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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <console.h>
#include <com32.h>
#include <syslinux/loadfile.h>
#define COM32_LOAD_ADDR ((void*)0x101000)
#define STACK_RED_ZONE 0x1000
static inline void error(const char *msg)
{
fputs(msg, stderr);
}
static void shift_cmdline(struct com32_sys_args *com32)
{
char *p;
/* Skip leading whitespace */
for (p = com32->cs_cmdline; *p != '\0' && *p == ' '; p++)
;
/* Skip first word */
for (; *p != '\0' && *p != ' '; p++)
;
/* Skip whitespace after first word */
for (; *p != '\0' && *p == ' '; p++)
;
com32->cs_cmdline = p;
}
static __noreturn reloc_entry(void *ptr, size_t len, uintptr_t entry_esp, uintptr_t module_esp)
{
size_t stack_frame_size = sizeof(struct com32_sys_args) + 4;
struct com32_sys_args *com32;
/* Copy module to load address */
memcpy(COM32_LOAD_ADDR, ptr, len);
/* Copy stack frame onto module stack */
module_esp = (module_esp - stack_frame_size) & ~15;
memcpy((void*)module_esp, (void*)entry_esp, stack_frame_size);
/* Fix up command line */
com32 = (struct com32_sys_args*)((char*)module_esp + 4);
shift_cmdline(com32);
/* Invoke module with stack set up */
asm volatile (
"movl %0, %%esp\n\t"
"jmp *%%ecx"
: : "r"(module_esp), "c"(COM32_LOAD_ADDR)
);
for(;;); /* shut the compiler up */
}
static inline __noreturn reloc(void *ptr, size_t len)
{
extern uintptr_t __entry_esp;
extern char _start[], _end[];
size_t total_size = _end - _start;
__noreturn (*success_fn)(void*, size_t, uintptr_t, uintptr_t);
uint32_t esp;
char *dest;
/* Calculate relocation address, preserve current stack */
asm volatile ("movl %%esp, %0\n\t" : "=m"(esp));
dest = (char*)((esp - STACK_RED_ZONE - total_size) & ~3);
/* Calculate entry point in relocated code */
success_fn = (void*)(dest + ((char*)reloc_entry - _start));
/* Copy all sections to relocation address */
printf("Relocating %d bytes from %p to %p\n", total_size, _start, dest);
memcpy(dest, _start, total_size);
success_fn(ptr, len, __entry_esp, (uintptr_t)dest);
}
int main(int argc, char *argv[])
{
void *data;
size_t data_len;
openconsole(&dev_null_r, &dev_stdcon_w);
if (argc < 2) {
error("Usage: gdbstub.c32 com32_file arguments...\n");
return 1;
}
if (loadfile(argv[1], &data, &data_len)) {
error("Unable to load file\n");
return 1;
}
/* No more lib calls after this point */
reloc(data, data_len);
}
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