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#include <shared/printf.h>
#include <user/lib/elf.h>
#include <user/lib/syscall.c>
const char *str = "Hello!\n", *str2 = "World.\n";
__attribute__((visibility("hidden")))
extern struct Elf64_Dyn _DYNAMIC[];
__attribute__((visibility("hidden")))
extern char _image_base;
static void printf_backend(void *arg, const char *buf, size_t len) {
(void)arg;
_syscall_write(1, buf, len, -1);
}
int printf(const char *fmt, ...) {
int ret = 0;
va_list argp;
va_start(argp, fmt);
ret = __printf_internal(fmt, argp, printf_backend, 0);
va_end(argp);
return ret;
}
static struct Elf64_Dyn *dyn_gettag(Elf64_Xword tag) {
for (size_t i = 0;; i++) {
if (_DYNAMIC[i].d_tag == tag) return &_DYNAMIC[i];
if (_DYNAMIC[i].d_tag == DT_NULL) return NULL;
}
}
static void reloc(void) {
// TODO DT_REL
if (dyn_gettag(DT_PLTGOT) || dyn_gettag(DT_JMPREL)) {
printf("elf: unimplemented tag in _DYNAMIC\n");
}
struct Elf64_Dyn *rela_tag = dyn_gettag(DT_RELA);
if (rela_tag) {
/* not checking pointer validity,
* crashing on an invalid elf is fine */
size_t relasz = dyn_gettag(DT_RELASZ)->d_val;
size_t relaent = dyn_gettag(DT_RELAENT)->d_val;
for (size_t o = 0; o < relasz; o += relaent) {
struct Elf64_Rela *r = &_image_base + rela_tag->d_ptr + o;
uintptr_t *target = &_image_base + r->r_offset;
switch (ELF64_R_TYPE(r->r_info)) {
case R_X86_64_RELATIVE:
*target = &_image_base + r->r_addend;
break;
default:
printf("elf: unsupported relocation type\n");
}
}
}
}
int main(void) {
printf("loaded at %x\n", &_image_base);
reloc();
printf(str);
printf(str2);
_syscall_exit(0);
}
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