We already have logic in our Huffman encoder to validate Huffman tables with missing symbols.
We use this for higher compression levels to re-use the previous blocks statistics, or when the dictionaries table has zero-weighted symbols.
This check was leftover as an oversight from before we added validation for Huffman tables.
I validated that the `dictionary_loader` fuzzer has coverage of every line in the `ZSTD_loadCEntropy()` function to validate that it is correctly testing this function.
MSAN is hooked into the system malloc, but when the user provides a custom
allocator, it may not provide the same cleansing behavior. So if we leave
memory poisoned and return it to the user's allocator, where it is re-used
elsewhere, our poisoning can blow up in some other context.
They are Linux-like environments under Windows and have all the tools needed to support staged installation and testing.
Beware: this only affects the make build system.
For some reasons when LTO is enabled, the compiler complains about statbuf variable not being correctly initialized, even though the variable has an assert != NULL just few lines below (FIO_getDictFileStat)
This is the fixed build failure:
x86_64-linux-gnu-gcc -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security -fdebug-prefix-map=/<<PKGBUILDDIR>>=/usr/src/libzstd-1.5.5+dfsg2-1 -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow -Wstrict-aliasing=1 -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wundef -Wpointer-arith -Wvla -Wformat=2 -Winit-self -Wfloat-equal -Wwrite-strings -Wredundant-decls -Wmissing-prototypes -Wc++-compat -g -Werror -Wa,--noexecstack -Wdate-time -D_FORTIFY_SOURCE=2 -DXXH_NAMESPACE=ZSTD_ -DDEBUGLEVEL=1 -DZSTD_LEGACY_SUPPORT=5 -DZSTD_MULTITHREAD -DZSTD_GZCOMPRESS -DZSTD_GZDECOMPRESS -DZSTD_LZMACOMPRESS -DZSTD_LZMADECOMPRESS -DZSTD_LZ4COMPRESS -DZSTD_LZ4DECOMPRESS -DZSTD_LEGACY_SUPPORT=5 -c -MT obj/conf_086c46a51a716b674719b8acb8484eb8/zstdcli_trace.o -MMD -MP -MF obj/conf_086c46a51a716b674719b8acb8484eb8/zstdcli_trace.d -o obj/conf_086c46a51a716b674719b8acb8484eb8/zstdcli_trace.o zstdcli_trace.c
In function ‘UTIL_isRegularFileStat’,
inlined from ‘UTIL_getFileSizeStat’ at util.c:524:10,
inlined from ‘FIO_createDResources’ at fileio.c:2230:30:
util.c:209:12: error: ‘statbuf.st_mode’ may be used uninitialized [-Werror=maybe-uninitialized]
209 | return S_ISREG(statbuf->st_mode) != 0;
| ^
fileio.c: In function ‘FIO_createDResources’:
fileio.c:2223:12: note: ‘statbuf’ declared here
2223 | stat_t statbuf;
| ^
lto1: all warnings being treated as errors
The sequence section starts with a number, which tells how sequences are present in the section.
If this number if 0, the section automatically ends.
The number 0 can be represented using the 1 byte or the 2 bytes formats.
That's because the 2-bytes formats fully overlaps the 1 byte format.
However, when 0 is represented using the 2-bytes format,
the decoder was expecting the sequence section to continue,
and was looking for FSE tables, which is incorrect.
Fixed this behavior, in both the reference decoder and the educational behavior.
In practice, this behavior never happens,
because the encoder will always select the 1-byte format to represent 0,
since this is more efficient.
Completed the fix with a new golden sample for tests,
a clarification of the specification,
and a decoder errata paragraph.
