[Bug c++/66603] New: using std::cout causes segfault with unrelated array declaration

[Bug c++/66603] New: using std::cout causes segfault with unrelated array declaration

[gunney1 at llnl dot gov]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66603

            Bug ID: 66603
           Summary: using std::cout causes segfault with unrelated array
                    declaration
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gunney1 at llnl dot gov
  Target Milestone: ---

Created attachment 35816
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35816&action=edit
.ii file from g++ command

Replicator:

#include <iostream>
int main () {
   std::cout << 1;
   int a[4000000];
   // int *a = new int[8000000]; delete [] a;
}

this program segfaults with g++ (4.5.0, 4.6.1, 4.8.4, 5.1.0) but not with icpc.
Oddly, commenting out the stream insert fixes the segfault.
Replacing array with new/delete also works.
New/delete allocates more data, so memory is not the issue here.

> g++ -v -save-temps P1.C
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-5.1.0/configure
--prefix=/home/gunney1/opt/gcc/5.1.0/installed
Thread model: posix
gcc version 5.1.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'

/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/cc1plus
-E -quiet -v -D_GNU_SOURCE P1.C -mtune=generic -march=x86-64 -fpch-preprocess
-o P1.ii
ignoring nonexistent directory
"/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../x86_64-unknown-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:

/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../include/c++/5.1.0

/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../include/c++/5.1.0/x86_64-unknown-linux-gnu

/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../include/c++/5.1.0/backward

/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/include
 /usr/local/include
 /home/gunney1/opt/gcc/5.1.0/installed/include

/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'

/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/cc1plus
-fpreprocessed P1.ii -quiet -dumpbase P1.C -mtune=generic -march=x86-64
-auxbase P1 -version -o P1.s
GNU C++ (GCC) version 5.1.0 (x86_64-unknown-linux-gnu)
        compiled by GNU C version 5.1.0, GMP version 4.3.1, MPFR version 2.4.1,
MPC version 0.8
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (GCC) version 5.1.0 (x86_64-unknown-linux-gnu)
        compiled by GNU C version 5.1.0, GMP version 4.3.1, MPFR version 2.4.1,
MPC version 0.8
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: a812ed01a29b2a8404e588f77961fe34
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 as -v --64 -o P1.o P1.s
GNU assembler version 2.20.51.0.2 (x86_64-redhat-linux) using BFD version
version 2.20.51.0.2-5.42.el6 20100205
COMPILER_PATH=/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/:/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/:/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/:/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/:/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/
LIBRARY_PATH=/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/:/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'

/home/gunney1/opt/gcc/5.1.0/installed/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/collect2
--eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2
/usr/lib/../lib64/crt1.o /usr/lib/../lib64/crti.o
/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/crtbegin.o
-L/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0
-L/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../..
P1.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/home/gunney1/opt/gcc/5.1.0/installed/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/crtend.o
/usr/lib/../lib64/crtn.o
191051 gunney1-lx~/bugrep/gcc-cout-segfault> ./a.out
Segmentation fault (core dumped)

[Bug c++/66603] using std::cout causes segfault with unrelated array declaration

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66603

Marc Glisse <glisse at gcc dot gnu.org> changed:

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

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
That looks like a good old stack overflow, why do you think there is a bug?

[Bug c++/66603] using std::cout causes segfault with unrelated array declaration

[gunney1 at llnl dot gov]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66603

--- Comment #3 from gunney1 at llnl dot gov ---
Because of the effects of the stream insertion.  But maybe I don't understand
very well their relationship.

[Bug c++/66603] using std::cout causes segfault with unrelated array declaration

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66603

--- Comment #4 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to gunney1 from comment #3)
> Because of the effects of the stream insertion.  But maybe I don't
> understand very well their relationship.

First, I guess it does not crash with icpc because icpc optimizes by default.
g++ -O also optimizes 'a' away.

Simply mentioning a huge stack array does not produce the crash. The issue is
when something (anything, in this case placing the arguments for the function
call) tries to use the stack after that array (outside of the stack, since the
array is so large).

[Bug c++/66603] using std::cout causes segfault with unrelated array declaration

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66603

--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> ---
Another detail that might confuse you: if you write
in n=4000000;
int a[n];

it will probably not crash. The reason is that variables like 'int a[4000000]'
exist for the whole length of the function, the memory for them is reserved at
function entry, so the stream operation happens after the memory was reserved.
On the other hand, a dynamic allocation (VLA) happens at the point where it is
requested, i.e. after the stream op, and there is no operation afterwards to
use the stack and crash the program.