL;
+ }
return node;
}
@@ -276,8 +280,8 @@ char *__get_srcline(struct dso *dso, u64 addr, struct symbol *sym,
if (dso_name == NULL)
goto out_err;
- if (!addr2line(dso_name, addr, &file, &line, dso,
- unwind_inlines, /*node=*/NULL, sym)) {
+ if (addr2line(dso_name, addr, &file, &line, dso,
+ unwind_inlines, /*node=*/NULL, sym) <= 0) {
free(dso_name);
goto out_err;
}
@@ -302,6 +306,7 @@ char *__get_srcline(struct dso *dso, u64 addr, struct symbol *sym,
dso__set_has_srcline(dso, false);
dso__free_a2l(dso);
dso__free_a2l_libbfd(dso);
+ dso__free_libdw(dso);
}
mutex_unlock(dso__lock(dso));
out:
@@ -331,8 +336,8 @@ char *get_srcline_split(struct dso *dso, u64 addr, unsigned *line)
if (dso_name == NULL)
goto out_err;
- if (!addr2line(dso_name, addr, &file, line, dso, /*unwind_inlines=*/true,
- /*node=*/NULL, /*sym=*/NULL)) {
+ if (addr2line(dso_name, addr, &file, line, dso, /*unwind_inlines=*/true,
+ /*node=*/NULL, /*sym=*/NULL) <= 0) {
free(dso_name);
goto out_err;
}
@@ -350,6 +355,7 @@ char *get_srcline_split(struct dso *dso, u64 addr, unsigned *line)
dso__set_has_srcline(dso, false);
dso__free_a2l(dso);
dso__free_a2l_libbfd(dso);
+ dso__free_libdw(dso);
}
mutex_unlock(dso__lock(dso));
@@ -448,6 +454,9 @@ struct inline_node *dso__parse_addr_inlines(struct dso *dso, u64 addr,
char *dso_name;
struct inline_node *node;
+ if (!dso__has_srcline(dso))
+ return NULL;
+
dso_name = srcline_dso_name(dso);
if (dso_name == NULL)
return NULL;
--
2.56.0.307.g5fe7bd680c-goog
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH 2/3] perf debug: Avoid calling eprintf() in pr_debugN() when verbose < n
2026-10-26 6:50 [PATCH 0/3] perf: Fix libdw addr2line fallback, pr_debugN overhead, and cumulative hist decay Ian Rogers
2026-10-26 6:50 ` [PATCH 1/3] perf libdw: Optimize fallback logic for missing DWARF Ian Rogers
@ 2026-10-26 6:50 ` Ian Rogers
2026-10-26 6:50 ` [PATCH 3/3] perf hist: Do not delete cumulative caller entries before stat_acc decays Ian Rogers
2026-10-27 20:42 ` [PATCH 0/3] perf: Fix libdw addr2line fallback, pr_debugN overhead, and cumulative hist decay Arnaldo Carvalho de Melo
3 siblings, 0 replies; 5+ messages in thread
From: Ian Rogers @ 2026-10-26 6:50 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo, Namhyung Kim, Alireza Haghdoost, Ian Rogers
Cc: Peter Zijlstra, Ingo Molnar, Jiri Olsa, Adrian Hunter,
James Clark, Alessio Podda, Michael Liang, Shimin Guo,
Tanushree Shah, linux-perf-users, linux-kernel
pr_debugN() unconditionally evaluated its arguments and called eprintf() ->
veprintf() before checking if verbose >= n. In hot paths such as
dso__load_sym_internal(), two pr_debug4() calls per symbol accounted for
~15% of total CPU time in 'perf top' even at the default verbose == 0.
Guard eprintf() in pr_debugN() with unlikely(verbose >= (n)) and define
pr_debug() in terms of pr_debugN(1, ...).
In test__parsing_callback() (tools/perf/tests/pmu-events.c), move the
test_generic_metric(mexp, 0) call out of the pr_debug() argument list so
the metric evaluation continues to run during 'perf test' when verbose == 0.
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/tests/pmu-events.c | 5 ++++-
tools/perf/util/debug.h | 5 ++---
2 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/tools/perf/tests/pmu-events.c b/tools/perf/tests/pmu-events.c
index f507ce39439a..e6e4f4cf1fa2 100644
--- a/tools/perf/tests/pmu-events.c
+++ b/tools/perf/tests/pmu-events.c
@@ -906,9 +906,12 @@ static int test__parsing_callback(const struct pmu_metric *pm,
struct metric_expr *mexp;
list_for_each_entry (mexp, &me->head, nd) {
+ double result;
+
if (strcmp(mexp->metric_name, pm->metric_name))
continue;
- pr_debug("Result %f\n", test_generic_metric(mexp, 0));
+ result = test_generic_metric(mexp, 0);
+ pr_debug("Result %f\n", result);
err = 0;
(*failures)--;
goto out_err;
diff --git a/tools/perf/util/debug.h b/tools/perf/util/debug.h
index 6b737e195ce1..7552c9171d90 100644
--- a/tools/perf/util/debug.h
+++ b/tools/perf/util/debug.h
@@ -33,10 +33,9 @@ extern int debug_type_profile;
})
#define pr_info(fmt, ...) \
eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
-#define pr_debug(fmt, ...) \
- eprintf(1, verbose, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_debugN(n, fmt, ...) \
- eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__)
+ (unlikely(verbose >= (n)) ? eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__) : 0)
+#define pr_debug(fmt, ...) pr_debugN(1, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_debug2(fmt, ...) pr_debugN(2, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_debug3(fmt, ...) pr_debugN(3, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_debug4(fmt, ...) pr_debugN(4, pr_fmt(fmt), ##__VA_ARGS__)
--
2.56.0.307.g5fe7bd680c-goog
^ permalink raw reply [flat|nested] 5+ messages in thread