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With a char[] flexible array member in a struct with nontrivial alignment, GCC-generated code can access past the end of the array, because GCC assumes there are padding bytes to get the struct aligned. So the common idiom of malloc (offsetof (struct s, m), n) does not properly allocate an n-byte trailing member, as malloc’s argument should be the next multiple of alignof (struct s). See GCC Bug#66661: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66661 Although C11 apparently permits this GCC optimization (i.e., there was a bug in Gnulib not in GCC), possibly this is a defect in C11. See the thread containing: https://gcc.gnu.org/ml/gcc-patches/2016-09/msg00317.html * lib/flexmember.h: New file. * lib/fnmatch.c, lib/fts.c, lib/glob.c, lib/idcache.c: * lib/localename.c, lib/time_rz.c: Include flexmember.h. * lib/fnmatch_loop.c (struct patternlist): * lib/localename.c (struct hash_node): Use FLEXIBLE_ARRAY_MEMBER. * lib/fnmatch_loop.c (EXT): * lib/fts.c (fts_alloc): * lib/glob.c (glob_in_dir): * lib/idcache.c (getuser, getuidbyname, getgroup, getgidbyname): * lib/localename.c (gl_lock_define_initialized): * lib/time_rz.c (tzalloc): Use FLEXSIZEOF instead of offsetof. * m4/flexmember.m4 (AC_C_FLEXIBLE_ARRAY_MEMBER): Check that the size of the struct can be taken. * modules/flexmember (Files): Add lib/flexmember.h. * modules/fnmatch, modules/glob, modules/localename (Depends-on): Add flexmember.
22 lines
223 B
Plaintext
22 lines
223 B
Plaintext
Description:
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Flexible array member support
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Files:
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lib/flexmember.h
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m4/flexmember.m4
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Depends-on:
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configure.ac:
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AC_C_FLEXIBLE_ARRAY_MEMBER
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Makefile.am:
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Include:
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License:
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unlimited
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Maintainer:
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Paul Eggert, Jim Meyering
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