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tree-object-size: Fall back to wholesize for non-const offset

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Don't bail out early if the offset to a pointer in __builtin_object_size
is a variable, return the wholesize instead since that is a better
fallback for maximum estimate.  This should keep checks in place for
fortified functions to constrain overflows to at lesat some extent.

gcc/ChangeLog:

	PR middle-end/77608
	* tree-object-size.cc (plus_stmt_object_size): Drop check for
	constant offset.

gcc/testsuite/ChangeLog:

	* gcc.dg/builtin-object-size-1.c (test12): New test.
	(main): Call it.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>
This commit is contained in:
Siddhesh Poyarekar 2024-09-18 22:36:09 -04:00
parent b12c9ce245
commit 51b85dfeb1
2 changed files with 24 additions and 3 deletions
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21
gcc/testsuite/gcc.dg/builtin-object-size-1.c
View file

@ -712,6 +712,25 @@ test11 (void)
}
#endif
void
__attribute__ ((noinline))
test12 (unsigned off)
{
char *buf2 = malloc (10);
char *p;
size_t t;
p = &buf2[off];
#ifdef __builtin_object_size
if (__builtin_object_size (p, 0) != 10 - off)
FAIL ();
#else
if (__builtin_object_size (p, 0) != 10)
FAIL ();
#endif
}
int
main (void)
{
@ -730,5 +749,7 @@ main (void)
#ifndef SKIP_STRNDUP
test11 ();
#endif
test12 (0);
test12 (2);
DONE ();
}

6
gcc/tree-object-size.cc
View file

@ -1501,8 +1501,7 @@ plus_stmt_object_size (struct object_size_info *osi, tree var, gimple *stmt)
return false;
/* Handle PTR + OFFSET here. */
if (size_valid_p (op1, object_size_type)
&& (TREE_CODE (op0) == SSA_NAME || TREE_CODE (op0) == ADDR_EXPR))
if ((TREE_CODE (op0) == SSA_NAME || TREE_CODE (op0) == ADDR_EXPR))
{
if (TREE_CODE (op0) == SSA_NAME)
{
@ -1528,7 +1527,8 @@ plus_stmt_object_size (struct object_size_info *osi, tree var, gimple *stmt)
;
else if ((object_size_type & OST_DYNAMIC)
|| bytes != wholesize
|| compare_tree_int (op1, offset_limit) <= 0)
|| (size_valid_p (op1, object_size_type)
&& compare_tree_int (op1, offset_limit) <= 0))
bytes = size_for_offset (bytes, op1, wholesize);
/* In the static case, with a negative offset, the best estimate for
minimum size is size_unknown but for maximum size, the wholesize is a