http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51315
Bug #: 51315
Summary: gcc 4.6.2 miscompilation with -ftree-sra (included in
-O2) on Debian/sparc
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ju...@wooyd.org
Created attachment 25914
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25914
Preprocessed test case code
Hello,
There appears to be a bug in gcc (reproducible with gcc 4.6.2 currently in
Debian unstable), noticed due to Ruby 1.9.x build failures on sparc. The code
gets miscompiled resulting either in bogus results or bus error with -O2,
however the problem goes away when building with -O2 -fno-tree-sra, so tree
optimization is highly suspect. Attached please find a simple standalone case
in preprocessed form, instructions on how to reproduce are included below.
Compiling with -O2, generates broken code:
jurij@debian:~/ftree-sra$ gcc -v -save-temps -g -O2 pack.c -o pack
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/sparc-linux-gnu/4.6/lto-wrapper
Target: sparc-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.2-5'
--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 --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc
--enable-targets=all --with-long-double-128 --enable-checking=release
--build=sparc-linux-gnu --host=sparc-linux-gnu --target=sparc-linux-gnu
Thread model: posix
gcc version 4.6.2 (Debian 4.6.2-5)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-g' '-O2' '-o' 'pack'
'-mcpu=ultrasparc'
/usr/lib/gcc/sparc-linux-gnu/4.6/cc1 -E -quiet -v -imultilib . -imultiarch
sparc-linux-gnu -D__sparc_v9__ pack.c -mcpu=ultrasparc -g -fworking-directory
-O2 -fpch-preprocess -o pack.i
ignoring nonexistent directory "/usr/local/include/sparc-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/sparc-linux-gnu/4.6/../../../../sparc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/sparc-linux-gnu/4.6/include
/usr/local/include
/usr/lib/gcc/sparc-linux-gnu/4.6/include-fixed
/usr/include/sparc-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-g' '-O2' '-o' 'pack'
'-mcpu=ultrasparc'
/usr/lib/gcc/sparc-linux-gnu/4.6/cc1 -fpreprocessed pack.i -quiet -dumpbase
pack.c -mcpu=ultrasparc -auxbase pack -g -O2 -version -o pack.s
GNU C (Debian 4.6.2-5) version 4.6.2 (sparc-linux-gnu)
compiled by GNU C version 4.6.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (Debian 4.6.2-5) version 4.6.2 (sparc-linux-gnu)
compiled by GNU C version 4.6.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 25439f394be45745a7ad849d22cd1d06
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-g' '-O2' '-o' 'pack'
'-mcpu=ultrasparc'
as -s -Av9a -32 -relax -o pack.o pack.s
COMPILER_PATH=/usr/lib/gcc/sparc-linux-gnu/4.6/:/usr/lib/gcc/sparc-linux-gnu/4.6/:/usr/lib/gcc/sparc-linux-gnu/:/usr/lib/gcc/sparc-linux-gnu/4.6/:/usr/lib/gcc/sparc-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/sparc-linux-gnu/4.6/:/usr/lib/gcc/sparc-linux-gnu/4.6/../../../sparc-linux-gnu/:/usr/lib/gcc/sparc-linux-gnu/4.6/../../../../lib/:/lib/sparc-linux-gnu/:/lib/../lib/:/usr/lib/sparc-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/sparc-linux-gnu/4.6/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-g' '-O2' '-o' 'pack'
'-mcpu=ultrasparc'
/usr/lib/gcc/sparc-linux-gnu/4.6/collect2 --build-id --no-add-needed
--eh-frame-hdr -m elf32_sparc -Y P,/usr/lib -dynamic-linker /lib/ld-linux.so.2
-relax -o pack /usr/lib/gcc/sparc-linux-gnu/4.6/../../../sparc-linux-gnu/crt1.o
/usr/lib/gcc/sparc-linux-gnu/4.6/../../../sparc-linux-gnu/crti.o
/usr/lib/gcc/sparc-linux-gnu/4.6/crtbegin.o -L/usr/lib/gcc/sparc-linux-gnu/4.6
-L/usr/lib/gcc/sparc-linux-gnu/4.6/../../../sparc-linux-gnu
-L/usr/lib/gcc/sparc-linux-gnu/4.6/../../../../lib -L/lib/sparc-linux-gnu
-L/lib/../lib -L/usr/lib/sparc-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/sparc-linux-gnu/4.6/../../.. pack.o -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/sparc-linux-gnu/4.6/crtend.o
/usr/lib/gcc/sparc-linux-gnu/4.6/../../../sparc-linux-gnu/crtn.o
jurij@debian:~/ftree-sra$
Resulting binary crashes with a 'bus error':
jurij@debian:~/ftree-sra$ gdb pack
GNU gdb (GDB) 7.3-debian
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "sparc-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/jurij/ftree-sra/pack...done.
