Sent from my iPhone
On Oct 6, 2008, at 5:09 AM, Denis <[EMAIL PROTECTED]> wrote:
Hi,
I use gcc:
[EMAIL PROTECTED] ~]$ gcc -v
Using built-in specs.
Target: x86_64-suse-linux
Configured with: ../configure --enable-threads=posix --prefix=/usr --
with-local-prefix=/usr/local --infodir=/usr/share/info --mandir=/usr/
share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64 --enable-
languages=c,c++,objc,fortran,java,ada --enable-checking=release --
with-gxx-include-dir=/usr/include/c++/4.1.0 --enable-ssp --disable-
libssp --enable-java-awt=gtk --enable-gtk-cairo --disable-libjava-
multilib --with-slibdir=/lib64 --with-system-zlib --enable-shared --
enable-__cxa_atexit --enable-libstdcxx-allocator=new --without-
system-libunwind --with-cpu=generic --host=x86_64-suse-linux
Thread model: posix
gcc version 4.1.0 (SUSE Linux)
and trying to compile program:
################################
void plus (long * a, long * b)
{
long aa = 10;
long bb =10;
*a += *b + aa + bb;
}
int main (){
long a = 1;
long b = 2;
long *aa = &a;
long *bb = &b;
plus(aa,bb);
}
######################################
[EMAIL PROTECTED] gc]$ gcc -S main.c
But code produced for plus function is incorrect:
.file "main.c"
.text
.globl plus
.type plus, @function
plus:
.LFB2:
pushq %rbp
.LCFI0:
movq %rsp, %rbp
.LCFI1:
##################>>>>>>> As you can see here it allocates
parameters and autos into stack minus shifts, that is free stack
space. I.e. it didn.t reservation.
This is ok as the x86_64 ABI has a red zone. If you are running into a
problem, then your kernel is not following the ABI.
movq %rdi, -24(%rbp)
movq %rsi, -32(%rbp)
movq $10, -16(%rbp)
movq $10, -8(%rbp)
movq -24(%rbp), %rax
movq (%rax), %rdx
movq -32(%rbp), %rax
movq (%rax), %rax
addq -16(%rbp), %rax
addq -8(%rbp), %rax
addq %rax, %rdx
movq -24(%rbp), %rax
movq %rdx, (%rax)
leave
ret
.LFE2:
.size plus, .-plus
.globl main
.type main, @function
main:
.LFB3:
pushq %rbp
.LCFI2:
movq %rsp, %rbp
.LCFI3:
#################>>>>>>>>>> Here it does all correct . firstly
reserve stack frame and then allocates autos and parameters there.
subq $32, %rsp
.LCFI4:
movq $1, -24(%rbp)
movq $2, -32(%rbp)
leaq -24(%rbp), %rax
movq %rax, -16(%rbp)
leaq -32(%rbp), %rax
movq %rax, -8(%rbp)
movq -8(%rbp), %rsi
movq -16(%rbp), %rdi
call plus
leave
ret:
The difference between functions is that main calls other function
and .plus. does not.
In my project I have kernel code that has a function w/o calls
(memcpy) and it is compiled also incorrectly.
And problem is that when *dst = *src executed . pagefault appeared,
this pagefault works on the same stack and rewrites free space, i.e.
rewrites locals of memcpy function.
That results to crash on next read from src.
So probably somebody knows how to solve this problem? I.ve explored
gcc flags and didn.t find anything to solve it.
I.ve also tried another gcc version :
[EMAIL PROTECTED] gc]$ gcc -v
Reading specs from /usr/lib/gcc/x86_64-redhat-linux/3.4.5/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix --
disable-checking --with-system-zlib --enable-__cxa_atexit --disable-
libunwind-exceptions --enable-java-awt=gtk --host=x86_64-redhat-linux
Thread model: posix
gcc version 3.4.5 20051201 (Red Hat 3.4.5-2)
Result is the same.
Thank you in advance,
Denis.
