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* [Bug tree-optimization/50337] New: -ftree-dse performs wrong elimination on electric-fence
@ 2011-09-08 17:06 cjwatson at ubuntu dot com
  2011-09-08 17:08 ` [Bug tree-optimization/50337] " cjwatson at ubuntu dot com
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: cjwatson at ubuntu dot com @ 2011-09-08 17:06 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50337

             Bug #: 50337
           Summary: -ftree-dse performs wrong elimination on
                    electric-fence
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: cjwatson@ubuntu.com


Using built-in specs.
COLLECT_GCC=/usr/bin/gcc-4.6.real
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.6.1/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.6.1-9ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++,go --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-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 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu2)

$ gcc -O2 -g -Wall efence.i -lpthread
efence.c: In function ‘stringErrorReport’:
efence.c:944:2: warning: return makes pointer from integer without a cast
[enabled by default]
efence.c: In function ‘vprint’:
efence.c:1135:5: warning: ignoring return value of ‘write’, declared with
attribute warn_unused_result [-Wunused-result]
efence.c:1156:6: warning: ignoring return value of ‘write’, declared with
attribute warn_unused_result [-Wunused-result]
efence.c:1165:12: warning: ignoring return value of ‘write’, declared with
attribute warn_unused_result [-Wunused-result]
efence.c:1178:6: warning: ignoring return value of ‘write’, declared with
attribute warn_unused_result [-Wunused-result]
efence.c:1189:4: warning: ignoring return value of ‘write’, declared with
attribute warn_unused_result [-Wunused-result]
efence.c: In function ‘printNumber’:
efence.c:1119:8: warning: ignoring return value of ‘write’, declared with
attribute warn_unused_result [-Wunused-result]
$ ./a.out
iteration 0: size 29

  Electric Fence 2.1 Copyright (C) 1987-1998 Bruce Perens.
[...]
iteration 233: size 9007
Segmentation fault (core dumped)

(The exact number of iterations may vary.  Since this is entering infinite
recursion, you might want to have a ulimit in place if trying this out.)

In gdb, I can see that the problem is that internalUse is not set to 1 in the
allocateMoreSlots function while recursively calling malloc, and indeed that
assignment has been optimised out:

(gdb) disas /rm memalign
[...]
418     static void
419     allocateMoreSlots(void)
420     {
421             size_t  newSize = allocationListSize + bytesPerPage;
   0x080498b3 <+627>:   a1 94 c0 04 08  mov    0x804c094,%eax
   0x080498b8 <+632>:   8b 3d 8c c0 04 08       mov    0x804c08c,%edi
   0x080498c8 <+648>:   01 c7   add    %eax,%edi

422             void *  newAllocation;
423             void *  oldAllocation = allocationList;
   0x080498be <+638>:   8b 35 88 c0 04 08       mov    0x804c088,%esi

424
425             Page_AllowAccess(allocationList, allocationListSize);
   0x080498c4 <+644>:   89 44 24 04     mov    %eax,0x4(%esp)
   0x080498ca <+650>:   89 34 24        mov    %esi,(%esp)
   0x080498cd <+653>:   e8 be f5 ff ff  call   0x8048e90 <Page_AllowAccess>

426             noAllocationListProtection = 1;
427             internalUse = 1;
428
429             newAllocation = malloc(newSize);
   0x080498d2 <+658>:   89 3c 24        mov    %edi,(%esp)
   0x080498d5 <+661>:   e8 86 fb ff ff  call   0x8049460 <malloc>
   0x080498e8 <+680>:   89 c5   mov    %eax,%ebp

Adding -fno-tree-dse to the compiler flags works around this bug.  efence.i
attached (which is basically a concatenation of efence.h, efence.c, page.c,
print.c, and tstheap.c from the electric-fence 2.1.16 package in Debian).


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2013-10-16 13:14 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-09-08 17:06 [Bug tree-optimization/50337] New: -ftree-dse performs wrong elimination on electric-fence cjwatson at ubuntu dot com
2011-09-08 17:08 ` [Bug tree-optimization/50337] " cjwatson at ubuntu dot com
2011-09-08 17:22 ` cjwatson at ubuntu dot com
2011-09-08 18:10 ` pinskia at gcc dot gnu.org
2011-09-19 15:22 ` cjwatson at ubuntu dot com
2013-10-16 13:14 ` glisse at gcc dot gnu.org

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