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* [Bug c/38052]  New: genautomata segfaults when -O2 is enabled
@ 2008-11-07 15:33 r0bertz at gentoo dot org
  2008-11-07 15:42 ` [Bug c/38052] " r0bertz at gentoo dot org
                   ` (10 more replies)
  0 siblings, 11 replies; 12+ messages in thread
From: r0bertz at gentoo dot org @ 2008-11-07 15:33 UTC (permalink / raw)
  To: gcc-bugs

I have done some detailed research on this problem. It is after the needed
information. Please do have a look.

The source is checked out on 2008-11-07

The system is using O32 abi.

The configure option is
var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/configure
--cache-file=./config.cache --with-stabs --prefix=/usr
--bindir=/usr/mipsel-unknown-linux-gnu/gcc-bin/4.4.0-pre9999
--includedir=/usr/lib/gcc/mipsel-unknown-linux-gnu/4.4.0-pre9999/include
--datadir=/usr/share/gcc-data/mipsel-unknown-linux-gnu/4.4.0-pre9999
--mandir=/usr/share/gcc-data/mipsel-unknown-linux-gnu/4.4.0-pre9999/man
--infodir=/usr/share/gcc-data/mipsel-unknown-linux-gnu/4.4.0-pre9999/info
--with-gxx-include-dir=/usr/lib/gcc/mipsel-unknown-linux-gnu/4.4.0-pre9999/include/g++-v4
--disable-altivec --disable-fixed-point --enable-nls --without-included-gettext
--with-system-zlib --disable-checking --disable-werror --enable-secureplt
--disable-multilib --enable-libmudflap --disable-libssp --disable-libgomp
--enable-cld --disable-libgcj --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu
--with-bugurl=http://bugs.gentoo.org/ --with-pkgversion= --enable-linux-futex
--enable-languages=c,c++ --program-transform-name=s,y,y,
--build=mipsel-unknown-linux-gnu --host=mipsel-unknown-linux-gnu
--target=mipsel-unknown-linux-gnu
--srcdir=/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc
--with-build-libsubdir=.

The command to build genautomata is:
/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/build/./prev-gcc/xgcc
-B/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/build/./prev-gcc/
-B/usr/mipsel-unknown-linux-gnu/bin/ -c  -O2 -g -pipe -DIN_GCC   -W -Wall
-Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wcast-qual
-Wold-style-definition -Wc++-compat -Wmissing-format-attribute -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings   -DHAVE_CONFIG_H
-DGENERATOR_FILE -I. -Ibuild
-I/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc
-I/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/build
-I/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/../include
-I/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/../libcpp/include

-I/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/../libdecnumber
-I/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/../libdecnumber/dpd
-I../libdecnumber  -DCLOOG_PPL_BACKEND   -o build/genautomata.o
/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/genautomata.c
/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/build/./prev-gcc/xgcc
-B/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/build/./prev-gcc/
-B/usr/mipsel-unknown-linux-gnu/bin/  -O2 -g -pipe -DIN_GCC   -W -Wall
-Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wcast-qual
-Wold-style-definition -Wc++-compat -Wmissing-format-attribute -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings   -DHAVE_CONFIG_H
-DGENERATOR_FILE  -o build/genautomata \
            build/genautomata.o build/rtl.o build/read-rtl.o build/ggc-none.o
build/vec.o build/min-insn-modes.o build/gensupport.o build/print-rtl.o
build/errors.o .././libiberty/libiberty.a -lm

The command segfaulted:
build/genautomata
/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/gcc/config/mips/mips.md
insn-conditions.md


I have debugged this executable with gdb. And I found the exact instruction
which caused the segfaults. It has something to do with the manipulation of $gp
register.

>From readelf -a genautomata, the Canonical gp value of Primary GOT: 00440090

Normally before calling an function, the gp register must be loaded with this
value. This can be observed it compiled with no optimization option.

However if -O2 is enabled, the following code in genautomata.c:
6975   fprintf (output_file, "static const ");
6976   output_range_type (output_file, 0, automaton->insn_equiv_classes_num);
6977   fprintf (output_file, " ");
6978   output_translate_vect_name (output_file, automaton);
becomes(this is generated with -S option):
        lw      $28,16($sp)
        lw      $7,%lo(output_file)($17)
        lw      $25,%call16(fwrite)($28)
        lui     $4,%hi($LC171)
        addiu   $4,$4,%lo($LC171)
        li      $5,1                    # 0x1
        jalr    $25
        li      $6,13                   # 0xd

        lw      $6,16($18)
        lw      $4,%lo(output_file)($17)
        .option pic0
        jal     output_range_type
        .option pic2
        move    $5,$0

        lw      $28,16($sp)
        lw      $5,%lo(output_file)($17)
        lw      $25,%call16(fputc)($28)
        nop
        jalr    $25
        li      $4,32                   # 0x20

        lw      $4,%lo(output_file)($17)
        .option pic0
        jal     output_translate_vect_name
        .option pic2
        move    $5,$18
We can see there is no "lw      $28,16($sp)" before "jal     output_range_type"
or "jal     output_translate_vect_name"

In the case of output_range_type, there is no problem, because inside the
function, the only access to GOT is to find "fwrite"'s GOT entry. And the entry
already contains the resolved address, since immediately before the call to
output_range_type, there is a call to fwrite.

The problem with output_translate_vect_name is this function has two calls to
fprintf, and they are called for the first time in this program. So we need to
call the lazy resolver. And that's exactly where the program segfaults. Since
gp's value is incorrect, neither will be the resolver's address.

That's what I have got so far. Hope this could help to solve the problem.


-- 
           Summary: genautomata segfaults when -O2 is enabled
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: r0bertz at gentoo dot org
 GCC build triplet: mipsel-unknown-linux-gnu
  GCC host triplet: mipsel-unknown-linux-gnu
GCC target triplet: mipsel-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38052


^ permalink raw reply	[flat|nested] 12+ messages in thread
end of thread, other threads:[~2008-11-16 21:10 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-11-07 15:33 [Bug c/38052] New: genautomata segfaults when -O2 is enabled r0bertz at gentoo dot org
2008-11-07 15:42 ` [Bug c/38052] " r0bertz at gentoo dot org
2008-11-10 22:46 ` [Bug target/38052] [4.4 Regression] " pinskia at gcc dot gnu dot org
2008-11-12  1:02 ` kumba at gentoo dot org
2008-11-13  9:54 ` r0bertz at gentoo dot org
2008-11-13 11:38 ` r0bertz at gentoo dot org
2008-11-13 17:28 ` r0bertz at gentoo dot org
2008-11-13 17:35 ` ebotcazou at gcc dot gnu dot org
2008-11-15 20:43 ` rsandifo at gcc dot gnu dot org
2008-11-16 20:28 ` rsandifo at gcc dot gnu dot org
2008-11-16 20:34 ` rsandifo at gcc dot gnu dot org
2008-11-16 21:10 ` rsandifo at gcc dot gnu dot org

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