[PATCH] Clear upper bits during sign extension
Yao Qi
yao@codesourcery.com
Mon Dec 29 06:27:00 GMT 2014
Doug Evans <dje@google.com> writes:
> It's not immediately clear to this reader that undefined behaviour is
> avoided here.
> E.g., what if sizeof (LONGEST) == 8 && bit == 64.
How about returning VALUE simply in this case? like the patch below,
--
Yao (齐尧)
gdb:
2014-12-29 Yao Qi <yao@codesourcery.com>
* utils.c (gdb_sign_extend): Do sign extension if BIT is less
than 8 * sizeof (LONGEST). Clear bits from BIT in VALUE.
diff --git a/gdb/utils.c b/gdb/utils.c
index 47adb67..83a6df6 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -3028,10 +3028,13 @@ gdb_sign_extend (LONGEST value, int bit)
{
gdb_assert (bit >= 1 && bit <= 8 * sizeof (LONGEST));
- if (((value >> (bit - 1)) & 1) != 0)
+ if (bit < 8 * sizeof (LONGEST) && ((value >> (bit - 1)) & 1) != 0)
{
LONGEST signbit = ((LONGEST) 1) << (bit - 1);
+ /* Clear upper bits from bit BIT. */
+ value &= (signbit << 1) - 1;
+
value = (value ^ signbit) - signbit;
}
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