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flac: Work around gcc bug to prevent false unset MD5 signature warning

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A bug beginning in gcc version 9.2 causes strings to get incorrectly
stripped when passed directly to memcmp with a zero first byte (1).
This bug causes flac -t to fail on any .flac file with a md5 checksum
beginning in 00. To work around this bug, the FLAC__byte type is used
for an empty md5 sum to prevent a string from being stripped, which
is backwards compatible and avoids compile-time checks. This was
initially reported back in March 2020, but has seen more light since
Ubuntu 19.10 and up ship with gcc 9.2 as the default compiler. A
patch has been merged into the master gcc branch (2), but has not
been included in any versions as of this commit date.

The initial reporter provided a patch in their bug report (3), which
is included in this PR with authorship attributed to the reporter.

(1) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95189
(2) https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=d5803b9876b3d11c93d1a10fabb3fbb1c4a14bd6
(3) https://sourceforge.net/p/flac/bugs/478/

Closes #192.
This commit is contained in:
NotTsunami
2020-09-04 11:31:58 -04:00
committed by Erik de Castro Lopo
parent d7b33142ec
commit 5f5035d209
1 changed files with 2 additions and 1 deletions
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3
src/flac/decode.c
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@@ -1305,9 +1305,10 @@ void metadata_callback(const FLAC__StreamDecoder *decoder, const FLAC__StreamMet
FLAC__stream_decoder_get_decode_position(decoder, &decoder_session->decode_position);
if(metadata->type == FLAC__METADATA_TYPE_STREAMINFO) {
FLAC__byte emptyMD5[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
FLAC__uint64 skip, until;
decoder_session->got_stream_info = true;
decoder_session->has_md5sum = memcmp(metadata->data.stream_info.md5sum, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16);
decoder_session->has_md5sum = memcmp(metadata->data.stream_info.md5sum, emptyMD5, 16);
decoder_session->bps = metadata->data.stream_info.bits_per_sample;
decoder_session->channels = metadata->data.stream_info.channels;
decoder_session->sample_rate = metadata->data.stream_info.sample_rate;