Re: [PATCH v2 1/8] perf unwind: Refactor get_entries to allow dynamic libdw/libunwind selection

Ian Rogers
2026-03-31T21:21:18Z

On Tue, Mar 31, 2026 at 1:42 PM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> On Thu, Mar 05, 2026 at 02:19:20PM -0800, Ian Rogers wrote:
> > Currently, both libdw and libunwind define 'unwind__get_entries'. This
> > causes a duplicate symbol build failure when both are compiled into
> > perf.
> >
> > This commit refactors the DWARF unwind post-processing to be
> > configurable at runtime via the .perfconfig file option
> > 'unwind.style', or using the argument '--unwind-style' in the commands
> > 'perf report', 'perf script' and 'perf inject', in a similar manner to
> > the addr2line or the disassembler style.
> >
> > The file 'tools/perf/util/unwind.c' adds the top-level dispatch
> > function 'unwind__get_entries'. The backend implementations are
> > renamed to 'libdw__get_entries' and 'libunwind__get_entries'. Both are
> > attempted as fallbacks if not configured, or if the primary backend
> > fails.
> >
> > Fixes: 2e9191573a69 ("perf build: Remove NO_LIBDW_DWARF_UNWIND option")
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > tools/perf/builtin-inject.c | 4 ++
> > tools/perf/builtin-report.c | 4 ++
> > tools/perf/builtin-script.c | 4 ++
> > tools/perf/util/Build | 1 +
> > tools/perf/util/symbol_conf.h | 15 +++++
> > tools/perf/util/unwind-libdw.c | 2 +-
> > tools/perf/util/unwind-libunwind.c | 2 +-
> > tools/perf/util/unwind.c | 102 +++++++++++++++++++++++++++++
> > tools/perf/util/unwind.h | 40 +++++------
> > 9 files changed, 149 insertions(+), 25 deletions(-)
> > create mode 100644 tools/perf/util/unwind.c
> >
> > diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> > index 5b29f4296861..9ad681b3c0dc 100644
> > --- a/tools/perf/builtin-inject.c
> > +++ b/tools/perf/builtin-inject.c
> > @@ -26,6 +26,7 @@
> > #include "util/synthetic-events.h"
> > #include "util/thread.h"
> > #include "util/namespaces.h"
> > +#include "util/unwind.h"
> > #include "util/util.h"
> > #include "util/tsc.h"
> >
> > @@ -2539,6 +2540,9 @@ int cmd_inject(int argc, const char **argv)
> > OPT_STRING(0, "guestmount", &symbol_conf.guestmount, "directory",
> > "guest mount directory under which every guest os"
> > " instance has a subdir"),
> > + OPT_CALLBACK(0, "unwind-style", NULL, "unwind style",
> > + "unwind styles (libdw,libunwind)",
> > + unwind__option),
> > OPT_BOOLEAN(0, "convert-callchain", &inject.convert_callchain,
> > "Generate callchains using DWARF and drop register/stack data"),
> > OPT_END()
> > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > index 3b81f4b3dc49..ae20c0679990 100644
