Re: [PATCH] lib: zstd: Mark expected switch fall-throughs

From: Kees Cook
Date: Wed Jan 30 2019 - 02:58:17 EST

On Wed, Jan 30, 2019 at 12:34 PM Gustavo A. R. Silva
<gustavo@xxxxxxxxxxxxxx> wrote:
>
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.
>
> This patch fixes the following warnings:
>
> lib/zstd/bitstream.h:261:30: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/bitstream.h:262:30: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/bitstream.h:263:30: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/bitstream.h:264:30: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/bitstream.h:265:30: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/compress.c:3183:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/decompress.c:1770:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/decompress.c:2376:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/decompress.c:2404:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/decompress.c:2435:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
> lib/zstd/huf_compress.c: In function âHUF_compress1X_usingCTableâ:
> lib/zstd/huf_compress.c:535:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
> if (sizeof((stream)->bitContainer) * 8 < HUF_TABLELOG_MAX * 4 + 7) \
> ^
> lib/zstd/huf_compress.c:558:54: note: in expansion of macro âHUF_FLUSHBITS_2â
> case 3: HUF_encodeSymbol(&bitC, ip[n + 2], CTable); HUF_FLUSHBITS_2(&bitC);
> ^~~~~~~~~~~~~~~
> lib/zstd/huf_compress.c:559:2: note: here
> case 2: HUF_encodeSymbol(&bitC, ip[n + 1], CTable); HUF_FLUSHBITS_1(&bitC);
> ^~~~
> lib/zstd/huf_compress.c:531:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
> if (sizeof((stream)->bitContainer) * 8 < HUF_TABLELOG_MAX * 2 + 7) \
> ^
> lib/zstd/huf_compress.c:559:54: note: in expansion of macro âHUF_FLUSHBITS_1â
> case 2: HUF_encodeSymbol(&bitC, ip[n + 1], CTable); HUF_FLUSHBITS_1(&bitC);
> ^~~~~~~~~~~~~~~
> lib/zstd/huf_compress.c:560:2: note: here
> case 1: HUF_encodeSymbol(&bitC, ip[n + 0], CTable); HUF_FLUSHBITS(&bitC);
> ^~~~
> AR lib/zstd//built-in.a
>
> Warning level 3 was used: -Wimplicit-fallthrough=3
>
> This patch is part of the ongoing efforts to enabling -Wimplicit-fallthrough.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> ---
> lib/zstd/bitstream.h | 5 +++++
> lib/zstd/compress.c | 1 +
> lib/zstd/decompress.c | 5 ++++-
> lib/zstd/huf_compress.c | 2 ++
> 4 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/lib/zstd/bitstream.h b/lib/zstd/bitstream.h
> index a826b99e1d63..3a49784d5c61 100644
> --- a/lib/zstd/bitstream.h
> +++ b/lib/zstd/bitstream.h
> @@ -259,10 +259,15 @@ ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, s
> bitD->bitContainer = *(const BYTE *)(bitD->start);
> switch (srcSize) {
> case 7: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[6]) << (sizeof(bitD->bitContainer) * 8 - 16);
> + /* fall through */
> case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
> + /* fall through */
> case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
> + /* fall through */
> case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
> + /* fall through */
> case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
> + /* fall through */
> case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
> default:;
> }
> diff --git a/lib/zstd/compress.c b/lib/zstd/compress.c
> index f9166cf4f7a9..5e0b67003e55 100644
> --- a/lib/zstd/compress.c
> +++ b/lib/zstd/compress.c
> @@ -3182,6 +3182,7 @@ static size_t ZSTD_compressStream_generic(ZSTD_CStream *zcs, void *dst, size_t *
> zcs->outBuffFlushedSize = 0;
> zcs->stage = zcss_flush; /* pass-through to flush stage */
> }
> + /* fall through */

Perhaps reword the existing comment and move it down?

>
> case zcss_flush: {
> size_t const toFlush = zcs->outBuffContentSize - zcs->outBuffFlushedSize;
> diff --git a/lib/zstd/decompress.c b/lib/zstd/decompress.c
> index b17846725ca0..269ee9a796c1 100644
> --- a/lib/zstd/decompress.c
> +++ b/lib/zstd/decompress.c
> @@ -1768,6 +1768,7 @@ size_t ZSTD_decompressContinue(ZSTD_DCtx *dctx, void *dst, size_t dstCapacity, c
> return 0;
> }
> dctx->expected = 0; /* not necessary to copy more */
> + /* fall through */
>
> case ZSTDds_decodeFrameHeader:
> memcpy(dctx->headerBuffer + ZSTD_frameHeaderSize_prefix, src, dctx->expected);
> @@ -2375,7 +2376,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
> }
> zds->stage = zdss_read;
> }
> - /* pass-through */
> + /* fall through */
>
> case zdss_read: {
> size_t const neededInSize = ZSTD_nextSrcSizeToDecompress(zds->dctx);
> @@ -2404,6 +2405,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
> zds->stage = zdss_load;
> /* pass-through */
> }
> + /* fall through */

Same ("pass-through" exists a couple lines up)

>
> case zdss_load: {
> size_t const neededInSize = ZSTD_nextSrcSizeToDecompress(zds->dctx);
> @@ -2436,6 +2438,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream *zds, ZSTD_outBuffer *output, ZSTD_inB
> /* pass-through */
> }
> }
> + /* fall through */

Same

>
> case zdss_flush: {
> size_t const toFlushSize = zds->outEnd - zds->outStart;
> diff --git a/lib/zstd/huf_compress.c b/lib/zstd/huf_compress.c
> index 40055a7016e6..e727812d12aa 100644
> --- a/lib/zstd/huf_compress.c
> +++ b/lib/zstd/huf_compress.c
> @@ -556,7 +556,9 @@ size_t HUF_compress1X_usingCTable(void *dst, size_t dstSize, const void *src, si
> n = srcSize & ~3; /* join to mod 4 */
> switch (srcSize & 3) {
> case 3: HUF_encodeSymbol(&bitC, ip[n + 2], CTable); HUF_FLUSHBITS_2(&bitC);
> + /* fall through */
> case 2: HUF_encodeSymbol(&bitC, ip[n + 1], CTable); HUF_FLUSHBITS_1(&bitC);
> + /* fall through */
> case 1: HUF_encodeSymbol(&bitC, ip[n + 0], CTable); HUF_FLUSHBITS(&bitC);
> case 0:
> default:;
> --
> 2.20.1
>

Otherwise, yup, looks good.

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

--
Kees Cook