[Bug c/101854] New: Invalid warning -Wstringop-overflow wrong argument

[Bug c/101854] New: Invalid warning -Wstringop-overflow wrong argument

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

            Bug ID: 101854
           Summary: Invalid warning -Wstringop-overflow wrong argument
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nightstrike at gmail dot com
  Target Milestone: ---

void f() {
        struct Weird {
                float a; // Comment out any member
                float b; // to silence the warning
                float c;
                float d;
                float e;
        };
        struct Weird g(float const Q[2], float const null[6][8]) {
                return (struct Weird){0};
        }

        float const q[2];
        struct Weird ss = g(q, (void *)0);
}

$ gcc -c a.c
a.c: In function 'f':
a.c:14:27: warning: 'g' accessing 192 bytes in a region of size 8
[-Wstringop-overflow=]
   14 |         struct Weird ss = g(q, (void *)0);
      |                           ^~~~~~~~~~~~~~~
a.c:14:27: note: referencing argument 2 of type 'const float (*)[8]'
a.c:9:22: note: in a call to function 'g'
    9 |         struct Weird g(float const Q[2], float const null[6][8]) {
      |                      ^


$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/tmp/bin/../libexec/gcc/x86_64-pc-linux-gnu/11.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../src/gcc-11.2.0/configure --disable-nls --disable-multilib
--enable-languages=all --prefix=/tmp
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.2.0 (GCC)

[Bug tree-optimization/101854] Invalid warning -Wstringop-overflow wrong argument

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Slightly more reduced:
void f() {
        struct Weird {
                float a[5]; // decrease to 4 will cause the warning to
disappear
        };
        struct Weird g(float const Q[2], float const null[6][8]) {
                return (struct Weird){0};
        }

        float const q[2];
        struct Weird ss = g(q, (void *)0);
}

[Bug c/101854] Invalid warning -Wstringop-overflow wrong argument

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

nightstrike <nightstrike at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|tree-optimization           |c
           Keywords|diagnostic                  |

--- Comment #2 from nightstrike <nightstrike at gmail dot com> ---
So to clarify, the "192 bytes" is the size of the flagged argument #2.  The
"size 8" is the size of the first argument.  If you change q and Q to be 3
elements, then size is 12, etc.

[Bug tree-optimization/101854] Invalid warning -Wstringop-overflow wrong argument

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So this is not related to nested functions at all (just in case people thought
it was):
struct Weird {
        float a[5]; // decrease to 4 will cause the warning to disappear
};
struct Weird g(float const Q[2], float const null[6][8]) {
        return (struct Weird){0};
}
void f() {
        float const q[2]={0};
        struct Weird ss = g(q, (void *)0);
}

[Bug tree-optimization/101854] Invalid warning -Wstringop-overflow wrong argument

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #4 from nightstrike <nightstrike at gmail dot com> ---
(In reply to Andrew Pinski from comment #3)
> So this is not related to nested functions at all (just in case people
> thought it was):

It's also not due to flexible array members, given the change from 5 members to
an array. I only mention it because I've submitted a report in the past about a
different warning that was affected by that feature of C.

[Bug tree-optimization/101854] Invalid warning -Wstringop-overflow wrong argument

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
__attribute__((access ("^0[2]^1[6]", )))
struct Weird g (const float * Q, const float[8] * null)

  ss = g (&q, 0B); [return slot optimization]

[Bug tree-optimization/101854] [11/12 Regression] Invalid warning -Wstringop-overflow wrong argument

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Invalid warning             |[11/12 Regression] Invalid
                   |-Wstringop-overflow wrong   |warning -Wstringop-overflow
                   |argument                    |wrong argument
   Target Milestone|---                         |11.3

[Bug tree-optimization/101854] [11/12 Regression] Invalid warning -Wstringop-overflow wrong argument

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #5)
> __attribute__((access ("^0[2]^1[6]", )))
> struct Weird g (const float * Q, const float[8] * null)
> 
>   ss = g (&q, 0B); [return slot optimization]

In the 4 case we get:
  ss = g (&q, 0B);

So no RSO.
So yes the code looks like it is counting wrong somewhere.

