https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111049
Bug ID: 111049
Summary: spurious stringop-overflow depending on structure
pointer arithmetic with certain sized structures
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: mark at infocomm dot com
Target Milestone: ---
Created attachment 55746
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55746&action=edit
C source that demonstrates the problem
These warnings are incorrectly reported and have somewhat meaningless content:
In function ‘xxx_set_array’,
inlined from ‘xxx_b’ at ptr_diff_err.c:177:5:
ptr_diff_err.c:189:23: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
189 | xxx_array[u][l++] = (code >> i) & 1;
| ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
ptr_diff_err.c: In function ‘xxx_b’:
ptr_diff_err.c:94:16: note: at offset [-10324440, 10324440] to object
‘xxx_array’ with size 3192 declared here
94 | static uint8_t xxx_array[2][1596];
| ^~~~~~~~~
In function ‘xxx_set_array’,
inlined from ‘xxx_b’ at ptr_diff_err.c:177:5:
ptr_diff_err.c:189:23: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
189 | xxx_array[u][l++] = (code >> i) & 1;
| ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
ptr_diff_err.c: In function ‘xxx_b’:
ptr_diff_err.c:94:16: note: at offset 0 to object ‘xxx_array’ with size 3192
declared here
94 | static uint8_t xxx_array[2][1596];
| ^~~~~~~~~
In function ‘xxx_set_array’,
inlined from ‘xxx_b’ at ptr_diff_err.c:177:5:
ptr_diff_err.c:189:23: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
189 | xxx_array[u][l++] = (code >> i) & 1;
| ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
ptr_diff_err.c: In function ‘xxx_b’:
What does "offset [-10324440, 10324440] to object" mean?
What does "a region of size 0" mean?
This occurs with: gcc (Raspbian 10.2.1-6+rpi1) 10.2.1 20210110
On: Linux raspberrypi 6.1.21-v7+ #1642 SMP Mon Apr 3 17:20:52 BST 2023 armv7l
GNU/Linux
These warnings only happen when compiling with -O2
These warnings only happen when the value u mentioned on line 189 is produced
by simple pointer arithmetic between elements of the same array of structures.
They ONLY happen when the structure has certain sizes and not when that
structure has other sizes. The attached source file can be compiled to
demonstrate the problem with different sized structures.
See comments at the top of the attach example file which describe how to change
the compile time structure size with -DSTR_EXTRAS= and which values generate
the messages and which values do not.
