[coreboot] [patch 4/5] libpayload: Add an exec() and i386_do_exec() function

[Uwe Hermann]

On Tue, May 13, 2008 at 05:34:09PM -0600, jordan.crouse at amd.com wrote:
> Add functions for libpayload to execute other payloads in memory,
> and have those functions return cleanly.
> 
> Signed-off-by: Jordan Crouse <jordan.crouse at amd.com>
> Index: libpayload/i386/Makefile.inc
> ===================================================================
> --- libpayload.orig/i386/Makefile.inc	2008-05-13 13:40:07.000000000 -0600
> +++ libpayload/i386/Makefile.inc	2008-05-13 13:42:59.000000000 -0600
> @@ -29,3 +29,4 @@
>  
>  TARGETS-y += i386/head.o i386/main.o i386/sysinfo.o
>  TARGETS-y += i386/timer.o i386/coreboot.o i386/util.o
> +TARGETS-y += i386/exec.o
> Index: libpayload/i386/exec.S
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ libpayload/i386/exec.S	2008-05-13 13:42:59.000000000 -0600
> @@ -0,0 +1,64 @@
> +/* calling syntax:  i386_do_exec(long addr, int argc, char **argv, int *ret) */
> +
> +.align 4
> +.text
> +
> +.global i386_do_exec
> +        .type i386_do_exec, at function
> +
> +i386_do_exec:
> +	pushl %ebp
> +        movl %esp, %ebp
> +	pushl %eax
> +
> +	# Put the run address in %eax
> +	movl 8(%ebp), %eax
> +
> +	# Save off the rest of the registers
> +
> +	pushl %esi
> +	pushl %ecx
> +	pushl %ebp
> +
> +	# Push the argc and argv pointers on to the stack
> +
> +	movl 12(%ebp), %esi
> +	movl 16(%ebp), %ecx
> +
> +	pushl %esi
> +	pushl %ecx
> +
> +	# Move a "magic" number on the stack - the other
> +	# payload will use this as a clue that the argc
> +	# and argv are sane
> +
> +	movl  $12345678, %ecx

This should probably be documented somewhere and/or agreed upon on the list,
as it introduces sort an "API" of some sort? It'll be only relevant for
"our" payloads ("well-behaved" payloads), right?


> +	pushl %ecx
> +
> +	# Jump to the code
> +	call *%eax
> +
> +	/* %eax has the return value */
> +
> +	/* Skip over the argc/argv stuff still on the stack */
> +	addl $12, %esp
> +
> +	# Get back %ebp
> +	popl %ebp
> +
> +	# Get the pointer to the return value
> +	# and save the return value in it
> +
> +	movl 20(%ebp), %ecx
> +	movl %eax, (%eax)
> +
> +	# Get the rest of the saved registers
> +	popl %ecx
> +	popl %esi
> +	popl %eax
> +
> +	# Restore the stack pointer
> +	movl %ebp,%esp
> +	popl %ebp
> +	ret
> +
> Index: libpayload/i386/head.S
> ===================================================================
> --- libpayload.orig/i386/head.S	2008-05-13 13:40:07.000000000 -0600
> +++ libpayload/i386/head.S	2008-05-13 13:42:59.000000000 -0600
> @@ -63,13 +63,14 @@
>  
>  	/* Let's rock. */
>  	call start_main
> -	
> +
> +	/* %eax has the return value - pass it on unmolested */
>  _leave:
>  	/* Get old stack pointer. */
>  	popl %ebx
>  
>  	/* Restore old stack. */
> -	movl %esp, %ebx
> +	movl %ebx, %esp

Is this related, or was it a bug before?

> +#include <libpayload.h>
> +
> +#ifdef CONFIG_TARGET_I386
> +extern void i386_do_exec(long, int, char **, int *);

Please add the argument names, too, if only for consistency.


> +#endif
> +
> +/**
> + * Execute code in memory
> + *
> + * @param ptr The entry point to jump to
> + * @return Return the return value from the entry point
> + */
> +
> +
> +int exec(long addr, int argc, char **argv)
> +{
> +	int val = -1;
> +
> +#ifdef CONFIG_TARGET_I386
> +	i386_do_exec(addr, argc, argv, &val);
> +#endif
> +	return val;
> +}
> Index: libpayload/include/libpayload.h
> ===================================================================
> --- libpayload.orig/include/libpayload.h	2008-05-13 13:42:59.000000000 -0600
> +++ libpayload/include/libpayload.h	2008-05-13 13:42:59.000000000 -0600
> @@ -145,6 +145,9 @@
>  void *calloc(size_t nmemb, size_t size);
>  void *realloc(void *ptr, size_t size);
>  
> +/* libc/exec.c */
> +int exec(long addr, int argc, char **argv);
> +
>  /* libc/lib.c */
>  int bcd2dec(int b);
>  int dec2bcd(int d);
> Index: libpayload/libc/Makefile.inc
> ===================================================================
> --- libpayload.orig/libc/Makefile.inc	2008-05-13 13:40:07.000000000 -0600
> +++ libpayload/libc/Makefile.inc	2008-05-13 13:42:59.000000000 -0600
> @@ -29,4 +29,4 @@
>  
>  TARGETS-y += libc/malloc.o libc/printf.o libc/console.o libc/string.o
>  TARGETS-y += libc/memory.o libc/ctype.o libc/ipchecksum.o libc/lib.o
> -TARGETS-y += libc/rand.o libc/time.o libc/lar.o
> +TARGETS-y += libc/rand.o libc/time.o libc/lar.o libc/exec.o


Uwe.
-- 
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