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Fix compilation warning #11
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snappy.cc: In member function ‘void snappy::SnappySinkAllocator::Flush(size_t)’: snappy.cc:1336:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < blocks_.size(); ++i) {
The commit 8bfb028 (Improve zippy decompression speed) introduce a crash when snappy is compiled with _FORTIFY_SOURCE with musl libc. Backtrace reveals that it it comes from using memcpy with overlap, which is undefined behavior. We avoid the undefined behavior due to memcpy with overlap by using a temporary uint64_t. Bactrace from core dump created with `make check`: ```` (gdb) bt #0 memcpy (__n=8, __os=0xb38c8367eea, __od=0xb38c8367eeb) at /usr/include/fortify/string.h:48 google#1 snappy::(anonymous namespace)::UnalignedCopy64 (src=0xb38c8367eea, dst=0xb38c8367eeb) at snappy.cc:92 google#2 0x00006fb4c7c31717 in snappy::(anonymous namespace)::IncrementalCopy ( buf_limit=0xb38c8380ee0 "", op_limit=<optimized out>, op=<optimized out>, src=0xb38c8367eea " .\001") at snappy.cc:178 google#3 snappy::SnappyArrayWriter::AppendFromSelf (len=<optimized out>, offset=<optimized out>, this=<synthetic pointer>) at snappy.cc:1131 google#4 snappy::SnappyDecompressor::DecompressAllTags<snappy::SnappyArrayWriter> ( writer=<synthetic pointer>, this=0x7f1d26737050) at snappy.cc:715 google#5 snappy::InternalUncompressAllTags<snappy::SnappyArrayWriter> ( uncompressed_len=<optimized out>, writer=<synthetic pointer>, decompressor=0x7f1d26737050) at snappy.cc:799 google#6 snappy::InternalUncompress<snappy::SnappyArrayWriter> ( writer=<synthetic pointer>, r=0x7f1d26737000) at snappy.cc:789 google#7 snappy::RawUncompress (compressed=compressed@entry=0x7f1d267370c0, uncompressed=0xb38c8367ee0 " content: .\001") at snappy.cc:1149 google#8 0x00006fb4c7c3194d in snappy::RawUncompress (compressed=<optimized out>, n=<optimized out>, uncompressed=<optimized out>) at snappy.cc:1144 google#9 0x00000b38c5c6261a in snappy::BM_UFlat (iters=99, arg=<optimized out>) at snappy_unittest.cc:1371 google#10 0x00000b38c5c69846 in snappy::Benchmark::Run (this=0xb38c8323c40) at snappy-test.cc:192 google#11 0x00000b38c5c5f3fd in RunSpecifiedBenchmarks () at snappy-test.h:485 google#12 main (argc=1, argv=0x7f1d267374b8) at snappy_unittest.cc:1515 ```` Signed-off-by: Natanael Copa <[email protected]>
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Thanks for ping, but this PR is no longer actual. And nowday there are far more warnings on master than it was in 2015 year, so there should be another solution. |
This warning doesn't shows with current compilation options, but it does when you compile snappy with -Wall flag.