From: James Clark <james.clark@arm.com>
To: acme@kernel.org, linux-perf-users@vger.kernel.org
Cc: James Clark <james.clark@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
linux-kernel@vger.kernel.org
Subject: [PATCH] perf tests: Fix flaky test 'Object code reading'
Date: Mon, 6 Sep 2021 16:22:38 +0100 [thread overview]
Message-ID: <20210906152238.3415467-1-james.clark@arm.com> (raw)
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>
---
tools/perf/tests/code-reading.c | 4 ++--
1 file 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;
--
2.28.0
next reply other threads:[~2021-09-06 15:22 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-06 15:22 James Clark [this message]
2021-09-24 18:53 ` [PATCH] perf tests: Fix flaky test 'Object code reading' Arnaldo Carvalho de Melo
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