** Changed in: binutils (Debian)
Status: Unknown => Confirmed
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https://bugs.launchpad.net/bugs/1883880
Title:
fix non-8-bit x86 displacements breaking AVX512 builds on Bionic
Status in binutils package in Ubuntu:
Fix Released
Status in binutils source package in Bionic:
Fix Committed
Status in binutils package in Debian:
Confirmed
Bug description:
[Impact]
* the assembler scales non 8 bit cases which was identified
to break e.g. some AVX512 code. It is nasty as it isn't a compile/link/
time error. Instead the instructions might silently be corrupted until
running. Things might even work on some but fail on other systems if
e.g. the AVX code paths only run on newer chips.
* The fix is upstream for a while and not re-changed again. Furthermore
it is in several Ubuntu releases without bugs due to that, which should
make the backport rather safe.
[Test Case]
* Simple example to trigger the bug:
echo "vmovaps 0x40(,%rax,1),%zmm0" | as --64 -o avx.o && objdump -d
avx.o | grep vmovaps
The expected output is that the objdump output matches the vmovaps
instruction input. When using binutils with the bug, the initial 0x40
will be incorrect.
Working:
$ echo "vmovaps 0x40(,%rax,1),%zmm0" | as --64 -o avx.o && objdump -d avx.o |
grep vmovaps
0: 62 f1 7c 48 28 04 05 vmovaps 0x40(,%rax,1),%zmm0
Failing:
$ echo "vmovaps 0x40(,%rax,1),%zmm0" | as --64 -o avx.o && objdump -d avx.o |
grep vmovaps
0: 62 f1 7c 48 28 04 05 vmovaps 0x1(,%rax,1),%zmm0
[Regression Potential]
* Well, this is a double edged sword. On one hand this is fortunately a
small change and only affects something formerly clearly broken. So it
should be good and only change cases formerly being bad.
But OTOH binutils areused in so many cases that I feel unable to say
"nothing will happen". The change goes to the gnu assembler, so that is
the place to look out for regressions.
[Other Info]
* needs a sponsor experienced with binutils to check potential pitfalls
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Hi,
DPDK has run into some issues in the past
https://bugs.dpdk.org/show_bug.cgi?id=97
https://bugs.dpdk.org/show_bug.cgi?id=249
Eventually the issues got resolved in binutils via
https://sourceware.org/bugzilla/show_bug.cgi?id=23465
After binutils is fixed people rebuilding DPDK themselve can use
http://patches.dpdk.org/patch/71679/
to gain more performance while on Bionics bintuils level.
Note: Bionic is on DPDK 17.11.x which will not get further stable release
afaik. But quite often people build their own DPDK. In fact this came up as a
request from Openvswitch upstream/Intel to allow such builds on Bionic.
I'd ping those people about the bug and ask them to participate in the
verification if this becomes an SRU.
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