[PATCH] Fix code bloat caused by zcat's seamless magic

[Denys Vlasenko]

Applied, thanks!

On Sat, Jan 7, 2017 at 6:41 PM, Kang-Che Sung <explorer09 at gmail.com> wrote:
> (I discovered this when personally experimenting the make_single_applets script)
>
> This example single-applet configuration would trigger the bloat:
>
>     CONFIG_FEATURE_SEAMLESS_XZ=y
>     CONFIG_FEATURE_SEAMLESS_LZMA=y
>     CONFIG_FEATURE_SEAMLESS_BZ2=y
>     CONFIG_FEATURE_SEAMLESS_GZ=y
>     CONFIG_BUNZIP2=y
>     # CONFIG_ZCAT is not set
>     # All other applets disabled
>
> Here, the resulting "busybox-bunzip2" binary would contain
> unpack_gz_stream, unpack_lzma_stream and unpack_xz_stream functions
> code. In other words, the gzip, lzma and xz decompressors' code are
> linked into the binary unnecessarily.
>
> Fix this by disabling SEAMLESS_MAGIC option flag (setting its value
> to 0) when zcat is disabled. This will help the compiler optimize out
> bbunpack() and no longer generate open_zipped() function call.
>
> Signed-off-by: Kang-Che Sung <explorer09 at gmail.com>
> ---
>  archival/bbunzip.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/archival/bbunzip.c b/archival/bbunzip.c
> index 60a837e22..a8d8a9872 100644
> --- a/archival/bbunzip.c
> +++ b/archival/bbunzip.c
> @@ -25,7 +25,7 @@ enum {
>   OPT_QUIET      = 1 << 3,
>   OPT_DECOMPRESS = 1 << 4,
>   OPT_TEST       = 1 << 5,
> - SEAMLESS_MAGIC = (1 << 31) * SEAMLESS_COMPRESSION,
> + SEAMLESS_MAGIC = (1 << 31) * (ENABLE_ZCAT && SEAMLESS_COMPRESSION),
>  };
>
>  static
> @@ -385,7 +385,7 @@ int gunzip_main(int argc UNUSED_PARAM, char **argv)
>
>   return bbunpack(argv, unpack_gz_stream, make_new_name_gunzip,
> /*unused:*/ NULL);
>  }
> -#endif
> +#endif /* GUNZIP || ZCAT */
>
>
>  /*
> --
> 2.11.0
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