[Bug target/59444] New: [4.6.3 32-bit] Character buffers on stack not aligned on a 4-byte boundary.

[Bug target/59444] New: [4.6.3 32-bit] Character buffers on stack not aligned on a 4-byte boundary.

[vasiliy.v.buzoverya at intel dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59444

            Bug ID: 59444
           Summary: [4.6.3 32-bit] Character buffers on stack not aligned
                    on a 4-byte boundary.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vasiliy.v.buzoverya at intel dot com

Created attachment 31408
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31408&action=edit
Preprocessed file that triggers the bug.

4.6.3 on Ubuntu 12.04 32-bit.

A function has two character buffers on stack(of 5 and 10 bytes in size). The
addresses of the buffers won't get aligned on a 4-byte boundary even if the
-mpreferred-stack-boundary=2 compilation option is specified. The addresses of
the buffers are odd values, e.g. 0xbffff17f and 0xbffff175.

Here's a snippet of assembler code:
   0x080483e4 <+0>:    push   %ebp
   0x080483e5 <+1>:    mov    %esp,%ebp
   0x080483e7 <+3>:    sub    $0x20,%esp
   0x080483ea <+6>:    lea    -0x9(%ebp),%eax
   ...
   0x08048403 <+31>:    lea    -0x13(%ebp),%eax
   ...



Build log:


Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.6/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --enable-targets=all --disable-werror
--with-arch-32=i686 --with-tune=generic --enable-checking=release
--build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-O0'
'-mpreferred-stack-boundary=2' '-fno-stack-protector' '-mtune=generic'
'-march=i686'
 /usr/lib/gcc/i686-linux-gnu/4.6/cc1 -E -quiet -v -imultilib . -imultiarch
i386-linux-gnu example.c -mpreferred-stack-boundary=2 -mtune=generic
-march=i686 -Wall -Wextra -fno-stack-protector -O0 -fpch-preprocess -o
example.i
ignoring nonexistent directory "/usr/local/include/i386-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/i686-linux-gnu/4.6/../../../../i686-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/i686-linux-gnu/4.6/include
 /usr/local/include
 /usr/lib/gcc/i686-linux-gnu/4.6/include-fixed
 /usr/include/i386-linux-gnu
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-O0'
'-mpreferred-stack-boundary=2' '-fno-stack-protector' '-mtune=generic'
'-march=i686'
 /usr/lib/gcc/i686-linux-gnu/4.6/cc1 -fpreprocessed example.i -quiet -dumpbase
example.c -mpreferred-stack-boundary=2 -mtune=generic -march=i686 -auxbase
example -O0 -Wall -Wextra -version -fno-stack-protector -o example.s
GNU C (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (i686-linux-gnu)
    compiled by GNU C version 4.6.3, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=63 --param ggc-min-heapsize=63477
GNU C (Ubuntu/Linaro 4.6.3-1ubuntu5) version 4.6.3 (i686-linux-gnu)
    compiled by GNU C version 4.6.3, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=63 --param ggc-min-heapsize=63477
Compiler executable checksum: 09c248eab598b9e2acb117da4cdbd785
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-O0'
'-mpreferred-stack-boundary=2' '-fno-stack-protector' '-mtune=generic'
'-march=i686'
 as --32 -o example.o example.s
COMPILER_PATH=/usr/lib/gcc/i686-linux-gnu/4.6/:/usr/lib/gcc/i686-linux-gnu/4.6/:/usr/lib/gcc/i686-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/4.6/:/usr/lib/gcc/i686-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i686-linux-gnu/4.6/:/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/4.6/../../../../lib/:/lib/i386-linux-gnu/:/lib/../lib/:/usr/lib/i386-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/i686-linux-gnu/4.6/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-O0'
'-mpreferred-stack-boundary=2' '-fno-stack-protector' '-mtune=generic'
'-march=i686'
 /usr/lib/gcc/i686-linux-gnu/4.6/collect2 --sysroot=/ --build-id
--no-add-needed --as-needed --eh-frame-hdr -m elf_i386 --hash-style=gnu
-dynamic-linker /lib/ld-linux.so.2 -z relro
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/crt1.o
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/crti.o
/usr/lib/gcc/i686-linux-gnu/4.6/crtbegin.o -L/usr/lib/gcc/i686-linux-gnu/4.6
-L/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu
-L/usr/lib/gcc/i686-linux-gnu/4.6/../../../../lib -L/lib/i386-linux-gnu
-L/lib/../lib -L/usr/lib/i386-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/i686-linux-gnu/4.6/../../.. example.o -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/i686-linux-gnu/4.6/crtend.o
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/crtn.o

[Bug target/59444] [4.6.3 32-bit] Character buffers on stack not aligned on a 4-byte boundary.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59444

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
That's not what the option ensures.  If you want the buffers to be aligned
say so via a aligned(4) attribute.