[v4,06/11] perf dso: Add support for reading the e_machine type for a dso

Commit Message

Ian Rogers March 4, 2025, 5:03 a.m. UTC

For ELF file dsos read the e_machine from the ELF header. For kernel
types assume the e_machine matches the perf tool. In other cases
return EM_NONE.

Signed-off-by: Ian Rogers <[e-mail]>
---
 tools/perf/util/dso.c | 54 +++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/dso.h |  1 +
 2 files changed, 55 insertions(+)

Patch

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 5c6e85fdae0d..7f2f1af4f73b 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1170,6 +1170,60 @@  ssize_t dso__data_read_offset(struct dso *dso, struct machine *machine,
 	return data_read_write_offset(dso, machine, offset, data, size, true);
 }
 
+uint16_t dso__e_machine(struct dso *dso, struct machine *machine)
+{
+	uint16_t e_machine = EM_NONE;
+	int fd;
+
+	switch (dso__binary_type(dso)) {
+	case DSO_BINARY_TYPE__KALLSYMS:
+	case DSO_BINARY_TYPE__GUEST_KALLSYMS:
+	case DSO_BINARY_TYPE__VMLINUX:
+	case DSO_BINARY_TYPE__GUEST_VMLINUX:
+	case DSO_BINARY_TYPE__GUEST_KMODULE:
+	case DSO_BINARY_TYPE__GUEST_KMODULE_COMP:
+	case DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE:
+	case DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE_COMP:
+	case DSO_BINARY_TYPE__KCORE:
+	case DSO_BINARY_TYPE__GUEST_KCORE:
+	case DSO_BINARY_TYPE__BPF_PROG_INFO:
+	case DSO_BINARY_TYPE__BPF_IMAGE:
+	case DSO_BINARY_TYPE__OOL:
+	case DSO_BINARY_TYPE__JAVA_JIT:
+		return EM_HOST;
+	case DSO_BINARY_TYPE__DEBUGLINK:
+	case DSO_BINARY_TYPE__BUILD_ID_CACHE:
+	case DSO_BINARY_TYPE__BUILD_ID_CACHE_DEBUGINFO:
+	case DSO_BINARY_TYPE__SYSTEM_PATH_DSO:
+	case DSO_BINARY_TYPE__OPENEMBEDDED_DEBUGINFO:
+	case DSO_BINARY_TYPE__FEDORA_DEBUGINFO:
+	case DSO_BINARY_TYPE__UBUNTU_DEBUGINFO:
+	case DSO_BINARY_TYPE__MIXEDUP_UBUNTU_DEBUGINFO:
+	case DSO_BINARY_TYPE__BUILDID_DEBUGINFO:
+		break;
+	case DSO_BINARY_TYPE__NOT_FOUND:
+	default:
+		return EM_NONE;
+	}
+
+	pthread_mutex_lock(&dso__data_open_lock);
+
+	/*
+	 * dso__data(dso)->fd might be closed if other thread opened another
+	 * file (dso) due to open file limit (RLIMIT_NOFILE).
+	 */
+	try_to_open_dso(dso, machine);
+	fd = dso__data(dso)->fd;
+	if (fd >= 0) {
+		_Static_assert(offsetof(Elf32_Ehdr, e_machine) == 18, "Unexpected offset");
+		_Static_assert(offsetof(Elf64_Ehdr, e_machine) == 18, "Unexpected offset");
+		if (pread(fd, &e_machine, sizeof(e_machine), 18) != sizeof(e_machine))
+			e_machine = EM_NONE;
+	}
+	pthread_mutex_unlock(&dso__data_open_lock);
+	return e_machine;
+}
+
 /**
  * dso__data_read_addr - Read data from dso address
  * @dso: dso object
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index f3ca2a5e7670..ba9b83db061a 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -818,6 +818,7 @@  int dso__data_file_size(struct dso *dso, struct machine *machine);
 off_t dso__data_size(struct dso *dso, struct machine *machine);
 ssize_t dso__data_read_offset(struct dso *dso, struct machine *machine,
 			      u64 offset, u8 *data, ssize_t size);
+uint16_t dso__e_machine(struct dso *dso, struct machine *machine);
 ssize_t dso__data_read_addr(struct dso *dso, struct map *map,
 			    struct machine *machine, u64 addr,
 			    u8 *data, ssize_t size);