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string-util: rework memory_erase() to not use GCC optimize attribute (#…


"#pragma GCC optimize" is merely a convenience to decorate multiple
functions with attribute optimize. And the manual has this to say about
this attribute:

  This attribute should be used for debugging purposes only. It
  is not suitable in production code.

Some versions of GCC also seem to have a problem with this pragma in
combination with LTO, resulting in ICEs.

So use a different approach (indirect the memset call via a volatile
function pointer) as implemented in openssl's crypto/mem_clr.c.

Closes: #3811
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mbiebl authored and keszybz committed Jul 27, 2016
1 parent 5a8ff0e commit b6b609dbc202e5645fc58e87b8a7d46426ee4bb7
Showing with 11 additions and 15 deletions.
  1. +11 −15 src/basic/string-util.c
@@ -22,6 +22,7 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
+#include <string.h>
#include "alloc-util.h"
#include "gunicode.h"
@@ -822,25 +823,20 @@ int free_and_strdup(char **p, const char *s) {
return 1;
-#pragma GCC push_options
-#pragma GCC optimize("O0")
+ * Pointer to memset is volatile so that compiler must de-reference
+ * the pointer and can't assume that it points to any function in
+ * particular (such as memset, which it then might further "optimize")
+ * This approach is inspired by openssl's crypto/mem_clr.c.
+ */
+typedef void *(*memset_t)(void *,int,size_t);
-void* memory_erase(void *p, size_t l) {
- volatile uint8_t* x = (volatile uint8_t*) p;
- /* This basically does what memset() does, but hopefully isn't
- * optimized away by the compiler. One of those days, when
- * glibc learns memset_s() we should replace this call by
- * memset_s(), but until then this has to do. */
- for (; l > 0; l--)
- *(x++) = 'x';
+static volatile memset_t memset_func = memset;
- return p;
+void* memory_erase(void *p, size_t l) {
+ return memset_func(p, 'x', l);
-#pragma GCC pop_options
char* string_erase(char *x) {
if (!x)

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