* [PATCH v1 1/2] perf libdw: Pass dso_name explicitly to properly anchor split-debug builds
2026-08-24 6:28 [PATCH v1 0/2] perf libdw: Improve split-debug handling and error fallback Ian Rogers
@ 2026-08-24 6:28 ` Ian Rogers
2026-08-24 6:28 ` [PATCH v1 2/2] perf libdw: Optimize fallback logic for missing DWARF Ian Rogers
1 sibling, 0 replies; 3+ messages in thread
From: Ian Rogers @ 2026-08-24 6:28 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark,
Tanushree Shah, Michael Liang, Alessio Podda, Shimin Guo,
linux-perf-users, linux-kernel
When resolving source lines via get_srcline(), srcline_dso_name()
explicitly checks for and returns the split-debug file path
(dso__symsrc_filename, which is cached during dso__load()) rather than
the default executable path (dso__long_name). Because libdw__addr2line
defaulted to dso__long_name without accepting a passed dso_name, the
Dwfl_Module was hardcoded to initialize against the stripped
executable instead of the intended split debug file.
By explicitly passing the successfully resolved dso_name down the call
path from addr2line() to dso__libdw_dwfl(), libdw accurately anchors to
the dynamically discovered split-debug file, fixing dwarf resolution for
these binaries.
Assisted-by: Antigravity:gemini-3.6-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/arch/powerpc/util/skip-callchain-idx.c | 2 +-
tools/perf/util/dso.h | 5 +++--
tools/perf/util/libdw.c | 10 +++++-----
tools/perf/util/libdw.h | 5 +++--
tools/perf/util/srcline.c | 2 +-
5 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
index e57f10798fa6..f7dd27faaec2 100644
--- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
@@ -152,7 +152,7 @@ static int check_return_addr(struct dso *dso, Dwarf_Addr mapped_pc)
Dwarf_Addr end = mapped_pc;
bool signalp;
- dwfl = dso__libdw_dwfl(dso);
+ dwfl = dso__libdw_dwfl(dso, NULL);
if (!dwfl)
return -1;
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 55c4aaa53c38..3271e1ecaa9e 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -380,9 +380,10 @@ static inline void dso__set_libdw(struct dso *dso, void *val)
struct Dwfl;
#ifdef HAVE_LIBDW_SUPPORT
-struct Dwfl *dso__libdw_dwfl(struct dso *dso);
+struct Dwfl *dso__libdw_dwfl(struct dso *dso, const char *dso_name);
#else
-static inline struct Dwfl *dso__libdw_dwfl(struct dso *dso __maybe_unused)
+static inline struct Dwfl *dso__libdw_dwfl(struct dso *dso __maybe_unused,
+ const char *dso_name __maybe_unused)
{
return NULL;
}
diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
index 4ca7e7e4fbe9..f53caee980b0 100644
--- a/tools/perf/util/libdw.c
+++ b/tools/perf/util/libdw.c
@@ -25,17 +25,17 @@ void dso__free_libdw(struct dso *dso)
}
}
-struct Dwfl *dso__libdw_dwfl(struct dso *dso)
+struct Dwfl *dso__libdw_dwfl(struct dso *dso, const char *dso_name)
{
Dwfl *dwfl = dso__libdw(dso);
- const char *dso_name;
Dwfl_Module *mod;
int fd;
if (dwfl)
return dwfl;
- dso_name = dso__long_name(dso);
+ if (!dso_name)
+ dso_name = dso__long_name(dso);
/*
* Initialize Dwfl session.
* We need to open the DSO file to report it to libdw.
@@ -163,11 +163,11 @@ static int libdw_a2l_cb(Dwarf_Die *die, void *_args)
return DWARF_CB_ABORT;
}
-int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
+int libdw__addr2line(const char *dso_name, u64 addr, char **file, unsigned int *line_nr,
struct dso *dso, bool unwind_inlines,
struct inline_node *node, struct symbol *sym)
{
- Dwfl *dwfl = dso__libdw_dwfl(dso);
+ Dwfl *dwfl = dso__libdw_dwfl(dso, dso_name);
Dwfl_Module *mod;
Dwfl_Line *dwline;
Dwarf_Addr bias;
diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
index b12094737415..4bdd28d44e25 100644
--- a/tools/perf/util/libdw.h
+++ b/tools/perf/util/libdw.h
@@ -25,7 +25,7 @@ struct symbol;
*
* Returns 1 on success (found), 0 on failure (not found).
