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Strengthen against possible compiler optimizations

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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2023-11-09 21:46:24 +01:00
parent 2c04f57ffc
commit 53833516bf
1 changed files with 11 additions and 7 deletions
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18
programs/test/metatest.c
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@ -25,10 +25,15 @@
/* This is an external variable, so the compiler doesn't know that we're never /* This is an external variable, so the compiler doesn't know that we're never
* changing its value. * changing its value.
*
* TODO: LTO (link-time-optimization) would defeat this.
*/ */
int false_but_the_compiler_does_not_know = 0; volatile int false_but_the_compiler_does_not_know = 0;
/* Set n bytes at the address p to all-bits-zero, in such a way that
* the compiler should not know that p is all-bits-zero. */
static void set_to_zero_but_the_compiler_does_not_know(void *p, size_t n)
{
memset(p, false_but_the_compiler_does_not_know, n);
}
/****************************************************************/ /****************************************************************/
@ -50,7 +55,7 @@ void null_pointer_dereference(const char *name)
{ {
(void) name; (void) name;
volatile char *p; volatile char *p;
mbedtls_platform_zeroize((void *) &p, sizeof(p)); set_to_zero_but_the_compiler_does_not_know(&p, sizeof(p));
mbedtls_printf("%p -> %u\n", p, (unsigned) *p); mbedtls_printf("%p -> %u\n", p, (unsigned) *p);
} }
@ -58,7 +63,7 @@ void null_pointer_call(const char *name)
{ {
(void) name; (void) name;
unsigned (*p)(void); unsigned (*p)(void);
mbedtls_platform_zeroize(&p, sizeof(p)); set_to_zero_but_the_compiler_does_not_know(&p, sizeof(p));
/* The pointer representation may be truncated, but we don't care: /* The pointer representation may be truncated, but we don't care:
* the only point of printing it is to have some use of the pointer * the only point of printing it is to have some use of the pointer
* to dissuade the compiler from optimizing it away. */ * to dissuade the compiler from optimizing it away. */
@ -104,8 +109,7 @@ void memory_leak(const char *name)
{ {
(void) name; (void) name;
volatile char *p = mbedtls_calloc(1, 1); volatile char *p = mbedtls_calloc(1, 1);
/* Hint to the compiler that calloc must not be optimized away. */ mbedtls_printf("%u\n", (unsigned) *p);
(void) *p;
} }