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libgo: ensure memmove, memset 8 byte atomicity on ppc64x
Go requires that pointer moves are done 8 bytes at a time, but gccgo uses libc's memmove and memset which does not require that, and there are some cases where an 8 byte move might be done as 4+4. To enforce 8 byte moves for memmove and memset, this adds a C implementation in libgo/runtime for memmove and memset to be used on ppc64le and ppc64. Asm implementations were considered but discarded to avoid different implementations for different target ISAs. Fixes golang/go#41428 Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/294931
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| Original file line number | Diff line number | Diff line change |
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| @@ -1,4 +1,4 @@ | ||
| 78a840e4940159a66072237f6b002ab79f441b79 | ||
| 56cf388da8d04bbd3824c4df34d77a8afa69749b | ||
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| The first line of this file holds the git revision number of the last | ||
| merge done from the gofrontend repository. |
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| @@ -0,0 +1,89 @@ | ||
| /* go-memmove.c -- memmove | ||
| Copyright 2021 The Go Authors. All rights reserved. | ||
| Use of this source code is governed by a BSD-style | ||
| license that can be found in the LICENSE file. */ | ||
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| #include "runtime.h" | ||
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| void gomemmove(void *, void *, uintptr) | ||
| __asm__ (GOSYM_PREFIX "runtime.memmove") | ||
| __attribute__ ((no_split_stack)); | ||
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| // This implementation is necessary since | ||
| // the __builtin_memmove might use __libc_memmove | ||
| // which doesn't require atomicity of 8 byte | ||
| // moves. | ||
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| void | ||
| 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; | ||
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| rem = len; | ||
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| if (len == 0) { | ||
| return; | ||
| } | ||
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| // 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; | ||
| } | ||
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| // Length >= 8 && same ptr alignment | ||
| offset = (uint64)dst % 8; | ||
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| // 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); | ||
| } | ||
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| // Move the tail bytes to make the backward move | ||
| // easier. | ||
| tail = rem % 8; | ||
| if (tail > 0) { | ||
| __builtin_memmove(dst+rem-tail, src+rem-tail, tail); | ||
| rem -= tail; | ||
| } | ||
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| if (rem == 0) { | ||
| return; | ||
| } | ||
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| // Must now be 8 byte alignment and rem is multiple of 8. | ||
| dwords = len>>3; | ||
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| // Determine if a backwards move is needed | ||
| // Forward or backward, move all doublewords | ||
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| 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; | ||
| } | ||
| } else { | ||
| for (i = 0; i<dwords; i++) { | ||
| *(uint64*)dst = *(uint64*)src; | ||
| dst += 8; | ||
| src += 8; | ||
| } | ||
| } | ||
| #endif | ||
| } |
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