perf symbols: Save DSO loading errno to better report errors

Before, when some problem happened while trying to load the kernel
symtab, 'perf top' would show:

      ┌─Warning:───────────────────────────┐
      │The vmlinux file can't be used.     │
      │Kernel samples will not be resolved.│
      │                                    │
      │                                    │
      │Press any key...                    │
      └────────────────────────────────────┘

Now, it reports:

  # perf top --vmlinux /dev/null

      ┌─Warning:───────────────────────────────────────────┐
      │The /tmp/passwd file can't be used: Invalid ELF file│
      │Kernel samples will not be resolved.                │
      │                                                    │
      │                                                    │
      │Press any key...                                    │
      └────────────────────────────────────────────────────┘

This is possible because we now register the reason for not being able
to load the symtab in the dso->load_errno member, and provide a
dso__strerror_load() routine to format this error into a strerror like
string with a short reason for the error while loading.

That can be just forwarding the dso__strerror_load() call to
strerror_r(), or, for a separate errno range providing a custom message.

Reported-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-u5rb5uq63xqhkfb8uv2lxd5u@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 27 insertions, 10 deletions

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 78ffde9df9bf..476268c99431 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -595,10 +595,13 @@ static int decompress_kmodule(struct dso *dso, const char *name,
 		return -1;
 
 	fd = mkstemp(tmpbuf);
-	if (fd < 0)
+	if (fd < 0) {
+		dso->load_errno = errno;
 		goto out;
+	}
 
 	if (!decompress_to_file(m.ext, name, fd)) {
+		dso->load_errno = DSO_LOAD_ERRNO__DECOMPRESSION_FAILURE;
 		close(fd);
 		fd = -1;
 	}
@@ -635,37 +638,49 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
 	Elf *elf;
 	int fd;
 
-	if (dso__needs_decompress(dso))
+	if (dso__needs_decompress(dso)) {
 		fd = decompress_kmodule(dso, name, type);
-	else
+		if (fd < 0)
+			return -1;
+	} else {
 		fd = open(name, O_RDONLY);
-
-	if (fd < 0)
-		return -1;
+		if (fd < 0) {
+			dso->load_errno = errno;
+			return -1;
+		}
+	}
 
 	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
 	if (elf == NULL) {
 		pr_debug("%s: cannot read %s ELF file.\n", __func__, name);
+		dso->load_errno = DSO_LOAD_ERRNO__INVALID_ELF;
 		goto out_close;
 	}
 
 	if (gelf_getehdr(elf, &ehdr) == NULL) {
+		dso->load_errno = DSO_LOAD_ERRNO__INVALID_ELF;
 		pr_debug("%s: cannot get elf header.\n", __func__);
 		goto out_elf_end;
 	}
 
-	if (dso__swap_init(dso, ehdr.e_ident[EI_DATA]))
+	if (dso__swap_init(dso, ehdr.e_ident[EI_DATA])) {
+		dso->load_errno = DSO_LOAD_ERRNO__INTERNAL_ERROR;
 		goto out_elf_end;
+	}
 
 	/* Always reject images with a mismatched build-id: */
 	if (dso->has_build_id) {
 		u8 build_id[BUILD_ID_SIZE];
 
-		if (elf_read_build_id(elf, build_id, BUILD_ID_SIZE) < 0)
+		if (elf_read_build_id(elf, build_id, BUILD_ID_SIZE) < 0) {
+			dso->load_errno = DSO_LOAD_ERRNO__CANNOT_READ_BUILDID;
 			goto out_elf_end;
+		}
 
-		if (!dso__build_id_equal(dso, build_id))
+		if (!dso__build_id_equal(dso, build_id)) {
+			dso->load_errno = DSO_LOAD_ERRNO__MISMATCHING_BUILDID;
 			goto out_elf_end;
+		}
 	}
 
 	ss->is_64_bit = (gelf_getclass(elf) == ELFCLASS64);
@@ -701,8 +716,10 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
 	}
 
 	ss->name   = strdup(name);
-	if (!ss->name)
+	if (!ss->name) {
+		dso->load_errno = errno;
 		goto out_elf_end;
+	}
 
 	ss->elf    = elf;
 	ss->fd     = fd;