(gdb) run
Starting program: /home/jurij/ftree-sra/pack
do_something called with item=-32767
Program received signal SIGBUS, Bus error.
pack_unpack (s=0x1068a "\377\376\035\300", p=0x10692 "") at pack.c:62
62 memcpy (v.a, s, sizeof (int32_t));
(gdb) disass
Dump of assembler code for function pack_unpack:
0x000104a0 <+0>: save %sp, -96, %sp
0x000104a4 <+4>: call 0x207d0 <strlen@plt>
0x000104a8 <+8>: mov %i1, %o0
0x000104ac <+12>: add %i1, %o0, %i5
0x000104b0 <+16>: cmp %i1, %i5
0x000104b4 <+20>: bcs,a %icc, 0x104e0 <pack_unpack+64>
0x000104b8 <+24>: ldub [ %i1 ], %g1
0x000104bc <+28>: rett %i7 + 8
0x000104c0 <+32>: ldsb [ %o0 ], %o0
0x000104c4 <+36>: cmp %g1, 0x73
0x000104c8 <+40>: be,a,pn %icc, 0x10518 <pack_unpack+120>
0x000104cc <+44>: lduh [ %i0 ], %o0
0x000104d0 <+48>: cmp %i1, %i5
0x000104d4 <+52>: be,a,pn %icc, 0x10510 <pack_unpack+112>
0x000104d8 <+56>: ldsb [ %i0 ], %i0
0x000104dc <+60>: ldub [ %i1 ], %g1
0x000104e0 <+64>: sll %g1, 0x18, %g1
0x000104e4 <+68>: sra %g1, 0x18, %g1
0x000104e8 <+72>: cmp %g1, 0x6c
0x000104ec <+76>: bne %icc, 0x104c4 <pack_unpack+36>
0x000104f0 <+80>: inc %i1
=> 0x000104f4 <+84>: ld [ %i0 ], %o0
0x000104f8 <+88>: call 0x10480 <do_something>
0x000104fc <+92>: add %i0, 4, %i0
0x00010500 <+96>: cmp %i1, %i5
0x00010504 <+100>: bne,a %icc, 0x104e0 <pack_unpack+64>
0x00010508 <+104>: ldub [ %i1 ], %g1
0x0001050c <+108>: ldsb [ %i0 ], %i0
0x00010510 <+112>: rett %i7 + 8
0x00010514 <+116>: nop
0x00010518 <+120>: add %i0, 2, %i0
0x0001051c <+124>: sll %o0, 0x10, %o0
0x00010520 <+128>: call 0x10480 <do_something>
0x00010524 <+132>: sra %o0, 0x10, %o0
0x00010528 <+136>: b %xcc, 0x104d4 <pack_unpack+52>
0x0001052c <+140>: cmp %i1, %i5
End of assembler dump.
(gdb) info reg i0
i0 0x1068a 67210
(gdb)
Building with -fno-tree-sra fixes the problem:
jurij@debian:~/ftree-sra$ gcc -g -O2 -fno-tree-sra pack.c -o pack
jurij@debian:~/ftree-sra$ ./pack
do_something called with item=-32767
do_something called with item=-123456
jurij@debian:~/ftree-sra$
This bug is tracked in Debian as http://bugs.debian.org/635126. Please let me
know if you would like any other information.
Thanks.
