Hello,
I think I have found a bug in G++ . Please submit it to the bug tracker
(I do not want to open an account there) if you think it is a bug - I am
not sure about it.
While I worked with "search+replace" I accidently had following in my
source code:
const char* DUMMY = DUMMY;
It is amaazing that this code actually does compile. And no warning is
output at all.
The usage of this mysterious constant "DUMMY" causes odd behavior, e.g.
if it is written to a stream, the stream becomes "broken" and nothing
can be written to it anymore:
cout << "Hello world" << endl;
cout << DUMMY;
cout << "You cannot read this. I am broken..." << endl;
I also had in mind that the program might have been crashed/terminated,
but in fact, it is still running. I verified it with a printf() at the
end and it showed me that the program is still running and just the
'cout' stream is gone.
Here are some small reproduceable codes:
1. broken.c:
============
#include <stdio.h>
#include <iostream>
int main(void) {
const char* DUMMY = DUMMY;
std::cout << DUMMY;
return 0;
}
working.c:
============
#include <stdio.h>
#include <iostream>
int main(void) {
const char* DUMMY = "x";
std::cout << DUMMY;
return 0;
}
The diff result of broken.asm and working.asm is:
=====================================================
--- broken.asm 2012-04-29 08:41:25.000000000 +0200
+++ working.asm 2012-04-29 08:41:26.000000000 +0200
@@ -1 +1 @@
- .file "broken.c"
+ .file "working.c"
@@ -3,0 +4,3 @@
+ .section .rodata
+.LC0:
+ .string "x"
@@ -16,0 +20 @@
+ movq $.LC0, -8(%rbp)
A part of working.asm:
======================
.LC0:
.string "x"
.text
main:
.LFB957:
.cfi_startproc
.cfi_personality 0x3,__gxx_personality_v0
pushq %rbp
.cfi_def_cfa_offset 16
movq %rsp, %rbp
.cfi_offset 6, -16
.cfi_def_cfa_register 6
subq $16, %rsp
movq $.LC0, -8(%rbp) // <----- this is missing at
broken.asm!
movq -8(%rbp), %rax
movq %rax, %rsi
movl $_ZSt4cout, %edi
call _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
movl $0, %eax
leave
ret
.cfi_endproc
A part of broken.asm:
======================
main:
.LFB957:
.cfi_startproc
.cfi_personality 0x3,__gxx_personality_v0
pushq %rbp
.cfi_def_cfa_offset 16
movq %rsp, %rbp
.cfi_offset 6, -16
.cfi_def_cfa_register 6
subq $16, %rsp
movq -8(%rbp), %rax
movq %rax, %rsi
movl $_ZSt4cout, %edi
call _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
movl $0, %eax
leave
ret
.cfi_endproc
My 'g++ -v' output:
====================
Es werden eingebaute Spezifikationen verwendet.
Ziel: x86_64-linux-gnu
Konfiguriert mit: ../src/configure -v --with-pkgversion='Debian
4.4.5-8' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.4 --enable-shared --enable-multiarch
--enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib
--enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc --with-arch-32=i586 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread-Modell: posix
gcc-Version 4.4.5 (Debian 4.4.5-8)
(Note: It is the latest version I can get. Since it is a production
system I cannot install newer unstable versions and I do not have a
Linux box at home.)
Best regards
Daniel Marschall
