https://gcc.gnu.org/g:479872227c0ac284f3935cafe90c70348059a35c
commit r16-2114-g479872227c0ac284f3935cafe90c70348059a35c
Author: Ian Lance Taylor <i...@golang.org>
Date: Mon Jun 30 21:26:11 2025 -0700
runtime: avoid libc memmove and memclr
The libc memmove and memclr don't reliably operate on full memory words.
We already avoided them on PPC64, but the same problem can occur even
on x86, where some processors use "rep movsb" and "rep stosb".
Always use C code that stores full memory words.
While we're here, clean up the C code. We don't need special handling
if the memmove/memclr pointers are not pointer-aligned.
Unfortunately, this will likely be slower. Perhaps some day we can
have our own assembly code that operates a word at a time,
or we can use different operations when we know there are no pointers.
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/685178
Diff:
---
gcc/go/gofrontend/MERGE | 2 +-
libgo/runtime/go-memclr.c | 41 ++++++++------------
libgo/runtime/go-memmove.c | 94 +++++++++++++++++++---------------------------
3 files changed, 54 insertions(+), 83 deletions(-)
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 64eb27e5e8d1..99bf24c38e09 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-8aab4c94f039132b270ab03968f74d24d315e141
+c4d7bfb9895efc196b04f18f5da77fd99b39212a
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.
diff --git a/libgo/runtime/go-memclr.c b/libgo/runtime/go-memclr.c
index 53b811785392..84df98db6d41 100644
--- a/libgo/runtime/go-memclr.c
+++ b/libgo/runtime/go-memclr.c
@@ -11,50 +11,39 @@ void memclrNoHeapPointers(void *, uintptr)
__attribute__ ((no_split_stack));
void
-memclrNoHeapPointers (void *p1, uintptr len)
+memclrNoHeapPointers(void *p1, uintptr len)
{
-
-#if !defined(__PPC64__)
- __builtin_memset(p1, 0, len);
-#else
- int64 rem,drem,i;
- uint64 offset;
- volatile uint64 *vp;
+ const uintptr ptr_size = sizeof(p1);
+ uintptr rem,drem,i;
+ uintptr offset;
+ volatile uintptr *vp;
if (len == 0) {
return;
}
rem = len;
- offset = (uint64)p1 % 8;
- // This memset is OK since it can't contain
- // an 8 byte aligned pointer.
- if ((rem < 8) || (offset > 0 && offset+rem <= 16)) {
+ offset = (uintptr)p1 % ptr_size;
+ if (rem < ptr_size || offset > 0) {
+ // This memset is OK since it can't contain
+ // an pointer aligned pointer.
__builtin_memset(p1, 0, rem);
return;
}
- // Move initial bytes to get to 8 byte boundary
- if (offset > 0) {
- __builtin_memset(p1, 0, 8-offset);
- p1 = (void*)((char*)p1+8-offset);
- rem -= 8-offset;
- }
- // If at least 8 bytes left, clear
- drem = rem>>3;
+ drem = rem / ptr_size;
- vp = (volatile uint64*)(p1);
+ vp = (volatile uintptr*)(p1);
// Without the use of volatile here, the compiler
// might convert the loop into a memset.
for (i=0; i<drem; i++) {
*vp = 0;
vp++;
- rem -= 8;
+ rem -= ptr_size;
}
- p1 = (void*)((char*)p1 + 8*drem);
- // Clear any remaining
+ // Clear any remaining bytes.
if (rem > 0) {
- __builtin_memset (p1, 0, rem);
+ p1 = (void*)((char*)p1 + ptr_size*drem);
+ __builtin_memset(p1, 0, rem);
}
-#endif
}
diff --git a/libgo/runtime/go-memmove.c b/libgo/runtime/go-memmove.c
index 1ca3f4822b73..1dbd2b392734 100644
--- a/libgo/runtime/go-memmove.c
+++ b/libgo/runtime/go-memmove.c
@@ -12,78 +12,60 @@ void gomemmove(void *, void *, uintptr)
// This implementation is necessary since
// the __builtin_memmove might use __libc_memmove
-// which doesn't require atomicity of 8 byte
+// which doesn't require atomicity of pointer-sized
// moves.
void
-gomemmove (void *dst, void *src, uintptr len)
+gomemmove(void *dst, void *src, uintptr len)
{
-#if !defined(__PPC64__)
- __builtin_memmove(dst, src, len);
-#else
- uint64 offset, tail;
- int64 rem;
- uint64 dwords;
- uint64 i;
- char *bdst,*bsrc;
-
- rem = len;
+ const uintptr ptr_size = sizeof(dst);
+ uintptr tail;
+ uintptr rem;
+ uintptr dwords;
+ uintptr i;
+ char *bdst, *bsrc;
if (len == 0) {
- return;
+ return;
}
- // If src and dst don't have the same 8 byte alignment then
- // there is no issue with copying pointer atomicity. Use the
- // builtin.
- if (((uint64)dst % 8) != ((uint64)src % 8) || len < 8) {
- __builtin_memmove(dst, src, len);
- return;
+ // We expect pointer-containing values to be pointer-aligned.
+ // If these pointers are not aligned, they don't contain pointers.
+ if ((uintptr)dst % ptr_size != 0 || (uintptr)src % ptr_size != 0 || len <
ptr_size) {
+ __builtin_memmove(dst, src, len);
+ return;
}
- // Length >= 8 && same ptr alignment
- offset = (uint64)dst % 8;
-
- // If not 8 byte alignment, move the intial bytes.
- if (offset > 0) {
- __builtin_memmove(dst, src, 8-offset);
- dst += (8-offset);
- src += (8-offset);
- rem -= (8-offset);
- }
+ bdst = (char*)dst;
+ bsrc = (char*)src;
- // Move the tail bytes to make the backward move
- // easier.
- tail = rem % 8;
+ // Move the tail bytes to make the backward move easier.
+ rem = len;
+ tail = rem % ptr_size;
if (tail > 0) {
- __builtin_memmove(dst+rem-tail, src+rem-tail, tail);
- rem -= tail;
- }
-
- if (rem == 0) {
- return;
+ __builtin_memmove(bdst+rem-tail, bsrc+rem-tail, tail);
+ rem -= tail;
}
- // Must now be 8 byte alignment and rem is multiple of 8.
- dwords = len>>3;
+ // Must now be pointer alignment and rem is multiple of ptr_size.
+ dwords = rem / ptr_size;
- // Determine if a backwards move is needed
- // Forward or backward, move all doublewords
+ // Determine if a backwards move is needed.
+ // Forward or backward, move all words.
- if ((uint64)(dst - src) < (uint64)rem) {
- bdst = dst+rem-8;
- bsrc = src+rem-8;
- for (i = 0; i<dwords; i++) {
- *(uint64*)bdst = *(uint64*)bsrc;
- bdst -= 8;
- bsrc -= 8;
- }
+ if ((uintptr)(bdst - bsrc) < rem) {
+ bdst += rem - ptr_size;
+ bsrc += rem - ptr_size;
+ for (i = 0; i<dwords; i++) {
+ *(uintptr*)bdst = *(uintptr*)bsrc;
+ bdst -= ptr_size;
+ bsrc -= ptr_size;
+ }
} else {
- for (i = 0; i<dwords; i++) {
- *(uint64*)dst = *(uint64*)src;
- dst += 8;
- src += 8;
- }
+ for (i = 0; i<dwords; i++) {
+ *(uintptr*)bdst = *(uintptr*)bsrc;
+ bdst += ptr_size;
+ bsrc += ptr_size;
+ }
}
-#endif
}
