I have a templated function which uses inline assembler (with MMX
instructions). Inline assembler is passed pointer to array element.
When this function is instantiated for the first time, code before inline
assembler is generated correctly. When it is instantiated for the second time,
one of registers used in inline assembler is not loaded from stack and causes
segfault when it is dereferenced in inline assembler.
I will attach test case.
g4.0 -v:
Using built-in specs.
Target: i486-linux-gnu
Configured with: /src/configure -v
,c++,java,f95,objc,ada,treelang /usr
/usr/lib
/
i486-linux-gnu
Thread model: posix
gcc version 4.0.2 (Debian 4.0.2-2)

Comment #1 from krzysiek-gcc dot gnu dot org at lichota dot net 2005-11-09 19:46
Created an attachment (id=10193)
()
Testcase for the bug

This is the testcase. Compile with:
g4.0 -save-temps -fPIC -ggdb3 -Wno-non-virtual-dtor -pthread
-fkeep-inline-functions testcase10.cpp

When both calls to bar() are instantiated, the segfault occurs.
When only one is instantiated (the other is commented out), it works correctly.

Comment #2 from krzysiek-gcc dot gnu dot org at lichota dot net 2005-11-09 19:49
Created an attachment (id=10195)
()
Assembler code generated from testcase

This is code generated from testcase.
In first instantiation eax register is loaded before inline asm starts:
.loc 1 25 0
movl -16(%ebp), %eax
addl -20(%ebp), %eax
sall $2, %eax
addl 8(%ebp), %eax
movl %eax, -8(%ebp)
.loc 1 41 0
movl -16(%ebp), %eax
addl -24(%ebp), %eax
sall $2, %eax
movl %eax, %edx
addl -12(%ebp), %edx
movl -8(%ebp), %eax
#APP
movq (%edx), %mm0 ;

In the second instantiation, eax is not loaded:
.loc 1 25 0
movl -16(%ebp), %eax
addl -20(%ebp), %eax
sall $2, %eax
addl 8(%ebp), %eax
movl %eax, -8(%ebp)
.loc 1 41 0
movl -16(%ebp), %eax
addl -24(%ebp), %eax
sall $2, %eax
movl %eax, %edx
addl -12(%ebp), %edx
#APP
movq (%edx), %mm0 ;

Then in line:
pxor (%eax), %mm0 ;

eax is dereferenced and segfault occurs.

Comment #3 from krzysiek-gcc dot gnu dot org at lichota dot net 2005-11-09 20:00
Created an attachment (id=10196)
()
Correct code generated by g++ 3.4.2
This is the correct code generated by g++ 3.4.2. It loads eax before inline asm
starts in both instantiations.

Comment #4 from pinskia at gcc dot gnu dot org 2005-11-09 20:24
Simplified example:
template <int>
int f(int i)
{
asm("%0 %1 " : "+r"(i) );
return i;
}
int main(void)
{
f<0>(0)+ f<1>(0);
}

Comment #5 from pinskia at gcc dot gnu dot org 2005-11-09 20:28
For the first time template is instantiated, we get:
__asm__("%0 %1 ":"=r" i:"0" i);
The second time, we get:
__asm__("%0 %1 ":"=r" i:);
Somehow we brought back a bug from 2.95.3 (weird isn't it).

Comment #6 from jakub at gcc dot gnu dot org 2005-11-12 20:42
Subject: Bug 24761

Author: jakub
Date: Sat Nov 12 20:42:23 2005
New Revision: 106831

URL:
Log:
PR c++/24761
* pt.c (tsubst_copy_asm_operands): New function.
(tsubst_expr) <case ASM_EXPR>: Use it.

* gdg/template/asm1.C: New test.

Added:

Modified:
trunk/gcc/cp/ChangeLog
trunk/gcc/cp/pt.c
trunk/gcc/testsuite/ChangeLog

Comment #7 from jakub at gcc dot gnu dot org 2005-11-12 20:43
Subject: Bug 24761

Author: jakub
Date: Sat Nov 12 20:43:27 2005
New Revision: 106832

URL:
Log:
PR c++/24761
* pt.c (tsubst_copy_asm_operands): New function.
(tsubst_expr) <case ASM_EXPR>: Use it.

* gdg/template/asm1.C: New test.

Added:

Modified:

Comment #8 from pinskia at gcc dot gnu dot org 2005-11-12 22:13
Fixed.