> > --- a/tools/perf/builtin-report.c
> > +++ b/tools/perf/builtin-report.c
> > @@ -48,6 +48,7 @@
> > #include "util/time-utils.h"
> > #include "util/auxtrace.h"
> > #include "util/units.h"
> > +#include "util/unwind.h"
> > #include "util/util.h" // perf_tip()
> > #include "ui/ui.h"
> > #include "ui/progress.h"
> > @@ -1455,6 +1456,9 @@ int cmd_report(int argc, const char **argv)
> > OPT_CALLBACK(0, "addr2line-style", NULL, "addr2line style",
> > "addr2line styles (libdw,llvm,libbfd,addr2line)",
> > report_parse_addr2line_config),
> > + OPT_CALLBACK(0, "unwind-style", NULL, "unwind style",
> > + "unwind styles (libdw,libunwind)",
> > + unwind__option),
> > OPT_BOOLEAN(0, "demangle", &symbol_conf.demangle,
> > "Symbol demangling. Enabled by default, use --no-demangle to disable."),
> > OPT_BOOLEAN(0, "demangle-kernel", &symbol_conf.demangle_kernel,
> > diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> > index 9f8b0fd27a0a..b6c7c164d02d 100644
> > --- a/tools/perf/builtin-script.c
> > +++ b/tools/perf/builtin-script.c
> > @@ -63,6 +63,7 @@
> > #include <linux/err.h>
> > #include "util/dlfilter.h"
> > #include "util/record.h"
> > +#include "util/unwind.h"
> > #include "util/util.h"
> > #include "util/cgroup.h"
> > #include "util/annotate.h"
> > @@ -4164,6 +4165,9 @@ int cmd_script(int argc, const char **argv)
> > "Enable symbol demangling"),
> > OPT_BOOLEAN(0, "demangle-kernel", &symbol_conf.demangle_kernel,
> > "Enable kernel symbol demangling"),
> > + OPT_CALLBACK(0, "unwind-style", NULL, "unwind style",
> > + "unwind styles (libdw,libunwind)",
> > + unwind__option),
> > OPT_STRING(0, "addr2line", &symbol_conf.addr2line_path, "path",
> > "addr2line binary to use for line numbers"),
> > OPT_STRING(0, "time", &script.time_str, "str",
> > diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> > index bcccad7487a9..6190a8f5b0fa 100644
> > --- a/tools/perf/util/Build
> > +++ b/tools/perf/util/Build
> > @@ -218,6 +218,7 @@ ifndef CONFIG_SETNS
> > perf-util-y += setns.o
> > endif
> >
> > +perf-util-y += unwind.o
> > perf-util-$(CONFIG_LIBDW) += probe-finder.o
> > perf-util-$(CONFIG_LIBDW) += dwarf-aux.o
> > perf-util-$(CONFIG_LIBDW) += dwarf-regs.o
> > diff --git a/tools/perf/util/symbol_conf.h b/tools/perf/util/symbol_conf.h
> > index 71bb17372a6c..25d92bbbfee7 100644
> > --- a/tools/perf/util/symbol_conf.h
> > +++ b/tools/perf/util/symbol_conf.h
> > @@ -9,6 +9,19 @@
> > struct strlist;
> > struct intlist;
> >
> > +enum unwind_style {
> > +
> > + UNWIND_STYLE_UNKNOWN = 0,
> > +
> > + UNWIND_STYLE_LIBDW,
> > +
> > + UNWIND_STYLE_LIBUNWIND,
> > +
> > +};