[Bug tree-optimization/101854] [11/12 Regression] Invalid warning -Wstringop-overflow wrong argument

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org
   Last reconfirmed|                            |2021-08-12
             Blocks|                            |88443
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #7 from Martin Sebor <msebor at gcc dot gnu.org> ---
Below is a further simplified test case.  The code in
initialize_argument_information() that computes the sizes of actual arguments
to array parameters and issues a warning if the former is less than expected
doesn't consider the implicit pointer argument passed to functions that return
structs by value.  It's off by one for those.

$ cat t.c && gcc -S -Wall t.c
struct A { int a[5]; };

struct A g (int*, int[6][8]);

struct A f (void)
{
  int a[2];
  return g (a, 0);
}

t.c: In function ‘f’:
t.c:8:10: warning: ‘g’ accessing 192 bytes in a region of size 8
[-Wstringop-overflow=]
    8 |   return g (a, 0);
      |          ^~~~~~~~
t.c:8:10: note: referencing argument 2 of type ‘int (*)[8]’
t.c:3:10: note: in a call to function ‘g’
    3 | struct A g (int*, int[6][8]);
      |          ^


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88443
[Bug 88443] [meta-bug] bogus/missing -Wstringop-overflow warnings

[Bug tree-optimization/101854] [11/12 Regression] Invalid warning -Wstringop-overflow wrong argument

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug tree-optimization/101854] [11/12 Regression] Invalid warning -Wstringop-overflow wrong argument

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>:

https://gcc.gnu.org/g:b48d4e6818674898f90d9358378c127511ef0f9f

commit r12-2976-gb48d4e6818674898f90d9358378c127511ef0f9f
Author: Martin Sebor <msebor@redhat.com>
Date:   Tue Aug 17 14:49:05 2021 -0600

    Move more warning code to gimple-ssa-warn-access etc.

    Also resolves:
    PR middle-end/101854 - Invalid warning -Wstringop-overflow wrong argument

    gcc/ChangeLog:

            PR middle-end/101854
            * builtins.c (expand_builtin_alloca): Move warning code to
check_alloca
            in gimple-ssa-warn-access.cc.
            * calls.c (alloc_max_size): Move code to check_alloca.
            (get_size_range): Move to pointer-query.cc.
            (maybe_warn_alloc_args_overflow): Move to
gimple-ssa-warn-access.cc.
            (get_attr_nonstring_decl): Move to tree.c.
            (fntype_argno_type): Move to gimple-ssa-warn-access.cc.
            (append_attrname): Same.
            (maybe_warn_rdwr_sizes): Same.
            (initialize_argument_information): Move code to
            gimple-ssa-warn-access.cc.
            * calls.h (maybe_warn_alloc_args_overflow): Move to
            gimple-ssa-warn-access.h.
            (get_attr_nonstring_decl): Move to tree.h.
            (maybe_warn_nonstring_arg):  Move to gimple-ssa-warn-access.h.
            (enum size_range_flags): Move to pointer-query.h.
            (get_size_range): Same.
            * gimple-ssa-warn-access.cc (has_location): Remove unused overload
            to avoid Clang -Wunused-function.
            (get_size_range): Declare static.
            (maybe_emit_free_warning): Rename...
            (maybe_check_dealloc_call): ...to this for consistency.
            (class pass_waccess): Add members.
            (pass_waccess::~pass_waccess): Defined.
            (alloc_max_size): Move here from calls.c.
            (maybe_warn_alloc_args_overflow): Same.
            (check_alloca): New function.
            (check_alloc_size_call): New function.
            (check_strncat): Handle another warning flag.
            (pass_waccess::check_builtin): Handle alloca.
            (fntype_argno_type): Move here from calls.c.
            (append_attrname): Same.
            (maybe_warn_rdwr_sizes): Same.
            (pass_waccess::check_call): Define.
            (check_nonstring_args): New function.
            (pass_waccess::check): Call new member functions.
            (pass_waccess::execute): Enable ranger.
            * gimple-ssa-warn-access.h (get_size_range): Move here from
calls.h.
            (maybe_warn_nonstring_arg): Same.
            * gimple-ssa-warn-restrict.c: Remove #include.
            * pointer-query.cc (get_size_range): Move here from calls.c.
            * pointer-query.h (enum size_range_flags): Same.
            (get_size_range): Same.
            * tree.c (get_attr_nonstring_decl): Move here from calls.c.
            * tree.h (get_attr_nonstring_decl): Move here from calls.h.

