svn commit: r333332 - head/sys/amd64/amd64

[Mateusz Guzik]

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