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Add memory fences around self-relocating code

This commit is contained in:
flysand7 2023-08-04 06:24:19 +11:00
parent 246e9f2071
commit 48a3a48ce8
1 changed files with 8 additions and 1 deletions
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9
src/loader/loader-self-reloc.c
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@ -21,6 +21,8 @@
#define AUX_CNT 32 #define AUX_CNT 32
#define DYN_CNT 37 #define DYN_CNT 37
#define _mfence() asm volatile("" ::: "memory")
static void print_string_n(char *str, u64 len) { static void print_string_n(char *str, u64 len) {
sys_write(STDOUT_FILENO, str, len); sys_write(STDOUT_FILENO, str, len);
} }
@ -116,7 +118,7 @@ static void printf(char *fmt, ...) {
va_end(args); va_end(args);
} }
#if defined(_DEBUG) || 1 #if defined(_DEBUG)
#define _dbg_print_char(c) print_char(c) #define _dbg_print_char(c) print_char(c)
#define _dbg_print_string(s) print_string(s) #define _dbg_print_string(s) print_string(s)
#define _dbg_print_string_n(s,n) print_string_n(s,n) #define _dbg_print_string_n(s,n) print_string_n(s,n)
@ -203,6 +205,10 @@ void _dlstart_reloc_c(u64 *sp, Elf64_Dyn *dynv) {
if(symtab == NULL) { if(symtab == NULL) {
_dbg_printf("ERROR: No .dynsym found\n"); _dbg_printf("ERROR: No .dynsym found\n");
} }
// Use memory fences, to MAKE SURE the compiler won't reorder code and
// accidentally use relocations when they are not ready. The code before
// this point is carefully written to avoid generating relocations.
_mfence();
// Apply relocations // Apply relocations
if(dyn[DT_REL] != 0) { if(dyn[DT_REL] != 0) {
_dbg_printf("REL Relocations found. This part isn't implemented\n"); _dbg_printf("REL Relocations found. This part isn't implemented\n");
@ -280,6 +286,7 @@ void _dlstart_reloc_c(u64 *sp, Elf64_Dyn *dynv) {
} }
} }
_mfence();
_dbg_printf("Self-relocation finished. Entering the loader\n"); _dbg_printf("Self-relocation finished. Entering the loader\n");
loader_entry(sp, dyn, aux); loader_entry(sp, dyn, aux);
sys_exit(0); sys_exit(0);