[Bug libc/25574] New: wcstombs assertion on __attribute__((__packed__)) structure

[spetrov at mallsi dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25574

            Bug ID: 25574
           Summary: wcstombs assertion on __attribute__((__packed__))
                    structure
           Product: glibc
           Version: 2.27
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: spetrov at mallsi dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Created attachment 12298
  --> https://sourceware.org/bugzilla/attachment.cgi?id=12298&action=edit
wcstombs_test.c source code

Hello,

wcstombs function somehow differ in behavior when used with normal struct {}
and struct {} __attribute__((__packed__));

tested with the following scenario:

-------------------------------------8<-----------------------------

--- gcc version ---
spetrov@HPGLX-LINUX:~$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.4.0-1ubuntu1~18.04.1' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1) 


--- compile ---
spetrov@HPGLX-LINUX:~$ gcc -o wcstombs_test wcstombs_test.c -Wall
-Wstrict-prototypes -Wmissing-prototypes -Werror


--- run program ---
spetrov@HPGLX-LINUX:~$ ./wcstombs_test 
sizeof(struct _test) = 8, sizeof(struct _test_p) = 5
base=0x55f3cc5ba5a0 a1=0x55f3cc5ba5a8, base=0x55f3cc5ba990 a2=0x55f3cc5ba995
wcstombs_test: wcsrtombs.c:94: __wcsrtombs: Assertion `data.__outbuf[-1] ==
'\0'' failed.
Aborted (core dumped)
spetrov@HPGLX-LINUX:~$ 
-------------------------------------8<-----------------------------

source code of wcstombs_test.c is attached.


Kind Regards,
Svetoslav Petrov

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