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Date: Wed, 12 Jul 2017 05:38:06 +0200 From: Adam Borowski <kilobyte@...band.pl> To: Nick Terrell <terrelln@...com> Cc: "Austin S. Hemmelgarn" <ahferroin7@...il.com>, Kernel Team <Kernel-team@...com>, Chris Mason <clm@...com>, Yann Collet <cyan@...com>, David Sterba <dsterba@...e.cz>, "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 3/4] btrfs: Add zstd support On Tue, Jul 11, 2017 at 06:01:38AM +0000, Nick Terrell wrote: > On 7/10/17, 9:57 PM, "Nick Terrell" <terrelln@...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.
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