Messages in this thread | | | Date | Fri, 24 Sep 2021 15:53:35 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf tests: Fix flaky test 'Object code reading' |
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Em Mon, Sep 06, 2021 at 04:22:38PM +0100, James Clark escreveu: > 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.
Thanks, applied.
- Arnaldo
> 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
--
- Arnaldo
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