I really need help!

I really need help!

[Gavin Li]

I am not sure if I should send this mail to here.

I use gcc (2.95.3) compile a file which include a
function start(), 
the C file is:
/* Hardware boot loader */
void start(void)
{
	asm ("movl %esp, 0x5000");
	for (;;)
	{
        	/* do whatever I want, such as call foo() */
		foo();
	}
}
foo()
{
   ...
}

the command line used to compile :
gcc -O3 -nostdlib -e start -o bootldr.out bootldr.c
objdump -d bootldr.out > bootldr.asm

the ASM output is:
	push %ebp
	mov  %esp, %ebp
	mpv  %esp, 0x5000
	...


My question is how can I get ride of the first two ASM
instructions? I want the compiler to compile my
inlined ASM instruction as the first instruction in
the start() function, and the other function just as
general output.
 
My reason that I want to get ride of those instruction
si:
   I provided -e start to tell compiler that program
should start run from start(). There is no other
function will call this start(), It is the first
function which was run after power on. The first two
ASM instructions are useless. Seriosly, they are
harmful!!!
Because when an embedded system power on, it runs from
start(), the stack pointer is undefined at this time,
it may points to some place where do NOT have memory
at all! so the push instruction will generate
exception! So, I need the compiler to generate start()
which the first instruction is my inline assembler!
    I checked the GCC online manual, but I can't find
how to make gcc works as what I want.
    Anyone who can tell me how to do that?

Thanks a lot,

Gavin

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Re: I really need help!

[Carlo Wood]

Did you try -fomit-frame-pointer ?

On Wed, Oct 17, 2001 at 05:47:49PM -0700, Gavin Li wrote:
> I am not sure if I should send this mail to here.
> 
> I use gcc (2.95.3) compile a file which include a
> function start(), 
> the C file is:
> /* Hardware boot loader */
> void start(void)
> {
> 	asm ("movl %esp, 0x5000");
> 	for (;;)
> 	{
>         	/* do whatever I want, such as call foo() */
> 		foo();
> 	}
> }
> foo()
> {
>    ...
> }
> 
> the command line used to compile :
> gcc -O3 -nostdlib -e start -o bootldr.out bootldr.c
> objdump -d bootldr.out > bootldr.asm
> 
> the ASM output is:
> 	push %ebp
> 	mov  %esp, %ebp
> 	mpv  %esp, 0x5000
> 	...
> 
> 
> My question is how can I get ride of the first two ASM
> instructions? I want the compiler to compile my
> inlined ASM instruction as the first instruction in
> the start() function, and the other function just as
> general output.
>  
> My reason that I want to get ride of those instruction
> si:
>    I provided -e start to tell compiler that program
> should start run from start(). There is no other
> function will call this start(), It is the first
> function which was run after power on. The first two
> ASM instructions are useless. Seriosly, they are
> harmful!!!
> Because when an embedded system power on, it runs from
> start(), the stack pointer is undefined at this time,
> it may points to some place where do NOT have memory
> at all! so the push instruction will generate
> exception! So, I need the compiler to generate start()
> which the first instruction is my inline assembler!
>     I checked the GCC online manual, but I can't find
> how to make gcc works as what I want.
>     Anyone who can tell me how to do that?
> 
> Thanks a lot,
> 
> Gavin
> 
> __________________________________________________
> Do You Yahoo!?
> Make a great connection at Yahoo! Personals.
> http://personals.yahoo.com

-- 
Carlo Wood <carlo@alinoe.com>

Re: I really need help!

[Joern Rennecke]

Carlo Wood wrote:
> 
> Did you try -fomit-frame-pointer ?

That is rather unsafe, since any register saves will still go on the
old stack, and a stack pointer will be used if alloca or friends have
been used.  If the function is kept to just the asm and the function
call, you might as well code it entirely in assembler.

RE: I really need help!

[akbara]

