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

Ian Rogers
2025-03-04T05:04:35Z

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 <irogers@google.com>
---
tools/perf/util/dso.c | 54 +++++++++++++++++++++++++++++++++++++++++++
tools/perf/util/dso.h | 1 +
2 files changed, 55 insertions(+)

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);