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| author | Austin Clements <austin@google.com> | 2015-10-02 18:17:54 -0400 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2015-11-13 17:26:39 +0000 |
| commit | fc0f36b2ce201142a9137fa8ea6a55e454d1213f (patch) | |
| tree | 25626da0d5ae1ad6de8d128eb99f8a232832884b | |
| parent | 9f59bc85a2c9932caebf0b6c6a282a0e839d62af (diff) | |
| download | go-fc0f36b2ce201142a9137fa8ea6a55e454d1213f.tar.gz go-fc0f36b2ce201142a9137fa8ea6a55e454d1213f.zip | |
[release-branch.go1.5] runtime: use 4 byte writes in amd64p32 memmove/memclr
Currently, amd64p32's memmove and memclr use 8 byte writes as much as
possible and 1 byte writes for the tail of the object. However, if an
object ends with a 4 byte pointer at an 8 byte aligned offset, this
may copy/zero the pointer field one byte at a time, allowing the
garbage collector to observe a partially copied pointer.
Fix this by using 4 byte writes instead of 8 byte writes.
Updates #12552.
Change-Id: I13324fd05756fb25ae57e812e836f0a975b5595c
Reviewed-on: https://go-review.googlesource.com/15370
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-on: https://go-review.googlesource.com/16908
Reviewed-by: Russ Cox <rsc@golang.org>
| -rw-r--r-- | src/runtime/asm_amd64p32.s | 6 | ||||
| -rw-r--r-- | src/runtime/memmove_nacl_amd64p32.s | 23 |
2 files changed, 16 insertions, 13 deletions
diff --git a/src/runtime/asm_amd64p32.s b/src/runtime/asm_amd64p32.s index 6e97256c70..a001a764e7 100644 --- a/src/runtime/asm_amd64p32.s +++ b/src/runtime/asm_amd64p32.s @@ -627,12 +627,12 @@ TEXT runtime·memclr(SB),NOSPLIT,$0-8 MOVL ptr+0(FP), DI MOVL n+4(FP), CX MOVQ CX, BX - ANDQ $7, BX - SHRQ $3, CX + ANDQ $3, BX + SHRQ $2, CX MOVQ $0, AX CLD REP - STOSQ + STOSL MOVQ BX, CX REP STOSB diff --git a/src/runtime/memmove_nacl_amd64p32.s b/src/runtime/memmove_nacl_amd64p32.s index 373607afec..be9e1e55be 100644 --- a/src/runtime/memmove_nacl_amd64p32.s +++ b/src/runtime/memmove_nacl_amd64p32.s @@ -4,6 +4,9 @@ #include "textflag.h" +// This could use MOVSQ, but we use MOVSL so that if an object ends in +// a 4 byte pointer, we copy it as a unit instead of byte by byte. + TEXT runtime·memmove(SB), NOSPLIT, $0-12 MOVL to+0(FP), DI MOVL from+4(FP), SI @@ -14,9 +17,9 @@ TEXT runtime·memmove(SB), NOSPLIT, $0-12 forward: MOVL BX, CX - SHRL $3, CX - ANDL $7, BX - REP; MOVSQ + SHRL $2, CX + ANDL $3, BX + REP; MOVSL MOVL BX, CX REP; MOVSB RET @@ -32,13 +35,13 @@ back: STD MOVL BX, CX - SHRL $3, CX - ANDL $7, BX - SUBL $8, DI - SUBL $8, SI - REP; MOVSQ - ADDL $7, DI - ADDL $7, SI + SHRL $2, CX + ANDL $3, BX + SUBL $4, DI + SUBL $4, SI + REP; MOVSL + ADDL $3, DI + ADDL $3, SI MOVL BX, CX REP; MOVSB CLD |