Author: mjg
Date: Mon May 7 20:54:42 2018
New Revision: 333332
URL: https://svnweb.freebsd.org/changeset/base/333332
Log:
amd64: fix up memset added in r333324
There was a missing trick expanding the passed pattern to a full word
by multiplication. As a side effect non-zero patterns would be
incorrectly laid down.
This stems from the use of rep stosq which is word-sized, while the passed
argument is byte-sized.
I initially repurposed memcpy into memset without taking this into account.
All but non-bzero testing was performed with a variant utilizing ERMS, i.e.
using only stosb which happens to not into the problem whatsoever. So my bad
twice.
Thanks to Oliver Pinter for noting the problem and providing a testcase.
Modified:
head/sys/amd64/amd64/support.S
Modified: head/sys/amd64/amd64/support.S
==============================================================================
--- head/sys/amd64/amd64/support.S Mon May 7 20:41:24 2018
(r333331)
+++ head/sys/amd64/amd64/support.S Mon May 7 20:54:42 2018
(r333332)
@@ -239,7 +239,8 @@ ENTRY(memset)
PUSH_FRAME_POINTER
movq %rdi,%r9
movq %rdx,%rcx
- movq %rsi,%rax
+ movabs $0x0101010101010101,%rax
+ imulq %rsi,%rax
shrq $3,%rcx
rep
stosq
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