*/
-int libdw__addr2line(u64 addr, char **file,
+int libdw__addr2line(const char *dso_name, u64 addr, char **file,
unsigned int *line_nr, struct dso *dso,
bool unwind_inlines, struct inline_node *node,
struct symbol *sym);
@@ -40,7 +40,8 @@ void dso__free_libdw(struct dso *dso);
#else /* HAVE_LIBDW_SUPPORT */
-static inline int libdw__addr2line(u64 addr __maybe_unused, char **file __maybe_unused,
+static inline int libdw__addr2line(const char *dso_name, u64 addr __maybe_unused,
+ char **file __maybe_unused,
unsigned int *line_nr __maybe_unused,
struct dso *dso __maybe_unused,
bool unwind_inlines __maybe_unused,
diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
index b082178c279b..8e954f0c860a 100644
--- a/tools/perf/util/srcline.c
+++ b/tools/perf/util/srcline.c
@@ -155,7 +155,7 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
for (size_t i = 0; i < ARRAY_SIZE(symbol_conf.addr2line_style); i++) {
switch (symbol_conf.addr2line_style[i]) {
case A2L_STYLE_LIBDW:
- ret = libdw__addr2line(addr, file, line_nr, dso, unwind_inlines,
+ ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines,
node, sym);
break;
case A2L_STYLE_LLVM:
--
2.55.0.766.g2966f0265a-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH v1 2/2] perf libdw: Optimize fallback logic for missing DWARF
2026-08-24 6:28 [PATCH v1 0/2] perf libdw: Improve split-debug handling and error fallback Ian Rogers
2026-08-24 6:28 ` [PATCH v1 1/2] perf libdw: Pass dso_name explicitly to properly anchor split-debug builds Ian Rogers
@ 2026-08-24 6:28 ` Ian Rogers
1 sibling, 0 replies; 3+ messages in thread
From: Ian Rogers @ 2026-08-24 6:28 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark,
Tanushree Shah, Michael Liang, Alessio Podda, Shimin Guo,
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() falls back immediately with 0. This causes perf's
addr2line_style loop to fall back to launching the cmd__addr2line()
sub-process wrapper. In environments generating massive numbers of
unmapped traces, this forces thousands of redundant `addr2line -e`
fork/execs in a polling loop.
This patch intercepts failure scenarios:
1. Returns -1 when dwfl_module_getsrc() returns NULL (meaning the DWARF
is parsed but the line mapping is natively missing).
2. Evaluates `ret < 0` in addr2line() to dynamically bypass the subprocess
fallback and return 0. This precisely acts as a failure condition,
incrementing the dso->a2l_fails counter and accurately triggering the
A2L_FAIL_LIMIT throttling without shelling out.
3. Incorporates exact error string checking for "no DWARF" to safely
abort alternative fallbacks directly within both libdw resolving and
the unwinder logic (unwind-libdw).
This preserves fallbacks if unwinder or DWARF parsing genuinely
aborts, but avoids falling back when mappings are absent.
Assisted-by: Antigravity:gemini-3.6-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/libdw.c | 11 +++++++++--
tools/perf/util/srcline.c | 2 ++
tools/perf/util/unwind-libdw.c | 15 ++++++++++++---
3 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
index f53caee980b0..7c681b03c654 100644
--- a/tools/perf/util/libdw.c
+++ b/tools/perf/util/libdw.c
@@ -186,8 +186,15 @@ int libdw__addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
* between the regular ELF addr2line addresses and those to use with
* libdw.
*/
- if (!dwfl_module_getdwarf(mod, &bias))
- return 0;
+ if (!dwfl_module_getdwarf(mod, &bias)) {
+ const char *err = dwfl_errmsg(-1);
+
+ /*
+ * Abort fallbacks specifically when DWARF is completely missing,
+ * but allow alternative backends to try if parsing failed.
+ */
+ return (err && strstr(err, "no DWARF")) ? -1 : 0;
+ }
/* Find source line information for the address. */
dwline = dwfl_module_getsrc(mod, addr + bias);
diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
index 8e954f0c860a..8283a741c018 100644
--- a/tools/perf/util/srcline.c
+++ b/tools/perf/util/srcline.c
@@ -176,6 +176,8 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
}
if (ret > 0)
return ret;
+ if (ret < 0)
+ return 0;
}
return 0;
diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index 63a5c2253174..69d4585c870c 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -441,8 +441,17 @@ int libdw__get_entries(unwind_entry_cb_t cb, void *arg,
}
out:
- if (err)
- pr_debug("unwind: failed with '%s'\n", dwfl_errmsg(-1));
+ if (err) {
+ const char *msg = dwfl_errmsg(-1);
+
+ pr_debug("unwind: failed with '%s'\n", msg);
+ /*
+ * Abort fallbacks specifically when unwinding information is completely
+ * missing, but allow fallback unwinders to try if parsing simply failed.
+ */
+ if (msg && strstr(msg, "no DWARF"))
+ err = -EINVAL;
+ }
for (i = 0; i < ui->idx; i++)
map_symbol__exit(&ui->entries[i].ms);
@@ -460,6 +469,6 @@ int libdw__get_entries(unwind_entry_cb_t cb, void *arg,
* < 0 : fatal error (e.g. -ENOMEM). Aborts unwinding entirely.
*/
if (err)
- return (err == -ENOMEM) ? -ENOMEM : (entries > 0 ? 1 : 0);
+ return (err == -ENOMEM || err == -EINVAL) ? err : (entries > 0 ? 1 : 0);
return entries;
}
--
2.55.0.766.g2966f0265a-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread