On Tue, Jul 11, 2017 at 06:01:38AM +0000, Nick Terrell wrote:
> On 7/10/17, 9:57 PM, "Nick Terrell" <terre...@fb.com> wrote:
> > The problem is caused by a gcc-7 bug [1]. It miscompiles
> > ZSTD_wildcopy(void *dst, void const *src, ptrdiff_t len) when len is 0.
>
> Sorry, my patch still triggered the gcc bug, I used the wrong compiler.
> This patch works, and runs about the same speed as before the patch for
> small inputs, and slightly faster for larger inputs (100+ bytes). I'll
> look for a faster workaround if benchmarks show it matters.
Confirmed, the fix stops the crash for me. Yay!
> --- a/lib/zstd/zstd_internal.h
> +++ b/lib/zstd/zstd_internal.h
> @@ -139,12 +139,8 @@ static void ZSTD_copy8(void *dst, const void *src) {
> memcpy(dst, src, 8); }
> #define WILDCOPY_OVERLENGTH 8
> ZSTD_STATIC void ZSTD_wildcopy(void *dst, const void *src, ptrdiff_t length)
> {
> - const BYTE *ip = (const BYTE *)src;
> - BYTE *op = (BYTE *)dst;
> - BYTE *const oend = op + length;
> - do
> - COPY8(op, ip)
> - while (op < oend);
> + if (length > 0)
> + memcpy(dst, src, length);
> }
>
> ZSTD_STATIC void ZSTD_wildcopy_e(void *dst, const void *src, void *dstEnd)
> /* should be faster for decoding, but strangely, not verified on all platform
> */
--
⢀⣴⠾⠻⢶⣦⠀
⣾⠁⢠⠒⠀⣿⡁ A dumb species has no way to open a tuna can.
⢿⡄⠘⠷⠚⠋⠀ A smart species invents a can opener.
⠈⠳⣄⠀⠀⠀⠀ A master species delegates.
