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authorJames Clark <james.clark@arm.com>2021-09-06 18:22:38 +0300
committerArnaldo Carvalho de Melo <acme@redhat.com>2021-09-27 15:32:28 +0300
commit0f892fd1bd29a25a62c236c5d4f942ee3295ef49 (patch)
tree4cbe132a8c97a47a1054e992fab0abfbfb1fec1d /tools/perf
parent5c34aea341b16e29fde6e6c8d4b18866cd99754d (diff)
downloadlinux-0f892fd1bd29a25a62c236c5d4f942ee3295ef49.tar.xz
perf tests: Fix flaky test 'Object code reading'
This test occasionally fails on aarch64 when a sample is taken in free@plt and it fails with "Bytes read differ from those read by objdump". This is because that symbol is near a section boundary in the elf file. Despite the -z option to always output zeros, objdump uses bfd_map_over_sections() to iterate through the elf file so it doesn't see outside of the sections where these zeros are and can't print them. For example this boundary proceeds free@plt in libc with a gap of 48 bytes between .plt and .text: objdump -d -z --start-address=0x23cc8 --stop-address=0x23d08 libc-2.30.so libc-2.30.so: file format elf64-littleaarch64 Disassembly of section .plt: 0000000000023cc8 <*ABS*+0x7fd00@plt+0x8>: 23cc8: 91018210 add x16, x16, #0x60 23ccc: d61f0220 br x17 Disassembly of section .text: 0000000000023d00 <abort@@GLIBC_2.17-0x98>: 23d00: a9bf7bfd stp x29, x30, [sp, #-16]! 23d04: 910003fd mov x29, sp Taking a sample in free@plt is very rare because it is so small, but the test can be forced to fail almost every time on any platform by linking the test with a shared library that has a single empty function and calling it in a loop. The fix is to zero the buffers so that when there is a jump in the addresses output by objdump, zeros are already filled in between. Signed-off-by: James Clark <james.clark@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Namhyung Kim <namhyung@kernel.org> Link: http://lore.kernel.org/lkml/20210906152238.3415467-1-james.clark@arm.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf')
-rw-r--r--tools/perf/tests/code-reading.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
index 9866cddebf23..9b4a765e4b73 100644
--- a/tools/perf/tests/code-reading.c
+++ b/tools/perf/tests/code-reading.c
@@ -229,8 +229,8 @@ static int read_object_code(u64 addr, size_t len, u8 cpumode,
struct thread *thread, struct state *state)
{
struct addr_location al;
- unsigned char buf1[BUFSZ];
- unsigned char buf2[BUFSZ];
+ unsigned char buf1[BUFSZ] = {0};
+ unsigned char buf2[BUFSZ] = {0};
size_t ret_len;
u64 objdump_addr;
const char *objdump_name;