I'll remove the blank lines in the next version.

> > +
> > +#define MAX_UNWIND_STYLE (UNWIND_STYLE_LIBUNWIND + 1)
> > +
> > +
> > enum a2l_style {
> > A2L_STYLE_UNKNOWN = 0,
> > A2L_STYLE_LIBDW,
> > @@ -80,6 +93,7 @@ struct symbol_conf {
> > *bt_stop_list_str;
> > const char *addr2line_path;
> > enum a2l_style addr2line_style[MAX_A2L_STYLE];
> > + enum unwind_style unwind_style[MAX_UNWIND_STYLE];
> > unsigned long time_quantum;
> > struct strlist *dso_list,
> > *comm_list,
> > @@ -103,3 +117,4 @@ struct symbol_conf {
> > extern struct symbol_conf symbol_conf;
> >
> > #endif // __PERF_SYMBOL_CONF
> > +
> > diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> > index 05e8e68bd49c..d8a5b7d54192 100644
> > --- a/tools/perf/util/unwind-libdw.c
> > +++ b/tools/perf/util/unwind-libdw.c
> > @@ -339,7 +339,7 @@ frame_callback(Dwfl_Frame *state, void *arg)
> > DWARF_CB_ABORT : DWARF_CB_OK;
> > }
> >
> > -int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
> > +int libdw__get_entries(unwind_entry_cb_t cb, void *arg,
> > struct thread *thread,
> > struct perf_sample *data,
> > int max_stack,
> > diff --git a/tools/perf/util/unwind-libunwind.c b/tools/perf/util/unwind-libunwind.c
> > index cb8be6acfb6f..a0016b897dae 100644
> > --- a/tools/perf/util/unwind-libunwind.c
> > +++ b/tools/perf/util/unwind-libunwind.c
> > @@ -79,7 +79,7 @@ void unwind__finish_access(struct maps *maps)
> > ops->finish_access(maps);
> > }
> >
> > -int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
> > +int libunwind__get_entries(unwind_entry_cb_t cb, void *arg,
> > struct thread *thread,
> > struct perf_sample *data, int max_stack,
> > bool best_effort)
> > diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
> > new file mode 100644
> > index 000000000000..9ae7d5ad246d
> > --- /dev/null
> > +++ b/tools/perf/util/unwind.c
> > @@ -0,0 +1,102 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "debug.h"
> > +#include "symbol_conf.h"
> > +#include "unwind.h"
> > +#include <linux/string.h>
> > +#include <string.h>
> > +#include <stdlib.h>
> > +
> > +int unwind__get_entries(unwind_entry_cb_t cb __maybe_unused, void *arg __maybe_unused,
> > + struct thread *thread __maybe_unused,
> > + struct perf_sample *data __maybe_unused,
> > + int max_stack __maybe_unused,
> > + bool best_effort __maybe_unused)
> > +{
> > + int ret = 0;
> > +
> > +#if defined(HAVE_LIBDW_SUPPORT) || defined(HAVE_LIBUNWIND_SUPPORT)
> > + if (symbol_conf.unwind_style[0] == UNWIND_STYLE_UNKNOWN) {
> > + int i = 0;
> > +#ifdef HAVE_LIBDW_SUPPORT
> > + symbol_conf.unwind_style[i++] = UNWIND_STYLE_LIBDW;
> > +#endif
> > +#ifdef HAVE_LIBUNWIND_SUPPORT
> > + symbol_conf.unwind_style[i++] = UNWIND_STYLE_LIBUNWIND;
> > +#endif
> > + }
> > +#endif //defined(HAVE_LIBDW_SUPPORT) || defined(HAVE_LIBUNWIND_SUPPORT)
> > +
> > + for (size_t i = 0; i < ARRAY_SIZE(symbol_conf.unwind_style); i++) {
> > + switch (symbol_conf.unwind_style[i]) {
> > + case UNWIND_STYLE_LIBDW:
> > +#ifdef HAVE_LIBDW_SUPPORT
> > + ret = libdw__get_entries(cb, arg, thread, data, max_stack, best_effort);
> > +#endif
> > + break;
> > + case UNWIND_STYLE_LIBUNWIND:
> > +#ifdef HAVE_LIBUNWIND_SUPPORT
> > + ret = libunwind__get_entries(cb, arg, thread, data, max_stack, best_effort);
> > +#endif
> > + break;
>
>
> What if the user asks for one of the unwinders, symbol_conf.unwind_style
> will be populated with the user's choices, but then here in
> unwind__get_entries() we end up returning 0 because the user choice is
> not built-in?
>
> Also no warning will be emitted that what was asked for is not
> available?
>
> Maybe remove the ifdefs here and have a dummy libdw__get_entries() when
> HAVE_LIBDW_SUPPORT ins't defined that emits the warning and returns -1?
> Ditto for UNWIND_STYLE_LIBUNWIND?

Makes sense, I'll add it to the next version. Since the later patches
are larger I'll wait to address review feedback there before sending
out the next version - this will avoid unnecessary mailing list churn.

