Re: one simple question
> > > I compile a test C file. I notice there are a few lines at the > > > beginning of the assembly code. I want to know what it means, but > > > can't figure out one of them. Can anyone tell me what the > > > following line does please? > > > > > > and$0xfff0,%esp > > > > gcc2_compiled.: > > .text > > .p2align 2,0x90 > > .globl main > > .typemain,@function > > main: > > pushl %ebp > > movl %esp,%ebp > > xorl %eax,%eax > > jmp .L2 > > .p2align 2,0x90 > > .L2: > > thank you very much for the reply > yes and I am using gcc 3.2.2 > if you "gdb" the executable and "disassemble main" > you will see the line like that > but if you use gcc -S something.s something.c > it won't appear in the assembly code Ah, so it's being introduced by the assembler, not the compiler. That is perhaps the effect of alignement instructions like > > .text > > .p2align 2,0x90 this and similar defaults. > and I google around, I think it does the alignment for optimization > purpose, in that case the memory access will be faster according to the > article. That may very well be the case. Considering that a cache line is also a few words worth, it may be sensible to start with an aligned stack frame too. > best regards, > Chungwei -- Cordula's Web. http://www.cordula.ws/ ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: one simple question
thank you very much for the reply
yes and I am using gcc 3.2.2
if you "gdb" the executable and "disassemble main"
you will see the line like that
but if you use gcc -S something.s something.c
it won't appear in the assembly code
and I google around, I think it does the alignment for optimization
purpose, in that case the memory access will be faster according to the
article.
best regards,
Chungwei
--- Cordula's Web <[EMAIL PROTECTED]> wrote:
> > I compile a test C file. I notice there are a few lines at the
> > beginning of the assembly code. I want to know what it means, but
> > can't figure out one of them. Can anyone tell me what the
> > following line does please?
> >
> > and$0xfff0,%esp
>
> Hmmm, when I compile the simplest possible C file:
>
> ---
> int
> main (int argc, char *argv[])
> {
> return 0;
> }
>
>
> I get this:
>
>
> .file "test1.c"
> .version"01.01"
> gcc2_compiled.:
> .text
> .p2align 2,0x90
> .globl main
> .typemain,@function
> main:
> pushl %ebp
> movl %esp,%ebp
> xorl %eax,%eax
> jmp .L2
> .p2align 2,0x90
> .L2:
> leave
> ret
> .Lfe1:
> .sizemain,.Lfe1-main
> .ident "GCC: (GNU) c 2.95.4 20020320 [FreeBSD]"
>
>
>
> No such thing as:
>
> and$0xfff0,%esp
>
> Are you using gcc 3.3.x?
>
> Anyway, this code looks like it would align the stack
> the stack pointer...
>
> > best regards
> > Chungwei
>
> --
> Cordula's Web. http://www.cordula.ws/
>
=
bear
___
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Re: one simple question
> I compile a test C file. I notice there are a few lines at the
> beginning of the assembly code. I want to know what it means, but
> can't figure out one of them. Can anyone tell me what the
> following line does please?
>
> and$0xfff0,%esp
Hmmm, when I compile the simplest possible C file:
---
int
main (int argc, char *argv[])
{
return 0;
}
I get this:
.file "test1.c"
.version"01.01"
gcc2_compiled.:
.text
.p2align 2,0x90
.globl main
.typemain,@function
main:
pushl %ebp
movl %esp,%ebp
xorl %eax,%eax
jmp .L2
.p2align 2,0x90
.L2:
leave
ret
.Lfe1:
.sizemain,.Lfe1-main
.ident "GCC: (GNU) c 2.95.4 20020320 [FreeBSD]"
No such thing as:
and$0xfff0,%esp
Are you using gcc 3.3.x?
Anyway, this code looks like it would align the stack
the stack pointer...
> best regards
> Chungwei
--
Cordula's Web. http://www.cordula.ws/
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Re: one simple question
On Wed, 3 Mar 2004 18:13:43 + chungwei Hsiung <[EMAIL PROTECTED]> wrote: > Hello.. > I have a simple question, but I am not sure what the answer is. If > anyone can possibly help me, it is really appreciated. I compile a > test C file. I notice there are a few lines at the beginning of the > assembly code. I want to know what it means, but can't figure out > one of them. Can anyone tell me what the following line does please? > > and$0xfff0,%esp > > best regards > Chungwei Hi Chungwei, I believe that instruction is used to align the stack pointer to a 16-byte boundary, for efficiency. However, this is just a guess, based on some discussions I've seen. I don't know for certain. You may have better luck asking on [EMAIL PROTECTED] -Chris ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
one simple question
Hello.. I have a simple question, but I am not sure what the answer is. If anyone can possibly help me, it is really appreciated. I compile a test C file. I notice there are a few lines at the beginning of the assembly code. I want to know what it means, but can't figure out one of them. Can anyone tell me what the following line does please? and$0xfff0,%esp best regards Chungwei ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