    gcc/testsuite/ChangeLog:

            * gcc.dg/attr-alloc_size-5.c: Adjust optimization to -O1.
            * gcc.dg/attr-alloc_size-7.c: Use #pragmas to adjust optimization.
            * gcc.dg/attr-alloc_size-8.c: Adjust optimization to -O1.

            PR middle-end/101854
            * gcc.dg/Wstringop-overflow-72.c: New test.

[Bug tree-optimization/101854] [11 Regression] Invalid warning -Wstringop-overflow wrong argument

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12 Regression] Invalid  |[11 Regression] Invalid
                   |warning -Wstringop-overflow |warning -Wstringop-overflow
                   |wrong argument              |wrong argument
      Known to fail|                            |11.2.0

--- Comment #9 from Martin Sebor <msebor at gcc dot gnu.org> ---
Fixed for GCC 12.  The patch is far too intrusive to backport but the following
should fix the problem in GCC 11:

diff --git a/gcc/calls.c b/gcc/calls.c
index fcb0d6dec69..f116923c890 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -2295,14 +2295,15 @@ initialize_argument_information (int num_actuals
ATTRIBUTE_UNUSED,
         operand for later processing.  */
       if (attr_access *access = rdwr_idx.get (argpos))
        {
+         int idx = i - !!struct_value_addr_value;
          if (POINTER_TYPE_P (type))
            {
-             access->ptr = args[i].tree_value;
+             access->ptr = args[idx].tree_value;
              // A nonnull ACCESS->SIZE contains VLA bounds.  */
            }
          else
            {
-             access->size = args[i].tree_value;
+             access->size = args[idx].tree_value;
              gcc_assert (access->ptr == NULL_TREE);
            }
        }

[Bug tree-optimization/101854] [11 Regression] Invalid warning -Wstringop-overflow wrong argument

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.3                        |11.4

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.3 is being released, retargeting bugs to GCC 11.4.

[Bug tree-optimization/101854] [11 Regression] Invalid warning -Wstringop-overflow wrong argument

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

--- Comment #11 from nightstrike <nightstrike at gmail dot com> ---
(In reply to Martin Sebor from comment #9)
> Fixed for GCC 12.  The patch is far too intrusive to backport but the
> following should fix the problem in GCC 11:

Would you mind applying it to 11?  Thanks!

Also, I think in your diff below, there's "// A nonnull" that should be "/* A
nonnull"... / to *

> diff --git a/gcc/calls.c b/gcc/calls.c
> index fcb0d6dec69..f116923c890 100644
> --- a/gcc/calls.c
> +++ b/gcc/calls.c
> @@ -2295,14 +2295,15 @@ initialize_argument_information (int num_actuals
> ATTRIBUTE_UNUSED,
>          operand for later processing.  */
>        if (attr_access *access = rdwr_idx.get (argpos))
>         {
> +         int idx = i - !!struct_value_addr_value;
>           if (POINTER_TYPE_P (type))
>             {
> -             access->ptr = args[i].tree_value;
> +             access->ptr = args[idx].tree_value;
>               // A nonnull ACCESS->SIZE contains VLA bounds.  */
>             }
>           else
>             {
> -             access->size = args[i].tree_value;
> +             access->size = args[idx].tree_value;
>               gcc_assert (access->ptr == NULL_TREE);
>             }
>         }

[Bug tree-optimization/101854] [11 Regression] Invalid warning -Wstringop-overflow wrong argument

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101854

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.4                        |11.5

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 11.4 is being released, retargeting bugs to GCC 11.5.