linux-kernel - [RFC PATCH 1/2] perf dso: Use libbfd to read build_id and .gnu

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Message-Id: <20200601111915.114974-2-rbernon@codeweavers.com>
Date:   Mon,  1 Jun 2020 13:19:14 +0200
From:   Rémi Bernon <rbernon@...eweavers.com>
To:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Rémi Bernon <rbernon@...eweavers.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Jacek Caban <jacek@...eweavers.com>
Subject: [RFC PATCH 1/2] perf dso: Use libbfd to read build_id and .gnu_debuglink section

Wine generates PE binaries for most of its modules and perf is unable
to parse these files to get build_id or .gnu_debuglink section.

Using libbfd when available, instead of libelf, makes it possible to
resolve debug file location regardless of the dso binary format.

Signed-off-by: Rémi Bernon <rbernon@...eweavers.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Jacek Caban <jacek@...eweavers.com>
---
 tools/perf/util/symbol-elf.c | 65 ++++++++++++++++++++++++++++++++++--
 1 file changed, 62 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index be5b493f8284..85bbc1ec9fe5 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -50,6 +50,10 @@ typedef Elf64_Nhdr GElf_Nhdr;
 #define DMGL_ANSI        (1 << 1)       /* Include const, volatile, etc */
 #endif
 
+#ifdef HAVE_LIBBFD_SUPPORT
+#define PACKAGE 'perf'
+#include <bfd.h>
+#else
 #ifdef HAVE_CPLUS_DEMANGLE_SUPPORT
 extern char *cplus_demangle(const char *, int);
 
@@ -65,9 +69,7 @@ static inline char *bfd_demangle(void __maybe_unused *v,
 {
 	return NULL;
 }
-#else
-#define PACKAGE 'perf'
-#include <bfd.h>
+#endif
 #endif
 #endif
 
@@ -532,6 +534,30 @@ static int elf_read_build_id(Elf *elf, void *bf, size_t size)
 
 int filename__read_build_id(const char *filename, void *bf, size_t size)
 {
+#ifdef HAVE_LIBBFD_SUPPORT
+	int err = -1;
+	bfd *abfd;
+
+	abfd = bfd_openr(filename, NULL);
+	if (!abfd)
+		return -1;
+
+	if (!bfd_check_format(abfd, bfd_object)) {
+		pr_debug2("%s: cannot read %s bfd file.\n", __func__, filename);
+		goto out_close;
+	}
+
+	if (!abfd->build_id || abfd->build_id->size > size)
+		goto out_close;
+
+	memcpy(bf, abfd->build_id->data, abfd->build_id->size);
+	memset(bf + abfd->build_id->size, 0, size - abfd->build_id->size);
+	err = 0;
+
+out_close:
+	bfd_close(abfd);
+	return err;
+#else
 	int fd, err = -1;
 	Elf *elf;
 
@@ -555,6 +581,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 	close(fd);
 out:
 	return err;
+#endif
 }
 
 int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
@@ -611,6 +638,37 @@ int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
 int filename__read_debuglink(const char *filename, char *debuglink,
 			     size_t size)
 {
+#ifdef HAVE_LIBBFD_SUPPORT
+	int err = -1;
+	asection *section;
+	bfd *abfd;
+
+	abfd = bfd_openr(filename, NULL);
+	if (!abfd)
+		return -1;
+
+	if (!bfd_check_format(abfd, bfd_object)) {
+		pr_debug2("%s: cannot read %s bfd file.\n", __func__, filename);
+		goto out_close;
+	}
+
+	section = bfd_get_section_by_name(abfd, ".gnu_debuglink");
+	if (!section)
+		goto out_close;
+
+	if (section->size > size)
+		goto out_close;
+
+	if (!bfd_get_section_contents(abfd, section, debuglink, 0,
+				      section->size))
+		goto out_close;
+
+	err = 0;
+
+out_close:
+	bfd_close(abfd);
+	return err;
+#else
 	int fd, err = -1;
 	Elf *elf;
 	GElf_Ehdr ehdr;
@@ -658,6 +716,7 @@ int filename__read_debuglink(const char *filename, char *debuglink,
 	close(fd);
 out:
 	return err;
+#endif
 }
 
 static int dso__swap_init(struct dso *dso, unsigned char eidata)
-- 
2.26.1