Issue in stack.c with AIX xlc compiler with optimization level 2 (-O2) (branch 1.1.1) #10624
Description
I'm building openssl on AIX using xlc and found an issue in the function OPENSSL_sk_dup() in stack.c when compiling with optimization level 2 or higher (-O2).
The issue is that the direct struct assignment gets removed by the compiler (probably a compiler bug)
OPENSSL_STACK *OPENSSL_sk_dup(const OPENSSL_STACK *sk)
{
OPENSSL_STACK *ret;
if ((ret = OPENSSL_malloc(sizeof(*ret))) == NULL) {
CRYPTOerr(CRYPTO_F_OPENSSL_SK_DUP, ERR_R_MALLOC_FAILURE);
return NULL;
}
/* direct structure assignment */
*ret = *sk; /* <---- This line gets removed with -O2 */
if (sk->num == 0) {
/* postpone |ret->data| allocation */
ret->data = NULL;
ret->num_alloc = 0;
return ret;
}
/* duplicate |sk->data| content */
if ((ret->data = OPENSSL_malloc(sizeof(*ret->data) * sk->num_alloc)) == NULL)
goto err;
memcpy(ret->data, sk->data, sizeof(void *) * sk->num);
return ret;
err:
OPENSSL_sk_free(ret);
return NULL;
}
I did some testing and created a simple test program. When the program is compiled on AIX with xlc -O2, the program output will be "Copy failed!!".
The program can be fixed by moving the function wrapper_get_num() below the definition of "struct number" or by replacing the structure assignment by a memcopy or building with -O0.
The function "OPENSSL_sk_dup" in stack.c suffer from the same issue as the function "dup" in this test program.
Is this issue known by openssl and how would you suggest to fix it?
For now I replaced the assignment with memcpy, but there might be better options. Also I don't like to build openssl with custom patches if it can be avoided.
simple test program:
#include <stdlib.h>
#include <stdio.h>
int get_num(struct number * st) ;
int wrapper_get_num(void * st) {
return get_num(st);
}
struct number
{
int num;
};
/* If the function wrapper_get_num(void *st) is moved here, then the issue disappears */
struct number *dup(const struct number *a)
{
struct number *b;
b = malloc(sizeof(*b));
/* Assignment gets removed by xlc compiler with -O2 */
*b = *a;
return b;
}
int get_num(struct number * st){
return st->num;
}
int main (void) {
struct number *a;
struct number *b;
a = malloc(sizeof(*a));
a->num = 1;
b = dup(a);
if (a->num != b->num) {
printf("Copy failed!!\n");
return 1;
}
printf("Copy worked!!\n");
return 0;
}
Compile with:
/usr/vac/bin/xlc_r -qpic -q64 -qmaxmem=16384 -qro -qroconst -qthreaded -O2 -o test.out test.c
xlc version I used:
>/usr/vac/bin/xlc_r -qVersion
IBM XL C/C++ for AIX, V10.1
Version: 10.01.0000.0000