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

Arnaldo Carvalho de Melo
2026-03-31T20:42:37Z

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,
> +
> +};
> +
> +#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?

- 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