[Bug target/107843] New: error: incompatible type for argument in ___bpf_ctx_cast2

[Bug target/107843] New: error: incompatible type for argument in ___bpf_ctx_cast2

[james.hilliard1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107843

            Bug ID: 107843
           Summary: error: incompatible type for argument in
                    ___bpf_ctx_cast2
           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(bpf_cubic.c)
in bpf-next:

In file included from
/home/buildroot/bpf-next/tools/testing/selftests/bpf/bpf_tcp_helpers.h:9,
                 from progs/bpf_cubic.c:20:
progs/bpf_cubic.c: In function 'bpf_cubic_cwnd_event':
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_tracing.h:399:63:
error: incompatible type for argument 3 of '____bpf_cubic_cwnd_event'
  399 | #define ___bpf_ctx_cast2(x, args...)  ___bpf_ctx_cast1(args), (void
*)ctx[1]
      |                                                              
^~~~~~~~~~~~~~
      |                                                               |
      |                                                               void *
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_helpers.h:187:29:
note: in expansion of macro '___bpf_ctx_cast2'
  187 | #define ___bpf_concat(a, b) a ## b
      |                             ^
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_helpers.h:190:29:
note: in expansion of macro '___bpf_concat'
  190 | #define ___bpf_apply(fn, n) ___bpf_concat(fn, n)
      |                             ^~~~~~~~~~~~~
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_tracing.h:410:39:
note: in expansion of macro '___bpf_apply'
  410 | #define ___bpf_ctx_cast(args...)      ___bpf_apply(___bpf_ctx_cast,
___bpf_narg(args))(args)
      |                                       ^~~~~~~~~~~~
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_tracing.h:435:27:
note: in expansion of macro '___bpf_ctx_cast'
  435 |         return ____##name(___bpf_ctx_cast(args));                      
    \
      |                           ^~~~~~~~~~~~~~~
progs/bpf_cubic.c:189:6: note: in expansion of macro 'BPF_PROG'
  189 | void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event
event)
      |      ^~~~~~~~
progs/bpf_cubic.c:189:72: note: expected 'enum tcp_ca_event' but argument is of
type 'void *'
  189 | void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event
event)
      |                                                     
~~~~~~~~~~~~~~~~~~^~~~~
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_tracing.h:430:39:
note: in definition of macro 'BPF_PROG'
  430 | ____##name(unsigned long long *ctx, ##args);                           
    \
      |                                       ^~~~
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_tracing.h:435:16:
error: 'return' with a value, in function returning void [-Werror]
  435 |         return ____##name(___bpf_ctx_cast(args));                      
    \
      |                ^~~~
progs/bpf_cubic.c:189:6: note: in expansion of macro 'BPF_PROG'
  189 | void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event
event)
      |      ^~~~~~~~
progs/bpf_cubic.c:189:15: note: declared here
  189 | void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event
event)
      |               ^~~~~~~~~~~~~~~~~~~~
/home/buildroot/bpf-next/tools/bpf/resolve_btfids/libbpf/include/bpf/bpf_tracing.h:431:17:
note: in definition of macro 'BPF_PROG'
  431 | typeof(name(0)) name(unsigned long long *ctx)                          
    \
      |

[Bug target/107843] error: incompatible type for argument in ___bpf_ctx_cast2

[david.faust at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107843

--- Comment #1 from David Faust <david.faust at oracle dot com> ---
Looks like this is an issue with passing void* where an enum type is
expected in a function call. This is not specific to the BPF backend.

Not entirely clear to me whether this is expected or a bug, but it
does differ from llvm behavior.

Reproducer below, tried with a few gccs, same behavior:
today (6 Dec 2022)'s master 81476bc4f4a20bcf3af7ac2548c2322d48499402
gcc-12 (Debian 12.2.0-9) 12.2.0
gcc-10 (Debian 10.4.0-5) 10.4.0
gcc-8 (Debian 8.4.0-7) 8.4.0

$ cat enumcast.c
enum E {
  E_FOO = 0,
  E_BAR = 1,
};

int foo_enum (enum E e);

int bar_enum (enum E e) {
  return foo_enum ((void *) e);
}

int foo_int (int x);

int bar_int (int x) {
  return foo_int ((void *) x);
}


$ gcc -c enumcast.c -o enumcast.o
enumcast.c: In function ‘bar_enum’:
enumcast.c:10:20: error: incompatible type for argument 1 of ‘foo_enum’
   10 |   return foo_enum ((void *) e);
      |                    ^~~~~~~~~~
      |                    |
      |                    void *
enumcast.c:7:22: note: expected ‘enum E’ but argument is of type ‘void *’
    7 | int foo_enum (enum E e);
      |               ~~~~~~~^
enumcast.c: In function ‘bar_int’:
enumcast.c:16:19: warning: cast to pointer from integer of different size
[-Wint-to-pointer-cast]
   16 |   return foo_int ((void *) x);
      |                   ^
enumcast.c:16:19: warning: passing argument 1 of ‘foo_int’ makes integer from
pointer without a cast [-Wint-conversion]
   16 |   return foo_int ((void *) x);
      |                   ^~~~~~~~~~
      |                   |
      |                   void *
enumcast.c:13:18: note: expected ‘int’ but argument is of type ‘void *’
   13 | int foo_int (int x);
      |              ~~~~^


$ clang -c enumcast.c -o enumcast.o
enumcast.c:10:20: warning: incompatible pointer to integer conversion passing
'void *' to parameter of type 'enum E' [-Wint-conversion]
  return foo_enum ((void *) e);
                   ^~~~~~~~~~
enumcast.c:7:22: note: passing argument to parameter 'e' here
int foo_enum (enum E e);
                     ^
enumcast.c:16:19: warning: cast to 'void *' from smaller integer type 'int'
[-Wint-to-void-pointer-cast]
  return foo_int ((void *) x);
                  ^~~~~~~~~~
enumcast.c:16:19: warning: incompatible pointer to integer conversion passing
'void *' to parameter of type 'int' [-Wint-conversion]
  return foo_int ((void *) x);
                  ^~~~~~~~~~
enumcast.c:13:18: note: passing argument to parameter 'x' here
int foo_int (int x);
                 ^
3 warnings generated.

[Bug target/107843] error: incompatible type for argument in ___bpf_ctx_cast2

[jemarch at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107843

Jose E. Marchesi <jemarch at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-01-06
     Ever confirmed|0                           |1

--- Comment #2 from Jose E. Marchesi <jemarch at gcc dot gnu.org> ---
Opened a clang/llvm bug for this, to see if they would consider turning the
warning into an error to converge with GCC's behavior.

https://github.com/llvm/llvm-project/issues/59858

[Bug target/107843] error: incompatible type for argument in ___bpf_ctx_cast2

[jemarch at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107843

Jose E. Marchesi <jemarch at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #3 from Jose E. Marchesi <jemarch at gcc dot gnu.org> ---
clang/llvm confirms that clang 15 behaves like GCC, emitting the same error.
So I am closing this issue.