Re: [PATCH v1] perf addr2line: Add a libdw implementation

[James Clark <james.clark@linaro.org>]

On 22/11/2025 9:39 am, Ian Rogers wrote:
> Add an implementation of addr2line that uses libdw. Other addr2line
> implementations or, in the case of forking addr2line, slow. Add an

"are slow"?

Other that that:

Reviewed-by: James Clark <james.clark@linaro.org>

> implementation that caches the libdw information in the dso and uses
> it to find the file and line number information.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>   tools/perf/util/Build     |   1 +
>   tools/perf/util/dso.c     |   2 +
>   tools/perf/util/dso.h     |  11 +++
>   tools/perf/util/libdw.c   | 136 ++++++++++++++++++++++++++++++++++++++
>   tools/perf/util/libdw.h   |  60 +++++++++++++++++
>   tools/perf/util/srcline.c |   5 ++
>   6 files changed, 215 insertions(+)
>   create mode 100644 tools/perf/util/libdw.c
>   create mode 100644 tools/perf/util/libdw.h
> 
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index 1c2a43e1dc68..2bed6274e248 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -224,6 +224,7 @@ perf-util-$(CONFIG_LIBDW) += dwarf-regs-powerpc.o
>   perf-util-$(CONFIG_LIBDW) += dwarf-regs-x86.o
>   perf-util-$(CONFIG_LIBDW) += debuginfo.o
>   perf-util-$(CONFIG_LIBDW) += annotate-data.o
> +perf-util-$(CONFIG_LIBDW) += libdw.o
>   
>   perf-util-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
>   perf-util-$(CONFIG_LOCAL_LIBUNWIND)    += unwind-libunwind-local.o
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 344e689567ee..06980844c014 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -32,6 +32,7 @@
>   #include "string2.h"
>   #include "vdso.h"
>   #include "annotate-data.h"
> +#include "libdw.h"
>   
>   static const char * const debuglink_paths[] = {
>   	"%.0s%s",
> @@ -1605,6 +1606,7 @@ void dso__delete(struct dso *dso)
>   	auxtrace_cache__free(RC_CHK_ACCESS(dso)->auxtrace_cache);
>   	dso_cache__free(dso);
>   	dso__free_a2l(dso);
> +	dso__free_a2l_libdw(dso);
>   	dso__free_symsrc_filename(dso);
>   	nsinfo__zput(RC_CHK_ACCESS(dso)->nsinfo);
>   	mutex_destroy(dso__lock(dso));
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index f8ccb9816b89..4aee23775054 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -268,6 +268,7 @@ DECLARE_RC_STRUCT(dso) {
>   	const char	 *short_name;
>   	const char	 *long_name;
>   	void		 *a2l;
> +	void		 *a2l_libdw;
>   	char		 *symsrc_filename;
>   #if defined(__powerpc__)
>   	void		*dwfl;			/* DWARF debug info */
> @@ -334,6 +335,16 @@ static inline void dso__set_a2l(struct dso *dso, void *val)
>   	RC_CHK_ACCESS(dso)->a2l = val;
>   }
>   
> +static inline void *dso__a2l_libdw(const struct dso *dso)
> +{
> +	return RC_CHK_ACCESS(dso)->a2l_libdw;
> +}
> +
> +static inline void dso__set_a2l_libdw(struct dso *dso, void *val)
> +{
> +	RC_CHK_ACCESS(dso)->a2l_libdw = val;
> +}
> +
>   static inline unsigned int dso__a2l_fails(const struct dso *dso)
>   {
>   	return RC_CHK_ACCESS(dso)->a2l_fails;
> diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
> new file mode 100644
> index 000000000000..c4331fa8e1a3
> --- /dev/null
> +++ b/tools/perf/util/libdw.c
> @@ -0,0 +1,136 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "dso.h"
> +#include "libdw.h"
> +#include "srcline.h"
> +#include "symbol.h"
> +#include "dwarf-aux.h"
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <elfutils/libdwfl.h>
> +
> +void dso__free_a2l_libdw(struct dso *dso)
> +{
> +	Dwfl *dwfl = dso__a2l_libdw(dso);
> +
> +	if (dwfl) {
> +		dwfl_end(dwfl);
> +		dso__set_a2l_libdw(dso, NULL);
> +	}
> +}
> +
> +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)
> +{
> +	static const Dwfl_Callbacks offline_callbacks = {
> +		.find_debuginfo = dwfl_standard_find_debuginfo,
> +		.section_address = dwfl_offline_section_address,
> +		.find_elf = dwfl_build_id_find_elf,
> +	};
> +	Dwfl *dwfl = dso__a2l_libdw(dso);
> +	Dwfl_Module *mod;
> +	Dwfl_Line *dwline;
> +	Dwarf_Addr bias;
> +	const char *src;
> +	int lineno;
> +
> +	if (!dwfl) {
> +		/*
> +		 * Initialize Dwfl session.
> +		 * We need to open the DSO file to report it to libdw.
> +		 */
> +		int fd;
> +
> +		fd = open(dso_name, O_RDONLY);
> +		if (fd < 0)
> +			return 0;
> +
> +		dwfl = dwfl_begin(&offline_callbacks);
> +		if (!dwfl) {
> +			close(fd);
> +			return 0;
> +		}
> +
> +		/*
> +		 * If the report is successful, the file descriptor fd is consumed
> +		 * and closed by the Dwfl. If not, it is not closed.
> +		 */
> +		mod = dwfl_report_offline(dwfl, dso_name, dso_name, fd);
> +		if (!mod) {
> +			dwfl_end(dwfl);
