On 9/30/19 9:40 PM, Jerry DeLisle wrote:
Copying gcc list for additional thoughts on a possible bogus warning.
On 9/29/19 9:02 AM, Jerry DeLisle wrote:
Hi all,
--- snip ---
diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c
index 4ef35561fdd..fc046efbe34 100644
--- a/libgfortran/io/write.c
+++ b/libgfortran/io/write.c
@@ -1031,7 +1031,7 @@ btoa_big (const char *s, char *buffer, int len,
GFC_UINTEGER_LARGEST *n)
else
{
const char *p = s + len - 1;
- for (i = 0; i < len; i++)
+ for (i = 0; i < len - 1; i++)
{
char c = *p;
--- snip ---
The first attempt to fix (above) is completely off. I have tried
various combinations of code changes and I am beginning to think the
warning is bogus:
In function ‘btoa_big’,
inlined from ‘write_b’ at
../../../trunk/libgfortran/io/write.c:1217:11:
../../../trunk/libgfortran/io/write.c:1052:6: warning: writing 1 byte
into a region of size 0 [-Wstringop-overflow=]
1052 | *q = '\0';
| ~~~^~~~~~
In case it helps, the warning is for the access:
# .MEM_68 = VDEF <.MEM_71>
MEM[(char *)_86] = 0;
where _86 is set to
_86 = &itoa_buf + _43;
and _43 has the range [136, 17179869176]. (The warning needs to
be enhanced a bit to mention the accessed object in this case.)
itoa_buf's DECL_SIZE_UNIT evaluates to 129.
The call to btoa_big in write_b:
p = btoa_big (source, itoa_buf, len, &n);
is made with len > 16. If len > sizeof itoa_buf / 8 then it does
look like btoa_big would write past the end of itoa_buf because it
writes len * 8 bytes into it. I don't know if the function can be
called with len that large but if not, adding this just above
the call suppresses the warning.
if (len > sizeof itoa_buf / 8)
__builtin_unreachable ();
Martin
Using gdb I have watched the pointer address stored in q and the setting
of the string of bytes doing the binary to ascii conversion. I have also
checked the length of the buffer being used and its is what I would
expect with length of 129.
However, the warning only goes away if I add an additional 8 bytes to
the buffer (suspicious).
So doing the following eliminates the warning:
diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c
index 4ef35561fdd..fd0e46851e4 100644
--- a/libgfortran/io/write.c
+++ b/libgfortran/io/write.c
@@ -1204,7 +1204,7 @@ void
write_b (st_parameter_dt *dtp, const fnode *f, const char *source, int
len)
{
const char *p;
- char itoa_buf[GFC_BTOA_BUF_SIZE];
+ char itoa_buf[GFC_BTOA_BUF_SIZE + 8];
GFC_UINTEGER_LARGEST n = 0;
if (len > (int) sizeof (GFC_UINTEGER_LARGEST))
Any suggestions? I am certainly not seeing it.
Regards,
Jerry
