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我再附上一点资料，grub4dos的readme中的。
******************************************************************************
*** Running User Programs ***
******************************************************************************
From 0.4.5 on, user programs can be developed for running under grub4dos. The
executable program file must end with the 8-byte grub4dos EXEC signature:
0x05, 0x18, 0x05, 0x03, 0xBA, 0xA7, 0xBA, 0xBC
The executable must have no relocations, and the entry point is at the very
beginning of the file, just like a DOS .com file(but the grub4dos executable
is 32-bit).
Here is a sample file echo.c:
/*================ begin echo.c ================*/
/*
* compile:
gcc -nostdlib -fno-zero-initialized-in-bss -fno-function-cse -fno-jump-tables -Wl,-N -fPIE echo.c
* disassemble: objdump -d a.out
* confirm no relocation: readelf -r a.out
* generate executable: objcopy -O binary a.out b.out
*
* and then the resultant b.out will be grub4dos executable.
*/
/*
* This is a simple ECHO command, running under grub4dos.
*/
int i = 0x66666666; /* this is needed, see the following comment. */
/* gcc treat the following as data only if a global initialization like the
* above line occurs.
*/
/* a valid executable file for grub4dos must end with these 8 bytes */
asm(".long 0x03051805");
asm(".long 0xBCBAA7BA");
/* thank goodness gcc will place the above 8 bytes at the end of the b.out
* file. Do not insert any other asm lines here.
*/
int
main()
{
void *p = &main;
return
/* the following line is calling the grub_sprintf function. */
((int (*)(char *, const char *, ...))((*(int **)0x8300)[0]))
/* the following line includes arguments passed to grub_sprintf. */
(0, p - (*(int *)(p - 8)));
}
/*================ end echo.c ================*/
0x8300 is a pointer to the grub4dos system funtions(API). The system_functions
variable is defined in asm.S. |
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IP卡
狗仔卡
发表于 2009-10-3 00:35:46
显身卡