> +			close(fd);
> +			return 0;
> +		}
> +
> +		dwfl_report_end(dwfl, /*removed=*/NULL, /*arg=*/NULL);
> +		dso__set_a2l_libdw(dso, dwfl);
> +	} else {
> +		/* Dwfl session already initialized, get module for address. */
> +		mod = dwfl_addrmodule(dwfl, addr);
> +	}
> +
> +	if (!mod)
> +		return 0;
> +
> +	/* Find source line information for the address. */
> +	dwline = dwfl_module_getsrc(mod, addr);
> +	if (!dwline)
> +		return 0;
> +
> +	/* Get line information. */
> +	src = dwfl_lineinfo(dwline, &addr, &lineno, /*col=*/NULL, /*mtime=*/NULL, /*length=*/NULL);
> +
> +	if (file)
> +		*file = src ? strdup(src) : NULL;
> +	if (line_nr)
> +		*line_nr = lineno;
> +
> +	/* Optionally unwind inline function call chain. */
> +	if (unwind_inlines && node && src) {
> +		Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr, &bias);
> +		Dwarf_Die *scopes = NULL;
> +		int nscopes;
> +
> +		if (!cudie)
> +			return 1;
> +
> +		nscopes = die_get_scopes(cudie, addr, &scopes);
> +		if (nscopes > 0) {
> +			int i;
> +			const char *call_file = src;
> +			unsigned int call_line = lineno;
> +
> +			for (i = 0; i < nscopes; i++) {
> +				Dwarf_Die *die = &scopes[i];
> +				struct symbol *inline_sym;
> +				char *srcline = NULL;
> +				int tag = dwarf_tag(die);
> +
> +				/* We are interested in inlined subroutines. */
> +				if (tag != DW_TAG_inlined_subroutine &&
> +				    tag != DW_TAG_subprogram)
> +					continue;
> +
> +				inline_sym = new_inline_sym(dso, sym, dwarf_diename(die));
> +
> +				if (call_file)
> +					srcline = srcline_from_fileline(call_file, call_line);
> +
> +				inline_list__append(inline_sym, srcline, node);
> +
> +				/* Update call site for next level. */
> +				if (tag == DW_TAG_inlined_subroutine) {
> +					call_file = die_get_call_file(die);
> +					call_line = die_get_call_lineno(die);
> +				} else {
> +					/* Reached the root subprogram. */
> +					break;
> +				}
> +			}
> +			free(scopes);
> +		}
> +	}
> +
> +	return 1;
> +}
> diff --git a/tools/perf/util/libdw.h b/tools/perf/util/libdw.h
> new file mode 100644
> index 000000000000..0f8d7b4a11a5
> --- /dev/null
> +++ b/tools/perf/util/libdw.h
> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef PERF_LIBDW_H
> +#define PERF_LIBDW_H
> +
> +#include <linux/types.h>
> +
> +struct dso;
> +struct inline_node;
> +struct symbol;
> +
> +#ifdef HAVE_LIBDW_SUPPORT
> +/*
> + * libdw__addr2line - Convert address to source location using libdw
> + * @dso_name: Name of the DSO
> + * @addr: Address to resolve
> + * @file: Pointer to return filename (caller must free)
> + * @line_nr: Pointer to return line number
> + * @dso: The dso struct
> + * @unwind_inlines: Whether to unwind inline function calls
> + * @node: Inline node list to append to
> + * @sym: The symbol associated with the address
> + *
> + * This function initializes a Dwfl context for the DSO if not already present,
> + * 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).
> + */
> +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);
> +
> +/*
> + * dso__free_a2l_libdw - Free libdw resources associated with the DSO
> + * @dso: The dso to free resources for
> + *
> + * This function cleans up the Dwfl context used for addr2line lookups.
> + */
> +void dso__free_a2l_libdw(struct dso *dso);
> +
> +#else /* HAVE_LIBDW_SUPPORT */
> +
> +static inline int libdw__addr2line(const char *dso_name __maybe_unused,
> +				   u64 addr __maybe_unused, char **file __maybe_unused,
> +				   unsigned int *line_nr __maybe_unused,
> +				   struct dso *dso __maybe_unused,
> +				   bool unwind_inlines __maybe_unused,
> +				   struct inline_node *node __maybe_unused,
> +				   struct symbol *sym __maybe_unused)
> +{
> +	return 0;
> +}
> +
> +static inline void dso__free_a2l_libdw(struct dso *dso __maybe_unused)
> +{
> +}
> +#endif /* HAVE_LIBDW_SUPPORT */
> +
> +#endif /* PERF_LIBDW_H */
> diff --git a/tools/perf/util/srcline.c b/tools/perf/util/srcline.c
> index 27c0966611ab..4b456c4d4138 100644
> --- a/tools/perf/util/srcline.c
> +++ b/tools/perf/util/srcline.c
> @@ -6,6 +6,7 @@
>   #include "libbfd.h"
>   #include "llvm.h"
>   #include "symbol.h"
> +#include "libdw.h"
>   
>   #include <inttypes.h>
>   #include <string.h>
> @@ -120,6 +121,10 @@ static int addr2line(const char *dso_name, u64 addr, char **file, unsigned int *
>   {
>   	int ret;
>   
> +	ret = libdw__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
> +	if (ret > 0)
> +		return ret;
> +
>   	ret = llvm__addr2line(dso_name, addr, file, line_nr, dso, unwind_inlines, node, sym);
>   	if (ret > 0)
>   		return ret;