[PATCH 1/3] perf dso: Use libbfd to read build_id and .gnu_debuglink section

[Remi Bernon]

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: Remi Bernon <rbernon@xxxxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Jacek Caban <jacek@xxxxxxxxxxxxxxx>
---

As a follow up to https://lkml.org/lkml/2020/6/1/402, I believe the 5.8
merge window is about to close (or is closed?), so I felt like it was
maybe the right time for an update.

This new version includes:
* a few style changes that were previously requested,
* a regression fix where the bfd filename__read_build_id did not return
  the correct size on success,
* a small test case with sample PE file and separate debug file.

Cheers,
Remi

 tools/perf/util/symbol-elf.c | 80 ++++++++++++++++++++++++++++++++++--
 1 file changed, 77 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 5e43054bffea..2489ca5a2284 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
 
@@ -530,6 +532,36 @@ static int elf_read_build_id(Elf *elf, void *bf, size_t size)
 	return err;
 }
 
+#ifdef HAVE_LIBBFD_SUPPORT
+
+int filename__read_build_id(const char *filename, void *bf, size_t size)
+{
+	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 = abfd->build_id->size;
+
+out_close:
+	bfd_close(abfd);
+	return err;
+}
+
+#else
+
 int filename__read_build_id(const char *filename, void *bf, size_t size)
 {
 	int fd, err = -1;
@@ -557,6 +589,8 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 	return err;
 }
 
+#endif
+
 int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
 {
 	int fd, err = -1;
@@ -608,6 +642,44 @@ int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
 	return err;
 }
 
+#ifdef HAVE_LIBBFD_SUPPORT
+
+int filename__read_debuglink(const char *filename, char *debuglink,
+			     size_t size)
+{
+	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 filename__read_debuglink(const char *filename, char *debuglink,
 			     size_t size)
 {
@@ -660,6 +732,8 @@ int filename__read_debuglink(const char *filename, char *debuglink,
 	return err;
 }
 
+#endif
+
 static int dso__swap_init(struct dso *dso, unsigned char eidata)
 {
 	static unsigned int const endian = 1;
-- 
2.27.0