Thanks,
Ian

> - Arnaldo
>
> > + case UNWIND_STYLE_UNKNOWN:
> > + default:
> > +#if !defined(HAVE_LIBDW_SUPPORT) && !defined(HAVE_LIBUNWIND_SUPPORT)
> > + pr_warning_once(
> > + "Error: dwarf unwinding not supported, build perf with libdw or libunwind.\n");
> > +#endif
> > + ret = -1;
> > + break;
> > + }
> > + if (ret == 0)
> > + break;
> > + }
> > + return ret;
> > +}
> > +
> > +int unwind__configure(const char *var, const char *value, void *cb __maybe_unused)
> > +{
> > + static const char * const unwind_style_names[] = {
> > + [UNWIND_STYLE_LIBDW] = "libdw",
> > + [UNWIND_STYLE_LIBUNWIND] = "libunwind",
> > + NULL
> > + };
> > + char *s, *p, *saveptr;
> > + size_t i = 0;
> > +
> > + if (strcmp(var, "unwind.style"))
> > + return 0;
> > +
> > + if (!value)
> > + return -1;
> > +
> > + s = strdup(value);
> > + if (!s)
> > + return -1;
> > +
> > + p = strtok_r(s, ",", &saveptr);
> > + while (p && i < ARRAY_SIZE(symbol_conf.unwind_style)) {
> > + bool found = false;
> > + char *q = strim(p);
> > +
> > + for (size_t j = UNWIND_STYLE_LIBDW; j < MAX_UNWIND_STYLE; j++) {
> > + if (!strcasecmp(q, unwind_style_names[j])) {
> > + symbol_conf.unwind_style[i++] = j;
> > + found = true;
> > + break;
> > + }
> > + }
> > + if (!found)
> > + pr_warning("Unknown unwind style: %s\n", q);
> > + p = strtok_r(NULL, ",", &saveptr);
> > + }
> > +
> > + free(s);
> > + return 0;
> > +}
> > +
> > +int unwind__option(const struct option *opt __maybe_unused,
> > + const char *arg,
> > + int unset __maybe_unused)
> > +{
> > + return unwind__configure("unwind.style", arg, NULL);
> > +}
> > diff --git a/tools/perf/util/unwind.h b/tools/perf/util/unwind.h
> > index 9f7164c6d9aa..581d042e170a 100644
> > --- a/tools/perf/util/unwind.h
> > +++ b/tools/perf/util/unwind.h
> > @@ -7,6 +7,7 @@
> > #include "util/map_symbol.h"
> >
> > struct maps;
> > +struct option;
> > struct perf_sample;
> > struct thread;
> >
> > @@ -26,7 +27,9 @@ struct unwind_libunwind_ops {
> > struct perf_sample *data, int max_stack, bool best_effort);
> > };
> >
> > -#ifdef HAVE_DWARF_UNWIND_SUPPORT
> > +int unwind__configure(const char *var, const char *value, void *cb);
> > +int unwind__option(const struct option *opt, const char *arg, int unset);
> > +
> > /*
> > * When best_effort is set, don't report errors and fail silently. This could
> > * be expanded in the future to be more permissive about things other than
> > @@ -36,8 +39,20 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
> > struct thread *thread,
> > struct perf_sample *data, int max_stack,
> > bool best_effort);
> > -/* libunwind specific */
> > +
> > +#ifdef HAVE_LIBDW_SUPPORT
> > +int libdw__get_entries(unwind_entry_cb_t cb, void *arg,
> > + struct thread *thread,
> > + struct perf_sample *data, int max_stack,
> > + bool best_effort);
> > +#endif
> > +
> > #ifdef HAVE_LIBUNWIND_SUPPORT
> > +/* libunwind specific */
> > +int libunwind__get_entries(unwind_entry_cb_t cb, void *arg,
> > + struct thread *thread,
> > + struct perf_sample *data, int max_stack,
> > + bool best_effort);
> > #ifndef LIBUNWIND__ARCH_REG_ID
> > #define LIBUNWIND__ARCH_REG_ID(regnum) libunwind__arch_reg_id(regnum)
> > #endif
> > @@ -57,26 +72,5 @@ static inline int unwind__prepare_access(struct maps *maps __maybe_unused,
> > static inline void unwind__flush_access(struct maps *maps __maybe_unused) {}
> > static inline void unwind__finish_access(struct maps *maps __maybe_unused) {}
> > #endif
> > -#else
> > -static inline int
> > -unwind__get_entries(unwind_entry_cb_t cb __maybe_unused,
> > - void *arg __maybe_unused,
> > - struct thread *thread __maybe_unused,
> > - struct perf_sample *data __maybe_unused,
> > - int max_stack __maybe_unused,
> > - bool best_effort __maybe_unused)
> > -{
> > - return 0;
> > -}
> > -
> > -static inline int unwind__prepare_access(struct maps *maps __maybe_unused,
> > - struct map *map __maybe_unused,
> > - bool *initialized __maybe_unused)
> > -{
> > - return 0;
> > -}
> >
> > -static inline void unwind__flush_access(struct maps *maps __maybe_unused) {}
> > -static inline void unwind__finish_access(struct maps *maps __maybe_unused) {}
> > -#endif /* HAVE_DWARF_UNWIND_SUPPORT */
> > #endif /* __UNWIND_H */
> > --
> > 2.53.0.473.g4a7958ca14-goog