[Bug target/108189] New: anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[Bug target/108189] New: anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[james.hilliard1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

            Bug ID: 108189
           Summary: anonymous struct declared inside parameter list will
                    not be visible outside of this definition or
                    declaration
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: james.hilliard1 at gmail dot com
  Target Milestone: ---

I'm seeing this error which does not occur in llvm for a bpf
test(btf_dump_test_case_bitfields.c) in bpf-next:

progs/btf_dump_test_case_bitfields.c:85:7: error: anonymous struct declared
inside parameter list will not be visible outside of this definition or
declaration [-Werror]
   85 | int f(struct {
      |       ^~~~~~

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The error is correct at least for C before C23.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[james.hilliard1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #2 from James Hilliard <james.hilliard1 at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> The error is correct at least for C before C23.

Hmm, seeing it with -std=gnu2x passed still:
/home/buildroot/opt/cross/bin/bpf-gcc  -g -Werror -D__TARGET_ARCH_x86
-mlittle-endian
-I/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include
-I/home/buildroot/bpf-next/tools/testing/selftests/bpf/tools/include
-I/home/buildroot/bpf-next/tools/testing/selftests/bpf
-I/home/buildroot/bpf-next/tools/include/uapi
-I/home/buildroot/bpf-next/tools/testing/selftests/usr/include -gbtf -mco-re
-Wno-error=attributes -Wno-error=address-of-packed-member
-Wno-compare-distinct-pointer-types -std=gnu2x -idirafter
/usr/lib/gcc/x86_64-linux-gnu/11/include -idirafter /usr/local/include
-idirafter /usr/include/x86_64-linux-gnu -idirafter /usr/include  -nostdinc -O2
-c progs/btf_dump_test_case_bitfields.c -mcpu=v3 -o
/home/buildroot/bpf-next/tools/testing/selftests/bpf/bpf_gcc/btf_dump_test_case_bitfields.bpf.o
progs/btf_dump_test_case_bitfields.c:85:7: error: anonymous struct declared
inside parameter list will not be visible outside of this definition or
declaration [-Werror]
   85 | int f(struct {
      |       ^~~~~~

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC does not implement all of C2X yet.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Also Clang does not implement this warning at all.

It is a bug in bpf-next really.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Also Clang does not implement this warning at all.

It is a bug in bpf-next really.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |MOVED

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
clang does not implement the warning even though it is a correct warning.
Witness:
int f(struct {int t;} b)
{
  return b.t;
}

int f1(void)
{
  return f((struct {int t;}){1});
}
Is rejected.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Yes the warning is really still correct even if a closer testcase would be:
```
int f(struct {int t;} *b)
{
  return b->t;
}

int f1(void *a)
{
  return f(a);
}
```
I am actually shocked clang didn't implement this warning since there is no
type which is compatible with the typeof *b outside of function f.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[james.hilliard1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #8 from James Hilliard <james.hilliard1 at gmail dot com> ---
(In reply to Andrew Pinski from comment #7)
> Yes the warning is really still correct even if a closer testcase would be:
> ```
> int f(struct {int t;} *b)
> {
>   return b->t;
> }
> 
> int f1(void *a)
> {
>   return f(a);
> }
> ```
> I am actually shocked clang didn't implement this warning since there is no
> type which is compatible with the typeof *b outside of function f.

Yeah, clang with -std=gnu17 -pedantic doesn't even complain at all from the
looks of it. Does it make sense to allow disabling this specific warning in
GCC?

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[james.hilliard1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #9 from James Hilliard <james.hilliard1 at gmail dot com> ---
(In reply to Andrew Pinski from comment #5)
> Also Clang does not implement this warning at all.
> 
> It is a bug in bpf-next really.

What would be the correct way to fix these in bpf-next?

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to James Hilliard from comment #8) 
> Yeah, clang with -std=gnu17 -pedantic doesn't even complain at all from the
> looks of it. Does it make sense to allow disabling this specific warning in
> GCC?

No it does not make sense at all to disable this specific warning; maybe
request clang implement the warning too.

> What would be the correct way to fix these in bpf-next?

Move the struct definition outside of the function definition? You could ask
the bpf mailing list of what is the fix they would like to see for this
questionable code.

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[james.hilliard1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #11 from James Hilliard <james.hilliard1 at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> The error is correct at least for C before C23.

Can you clarify where exactly in the C23 specification that this will be
allowed?

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[dxu at dxuuu dot xyz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

Daniel Xu <dxu at dxuuu dot xyz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dxu at dxuuu dot xyz

--- Comment #12 from Daniel Xu <dxu at dxuuu dot xyz> ---
I was fighting this warning as well (for bpftrace tests).

I believe the part of the C23 standard being referred
to is https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3037.pdf

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[jemarch at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #13 from Jose E. Marchesi <jemarch at gcc dot gnu.org> ---
In bpf-next we are passing -Wno-error for the particular BPF selftests that use
this construct:

progs/btf_dump_test_case_bitfields.c-CFLAGS := -Wno-error
progs/btf_dump_test_case_namespacing.c-CFLAGS := -Wno-error
progs/btf_dump_test_case_packing.c-CFLAGS := -Wno-error
progs/btf_dump_test_case_padding.c-CFLAGS := -Wno-error
progs/btf_dump_test_case_syntax.c-CFLAGS := -Wno-error

[Bug target/108189] anonymous struct declared inside parameter list will not be visible outside of this definition or declaration

[dxu at dxuuu dot xyz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108189

--- Comment #14 from Daniel Xu <dxu at dxuuu dot xyz> ---
Yeah, I saw that. But that only makes the build not
fail right? For bpftrace we are trying hard to be
warning-free.

FWIW I tried adding `-std=gnu2x` and it didn't help.