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Minor tweaks to recent UBSan-related fix

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* src/alloc.c: No need to include stdalign.h; it’s pervasive.
(GC_STRING_OVERRUN_COOKIE_SIZE): Align to sdata’s alignment,
so that the code works even if alignof (sdata) exceeds 8.
Don’t require the cookie size to be 8, as this overly fattens
32-bit platforms and one DEADBEEF should be enough.
(GC_STRING_EXTRA): Omit now-unnecessary ‘verify’.
(allocate_string_data): Omit unnecessary cast.
This commit is contained in:
Paul Eggert 2019-04-25 13:42:50 -07:00
parent 69947311d8
commit 83b0fc30d4
1 changed files with 6 additions and 14 deletions
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20
src/alloc.c
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@ -21,7 +21,6 @@ along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include <errno.h>
#include <stdalign.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
@ -1576,16 +1575,15 @@ static struct Lisp_String *string_free_list;
#ifdef GC_CHECK_STRING_OVERRUN
/* We check for overrun in string data blocks by appending a small
/* Check for overrun in string data blocks by appending a small
"cookie" after each allocated string data block, and check for the
presence of this cookie during GC. */
#define GC_STRING_OVERRUN_COOKIE_SIZE 8
# define GC_STRING_OVERRUN_COOKIE_SIZE ROUNDUP (4, alignof (sdata))
static char const string_overrun_cookie[GC_STRING_OVERRUN_COOKIE_SIZE] =
{ '\xde', '\xad', '\xbe', '\xef', '\xde', '\xad', '\xbe', '\xef' };
{ '\xde', '\xad', '\xbe', '\xef', /* Perhaps some zeros here. */ };
#else
#define GC_STRING_OVERRUN_COOKIE_SIZE 0
# define GC_STRING_OVERRUN_COOKIE_SIZE 0
#endif
/* Value is the size of an sdata structure large enough to hold NBYTES
@ -1615,13 +1613,7 @@ static char const string_overrun_cookie[GC_STRING_OVERRUN_COOKIE_SIZE] =
#endif /* not GC_CHECK_STRING_BYTES */
/* Extra bytes to allocate for each string. */
#define GC_STRING_EXTRA (GC_STRING_OVERRUN_COOKIE_SIZE)
/* Make sure that allocating the extra bytes doesn't misalign
`sdata'. */
verify (GC_STRING_EXTRA % alignof (sdata) == 0);
#define GC_STRING_EXTRA GC_STRING_OVERRUN_COOKIE_SIZE
/* Exact bound on the number of bytes in a string, not counting the
terminating NUL. A string cannot contain more bytes than
@ -1882,7 +1874,7 @@ allocate_string_data (struct Lisp_String *s,
data->string = s;
b->next_free = (sdata *) ((char *) data + needed + GC_STRING_EXTRA);
eassert ((uintptr_t) (char *) b->next_free % alignof (sdata) == 0);
eassert ((uintptr_t) b->next_free % alignof (sdata) == 0);
MALLOC_UNBLOCK_INPUT;