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runtime: do not use memmove in the Plan 9 signal handler 

Fixes a regression introduced in revision 4cb93e2900d0.

That revision changed runtime·memmove to use SSE MOVOU
instructions for sizes between 17 and 256 bytes. We were
using memmove to save a copy of the note string during
the note handler. The Plan 9 kernel does not allow the
use of floating point in note handlers (which includes
MOVOU since it touches the XMM registers).

Arguably, runtime·memmove should not be using MOVOU when
GO386=387 but that wouldn't help us on amd64. It's very
important that we guard against any future changes so we
use a simple copy loop instead.

This change is extracted from CL 9796043 (since that CL
is still being ironed out).

R=rsc
CC=golang-dev
https://golang.org/cl/34640045
This commit is contained in:
Anthony Martin 2013-12-09 18:41:48 -05:00 committed by Russ Cox
parent dba4d11e08
commit 274a8e3f56
2 changed files with 24 additions and 12 deletions
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18
src/pkg/runtime/os_plan9_386.c
View File

@ -59,12 +59,18 @@ runtime·sighandler(void *v, int8 *s, G *gp)
if(gp == nil || m->notesig == 0)
goto Throw;
// Save error string from sigtramp's stack,
// into gsignal->sigcode0, so we can reliably
// access it from the panic routines.
if(len > ERRMAX)
len = ERRMAX;
runtime·memmove((void*)m->notesig, (void*)s, len);
// Copy the error string from sigtramp's stack into m->notesig so
// we can reliably access it from the panic routines. We can't use
// runtime·memmove here since it will use SSE instructions for big
// copies. The Plan 9 kernel doesn't allow floating point in note
// handlers.
//
// TODO(ality): revert back to memmove when the kernel is fixed.
if(len >= ERRMAX)
len = ERRMAX-1;
for(i = 0; i < len; i++)
m->notesig[i] = s[i];
m->notesig[i] = '\0';
gp->sig = i;
gp->sigpc = ureg->pc;

18
src/pkg/runtime/os_plan9_amd64.c
View File

@ -67,12 +67,18 @@ runtime·sighandler(void *v, int8 *s, G *gp)
if(gp == nil || m->notesig == 0)
goto Throw;
// Save error string from sigtramp's stack,
// into gsignal->sigcode0, so we can reliably
// access it from the panic routines.
if(len > ERRMAX)
len = ERRMAX;
runtime·memmove((void*)m->notesig, (void*)s, len);
// Copy the error string from sigtramp's stack into m->notesig so
// we can reliably access it from the panic routines. We can't use
// runtime·memmove here since it will use SSE instructions for big
// copies. The Plan 9 kernel doesn't allow floating point in note
// handlers.
//
// TODO(ality): revert back to memmove when the kernel is fixed.
if(len >= ERRMAX)
len = ERRMAX-1;
for(i = 0; i < len; i++)
m->notesig[i] = s[i];
m->notesig[i] = '\0';
gp->sig = i;
gp->sigpc = ureg->ip;