http://webster.cs.ucr.edu/Page_asm/ArtOfAsm.html

l8rz,
-akbara
; vertexabuse.cjb.net


> -----Original Message-----
> From: gcc-owner@gcc.gnu.org [ mailto:gcc-owner@gcc.gnu.org]On Behalf Of
> Gavin Li
> Sent: Wednesday, October 17, 2001 5:48 PM
> To: gcc@gcc.gnu.org
> Subject: I really need help!
> 
> 
> I am not sure if I should send this mail to here.
> 
> I use gcc (2.95.3) compile a file which include a
> function start(), 
> the C file is:
> /* Hardware boot loader */
> void start(void)
> {
> 	asm ("movl %esp, 0x5000");
> 	for (;;)
> 	{
>         	/* do whatever I want, such as call foo() */
> 		foo();
> 	}
> }
> foo()
> {
>    ...
> }
> 
> the command line used to compile :
> gcc -O3 -nostdlib -e start -o bootldr.out bootldr.c
> objdump -d bootldr.out > bootldr.asm
> 
> the ASM output is:
> 	push %ebp
> 	mov  %esp, %ebp
> 	mpv  %esp, 0x5000
> 	...
> 
> 
> My question is how can I get ride of the first two ASM
> instructions? I want the compiler to compile my
> inlined ASM instruction as the first instruction in
> the start() function, and the other function just as
> general output.
>  
> My reason that I want to get ride of those instruction
> si:
>    I provided -e start to tell compiler that program
> should start run from start(). There is no other
> function will call this start(), It is the first
> function which was run after power on. The first two
> ASM instructions are useless. Seriosly, they are
> harmful!!!
> Because when an embedded system power on, it runs from
> start(), the stack pointer is undefined at this time,
> it may points to some place where do NOT have memory
> at all! so the push instruction will generate
> exception! So, I need the compiler to generate start()
> which the first instruction is my inline assembler!
>     I checked the GCC online manual, but I can't find
> how to make gcc works as what I want.
>     Anyone who can tell me how to do that?
> 
> Thanks a lot,
> 
> Gavin
> 
> __________________________________________________
> Do You Yahoo!?
> Make a great connection at Yahoo! Personals.
> http://personals.yahoo.com

Re: I really need help!

[mike stump]

> Date: Wed, 17 Oct 2001 17:47:49 -0700 (PDT)
> From: Gavin Li <gavinux@yahoo.com>
> To: gcc@gcc.gnu.org

> I am not sure if I should send this mail to here.

Kinda _not_ what this list is for.

> void start(void)
> {
> 	asm ("movl %esp, 0x5000");
> }

> My question is how can I get ride of the first two ASM
> instructions?

Go cheat off of newlib, or libc, or glibc, or netbsd, or freebsd...

> I want the compiler to compile my inlined ASM instruction as the
> first instruction in the start() function, and the other function
> just as general output.

Trivial:

void mystart() {
  asm("start:");
  asm("movl %esp, 0x5000");
}

or learn to code in assembler.

Re: I really need help!

[Davide Libenzi]

On Wed, 17 Oct 2001, mike stump wrote:

> > Date: Wed, 17 Oct 2001 17:47:49 -0700 (PDT)
> > From: Gavin Li <gavinux@yahoo.com>
> > To: gcc@gcc.gnu.org
>
> > I am not sure if I should send this mail to here.
>
> Kinda _not_ what this list is for.
>
> > void start(void)
> > {
> > 	asm ("movl %esp, 0x5000");
> > }
>
> > My question is how can I get ride of the first two ASM
> > instructions?
>
> Go cheat off of newlib, or libc, or glibc, or netbsd, or freebsd...
>
> > I want the compiler to compile my inlined ASM instruction as the
> > first instruction in the start() function, and the other function
> > just as general output.
>
> Trivial:
>
> void mystart() {
>   asm("start:");
>   asm("movl %esp, 0x5000");
              ^^^^^^^^^^^^

The function startup code won't be the only one you're going to have with
this instruction, aka gcc swap intel syntax.



- Davide

Re: I really need help!

[Joern Rennecke]

mike stump wrote:
> 
> > Date: Wed, 17 Oct 2001 17:47:49 -0700 (PDT)
> > From: Gavin Li <gavinux@yahoo.com>
> > To: gcc@gcc.gnu.org
> 
> > I am not sure if I should send this mail to here.
> 
> Kinda _not_ what this list is for.
> 
> > void start(void)
> > {
> > 	asm ("movl %esp, 0x5000");
> > }
> 
> > My question is how can I get ride of the first two ASM
> > instructions?
> 
> Go cheat off of newlib, or libc, or glibc, or netbsd, or freebsd...
> 
> > I want the compiler to compile my inlined ASM instruction as the
> > first instruction in the start() function, and the other function
> > just as general output.
> 
> Trivial:
> 
> void mystart() {
>   asm("start:");
>   asm("movl %esp, 0x5000");
> }
> 
> or learn to code in assembler.

Another option would be to implement the naked function attribute for i386,
or making naked [functions] attribute an attribute that has a default
implementation for all targets.

-- 
Joern Rennecke                  |            gcc expert for hire
amylaar@onetel.net.uk           |  send enquiries to: jwr_jobs@onetel.net.uk