Frank, thanks for clarification of the calling convention between common
function and system call. /adam
Frank Hofmann wrote:
On Wed, 11 Apr 2007, Adam Zhang wrote:
Hi Oliver,
Yes. the code was running on Linux. Thank you very much for the
correction.
You are right. i just check the AMD64 ABI
(http://www.x86-64.org/documentation.html) that Solaris conforms to.
Because the parameter I need transfer is char array, it needs to be
put in the stack during the calling.
write(2) takes a pointer to that. Where you store the actual array is
up to you.
But do you know where i can find the x86 ABI that Solaris uses?
You might've noticed that neither the AMD64 ABI nor the i386 ABI
anywhere mention the system call mechanism (apart from the _exit
special case in the i386 ABI, where it says you can 'lcall 7, $0'). It
is deliberately undocumented, so that operating systems are free to
choose the fastest method to perform a system call, and/or change that
method, at any time.
If you want to know how a specific UNIX-style OS performs system
calls, you can't look at the ABI document - but you'll have to look at
the sourcecode for the OS' syscall handler and/or the actual binary of
libc.
The calling conventions (it says "function calling sequence") for
library interfaces that are described in the ABI are not the same as
the system call mechanism. This is particularly obvious on Linux
(where the 32bit userland ABI uses the 'normal' stack parameter
passing while the system call mechanism passes args in regs), but also
on Solaris (where you have multiple different ways of performing
system calls).
FrankH.
Regards,
adam
Oliver Yang wrote:
Oliver Yang wrote:
Adam Zhang wrote:
Hi all,
i just write an independent write function in assembly language to
write a string to stderr.
But the code doesn't work on Solaris.
It seems you are using Gcc inline asm which will generate a system
call by issuing "int 0x91".
But you should know, doesn't like Linux, on 32bit x86, Solaris
passes parameters via stack by "push" instead of using registers.
That means, you should besides using %eax as syscall number, you
should push necessary parameters into stack before issuing "int 0x91".
Hi Adam,
Sorry for my poor English. :-[
I have checked your code, I think you inline ASM code are learned
from Linux, not Solaris. In your code, you are trying to pass
parameters by registers before issuing int 0x91:
%eax: 0x4 -> syscall number %ebx: 0x2 --> fd
%ecx buf address
%edx: int size
But actually, on Solaris x86 32bit kernel, except syscall number
should be passed by %eax, other parameters should be passed by
pushing them in stack, please refer to following code:
# /usr/sfw/bin/gcc test.c
# ./a.out
hello
# cat test.c
void write_stderr ( char * buf, int n )
{
int block[2];
block[0] = (int) buf;
block[1] = n;
__asm__ volatile (
"pushl %%ebx\n"
"movl %0, %%ebx\n"
"pushl %%ebx\n"
"movl $4, %%eax\n"
"push 4(%%ebx)\n"
"push 0(%%ebx)\n"
"push $2\n"
"push %%esp\n"
"int $0x91\n"
"addl $3,%%esp\n"
"movl %%eax, 0(%%ebx)\n"
"popl %%ebx\n"
: /*wr*/
: /*rd*/ "g" (block)
: /*trash*/ "eax", "edi", "ecx", "edx", "memory", "cc"
);
}
int main()
{
char s[]="hello\n";
write_stderr(s, sizeof(s) );
return 0;
}
Another thing is, you should run your program on Solaris Nevada,
because you used "int 0x91".
You could use mdb debug your program by setting break point
before int 0x91, check whether you provide right parameters in
stack and %eax.
Below is the code:
void write_stderr ( char * buf, int n )
{
int block[2];
block[0] = (int) buf;
block[1] = n;
__asm__ volatile (
"pushl %%ebx\n" "movl %0, %%ebx\n"
"pushl %%ebx\n" "movl 0(%%ebx), %%ecx\n"
"movl 4(%%ebx), %%edx\n"
"movl $4, %%eax\n" "movl $2, %%ebx\n"
"int $0x91\n" "popl %%ebx\n" "movl
%%eax, 0(%%ebx)\n"
"popl %%ebx\n" : /*wr*/
: /*rd*/ "g" (block)
: /*trash*/ "eax", "edi", "ecx", "edx", "memory", "cc"
);
}
Does anyone know where i am wrong?
Thank you!
Regards,
adam
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