[Bug middle-end/92939] missing -Wstringop-overflow on negative index from the end of array

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92939

Martin Sebor  changed:

   What|Removed |Added

  Known to fail||10.1.0
 Status|UNCONFIRMED |RESOLVED
   Target Milestone|--- |11.0
  Known to work||11.0
 Resolution|--- |FIXED
   Assignee|unassigned at gcc dot gnu.org  |msebor at gcc dot 
gnu.org

--- Comment #2 from Martin Sebor  ---
After r11-1183 GCC detects the overflow as expected:

$ gcc -O2 -S -Wall -Wextra -Wno-array-bounds pr92939.c

pr92939.c: In function ‘f’:
pr92939.c:12:8: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
   12 |   p[1] = 0;// a[3]a[3] a[4]a[4]<< warns
  |   ~^~~
pr92939.c:8:8: note: at offset 3 to object ‘a’ with size 3 declared here
8 |   char a[3], *p = a + n;
  |^
pr92939.c:22:9: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
   22 |   p[-2] = 0;   // a[-2]   a[-3]a[-1]   a[-2]   << should warn
  |   ~~^~~
pr92939.c:8:8: note: at offset -1 to object ‘a’ with size 3 declared here
8 |   char a[3], *p = a + n;
  |^

[Bug middle-end/92939] missing -Wstringop-overflow on negative index from the end of array

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92939

--- Comment #1 from CVS Commits  ---
The master branch has been updated by Martin Sebor :

https://gcc.gnu.org/g:a2c2cee92e5defff9bf23d3b1184ee96e57e5fdd

commit r11-1183-ga2c2cee92e5defff9bf23d3b1184ee96e57e5fdd
Author: Martin Sebor 
Date:   Wed Jun 10 12:00:08 2020 -0600

PR middle-end/95353 - spurious -Wstringop-overflow writing to a trailing
array plus offset

Also resolves:
PR middle-end/92939 - missing -Wstringop-overflow on negative index from
the end of array

gcc/ChangeLog:

PR middle-end/95353
PR middle-end/92939
* builtins.c (inform_access): New function.
(check_access): Call it.  Add argument.
(addr_decl_size): Remove.
(get_range): New function.
(compute_objsize): New overload.  Only use
compute_builtin_object_size
with raw memory function.
(check_memop_access): Pass new argument to compute_objsize and
check_access.
(expand_builtin_memchr, expand_builtin_strcat): Same.
(expand_builtin_strcpy, expand_builtin_stpcpy_1): Same.
(expand_builtin_stpncpy, check_strncat_sizes): Same.
(expand_builtin_strncat, expand_builtin_strncpy): Same.
(expand_builtin_memcmp): Same.
* builtins.h (check_nul_terminated_array): Declare extern.
(check_access): Add argument.
(struct access_ref, struct access_data): New structs.
* gimple-ssa-warn-restrict.c (clamp_offset): New helper.
(builtin_access::overlap): Call it.
* tree-object-size.c (decl_init_size): Declare extern.
(addr_object_size): Correct offset computation.
* tree-object-size.h (decl_init_size): Declare.
* tree-ssa-strlen.c (handle_integral_assign): Remove a call
to maybe_warn_overflow when assigning to an SSA_NAME.

gcc/testsuite/ChangeLog:

PR middle-end/95353
PR middle-end/92939
* c-c++-common/Wstringop-truncation.c: Remove an xfail.
* gcc.dg/Warray-bounds-46.c: Remove a bogus warning.
* gcc.dg/Wrestrict-9.c: Disable -Wstringop-overflow.
* gcc.dg/Wstringop-overflow-12.c: Remove xfails.
* gcc.dg/Wstringop-overflow-28.c: Same.
* gcc.dg/builtin-stringop-chk-4.c: Same.
* gcc.dg/builtin-stringop-chk-5.c: Same.
* gcc.dg/builtin-stringop-chk-8.c: Same.
* gcc.dg/strlenopt-74.c: Avoid buffer overflow.
* gcc.dg/Wstringop-overflow-34.c: New test.
* gcc.dg/Wstringop-overflow-35.c: New test.
* gcc.dg/Wstringop-overflow-36.c: New test.
* gcc.dg/Wstringop-overflow-37.c: New test.
* gcc.dg/Wstringop-overflow-38.c: New test.