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Add assertions for dangerous bit shift that could trigger undefined

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behaviour

Change-Id: I051ed229d407eafcae1ea4b5fc745176a751e036
This commit is contained in:
Émilie Feral
2017-11-30 13:55:11 +01:00
parent da2829b969
commit 3f0328f5b5
5 changed files with 31 additions and 2 deletions
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7
liba/src/aeabi-rt/llsl.c
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@@ -1,10 +1,17 @@
/* See the "Run-time ABI for the ARM Architecture", Section 4.2 */
#include <assert.h>
typedef unsigned int uint32_t;
long long __aeabi_llsl(long long value, int shift) {
uint32_t low = (uint32_t)value << shift;
/* "Shift behavior is undefined if the right operand is negative, or greater
* than or equal to the length in bits of the promoted left operand" according
* to C++ spec. However, arm compiler fill the vacated bits with 0 */
assert(shift < 32 || low == 0);
uint32_t high = ((uint32_t)(value >> 32) << shift);
// Same comment
assert(shift < 32 || high == 0);
if (shift < 32) {
high |= ((uint32_t)value >> (32 - shift));
} else {

7
liba/src/aeabi-rt/llsr.c
View File

@@ -1,14 +1,21 @@
/* See the "Run-time ABI for the ARM Architecture", Section 4.2 */
#include <assert.h>
typedef unsigned int uint32_t;
long long __aeabi_llsr(long long value, int shift) {
uint32_t low = ((uint32_t)value >> shift);
/* "Shift behavior is undefined if the right operand is negative, or greater
* than or equal to the length in bits of the promoted left operand" according
* to C++ spec. However, arm compiler fill the vacated bits with 0 */
assert(shift < 32 || low == 0);
if (shift < 32) {
low |= ((uint32_t)(value >> 32) << (32 - shift));
} else {
low |= ((uint32_t)(value >> 32) >> (shift - 32));
}
uint32_t high = (uint32_t)(value >> 32) >> shift;
// Same comment
assert(shift < 32 || high == 0);
return ((long long)high << 32) | low;
}