Re: [PATCH bpf-next v1 04/10] resolve_btfids: Support for KF_IMPLICIT_ARGS

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 1/12/26 8:51 AM, Andrii Nakryiko wrote:
> On Fri, Jan 9, 2026 at 5:15 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>>
>> [...]
>>>>
>>>> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
>>>> index df39982f51df..b361e726fa36 100644
>>>> --- a/tools/bpf/resolve_btfids/main.c
>>>> +++ b/tools/bpf/resolve_btfids/main.c
>>>> @@ -152,6 +152,18 @@ struct object {
>>>>         int nr_typedefs;
>>>>  };
>>>>
>>>> +#define KF_IMPLICIT_ARGS (1 << 16)
>>>> +#define KF_IMPL_SUFFIX "_impl"
>>>> +#define MAX_BPF_FUNC_REG_ARGS 5
>>>> +#define MAX_KFUNCS 256
>>>> +#define MAX_DECL_TAGS (MAX_KFUNCS * 4)
>>>
>>> can't we get that from include/linux/bpf.h? seems like
>>> resolve_btfids's main.c include internal headers just fine, so why
>>> duplicate definitions?
>>
>> Hi Andrii, thank you for a quick review.
>>
>> Including internal include/linux/btf.h directly doesn't work, which is
>> probably expected.
>>
>> resolve_btfids is currently built with:
>>
>> HOSTCFLAGS_resolve_btfids += -g \
>>           -I$(srctree)/tools/include \
>>           -I$(srctree)/tools/include/uapi \
> 
> so I don't know if that will solve the issue, but I don't think it
> makes sense to build resolve_btfids using tools' version of includes.
> tools/include is mostly for perf's benefit (maybe so that they don't
> accidentally take some kernel-internal dependency, not sure). But
> resolve_btfids is built for the kernel during the kernel build, we
> should have access to full kernel headers. Try changing this and see
> if build errors go away?
> 
>>           -I$(LIBBPF_INCLUDE) \
>>           -I$(SUBCMD_INCLUDE) \
>>           $(LIBELF_FLAGS) \
>>           -Wall -Werror
>>
>> If I add -I$(srctree)/include option and then
>>
>>     #include <linux/btf.h>
>>
>> A bunch of build errors happen.
>>
>> AFAIU we'd have to create a stripped copy of relevant headers in
>> tools/include first.  Is that what you're suggesting?
> 
> see above, the opposite -- just use -I$(srctree)/include directly

Andrii,

I made a low-effort attempt to switch away from tools/include and it
looks like too much trouble. See a sample splat below.

I think the issue is that resolve_btfids uses a couple of inherently
user-space things (stdlib, libelf), which themselves may include
system headers. And there is actually a difference between the kernel
and tools/include headers. For example, check

  ./include/linux/rbtree.h
vs
  ./tools/include/linux/rbtree.h

Maybe we can make it work (with our own local tools/include?), but it
doesn't look worth it for just a couple of constant #define-s.

Let me know if I am missing something.


$ make
  INSTALL libsubcmd_headers
  HOSTCC  /home/isolodrai/workspace/prog-aux/linux/tools/bpf/resolve_btfids/main.o
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:20:33: error: conflicting types for ‘fd_set’; have ‘__kernel_fd_set’
   20 | typedef __kernel_fd_set         fd_set;
      |                                 ^~~~~~
In file included from /usr/include/sys/types.h:179,
                 from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/sys/select.h:70:5: note: previous declaration of ‘fd_set’ with type ‘fd_set’
   70 |   } fd_set;
      |     ^~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:21:33: error: conflicting types for ‘dev_t’; have ‘__kernel_dev_t’ {aka ‘unsigned int’}
   21 | typedef __kernel_dev_t          dev_t;
      |                                 ^~~~~
In file included from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/sys/types.h:59:17: note: previous declaration of ‘dev_t’ with type ‘dev_t’ {aka ‘long unsigned int’}
   59 | typedef __dev_t dev_t;
      |                 ^~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:25:33: error: conflicting types for ‘nlink_t’; have ‘u32’ {aka ‘unsigned int’}
   25 | typedef u32                     nlink_t;
      |                                 ^~~~~~~
In file included from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/sys/types.h:74:19: note: previous declaration of ‘nlink_t’ with type ‘nlink_t’ {aka ‘long unsigned int’}
   74 | typedef __nlink_t nlink_t;
      |                   ^~~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:31:33: error: conflicting types for ‘timer_t’; have ‘__kernel_timer_t’ {aka ‘int’}
   31 | typedef __kernel_timer_t        timer_t;
      |                                 ^~~~~~~
In file included from /usr/include/sys/types.h:130,
                 from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/bits/types/timer_t.h:7:19: note: previous declaration of ‘timer_t’ with type ‘timer_t’ {aka ‘void *’}
    7 | typedef __timer_t timer_t;
      |                   ^~~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:52:33: error: conflicting types for ‘loff_t’; have ‘__kernel_loff_t’ {aka ‘long long int’}
   52 | typedef __kernel_loff_t         loff_t;
      |                                 ^~~~~~
In file included from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/sys/types.h:42:18: note: previous declaration of ‘loff_t’ with type ‘loff_t’ {aka ‘long int’}
   42 | typedef __loff_t loff_t;
      |                  ^~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:53:9: error: unknown type name ‘__kernel_uoff_t’
   53 | typedef __kernel_uoff_t         uoff_t;
      |         ^~~~~~~~~~~~~~~
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:115:33: error: conflicting types for ‘uint64_t’; have ‘u64’ {aka ‘long long unsigned int’}
  115 | typedef u64                     uint64_t;
      |                                 ^~~~~~~~
In file included from /usr/include/stdint.h:37,
                 from /usr/lib/gcc/x86_64-redhat-linux/11/include/stdint.h:9,
                 from /usr/include/libelf.h:32,
                 from main.c:68:
/usr/include/bits/stdint-uintn.h:27:20: note: previous declaration of ‘uint64_t’ with type ‘uint64_t’ {aka ‘long unsigned int’}
   27 | typedef __uint64_t uint64_t;
      |                    ^~~~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:116:33: error: conflicting types for ‘u_int64_t’; have ‘u64’ {aka ‘long long unsigned int’}
  116 | typedef u64                     u_int64_t;
      |                                 ^~~~~~~~~
In file included from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/sys/types.h:161:20: note: previous declaration of ‘u_int64_t’ with type ‘u_int64_t’ {aka ‘long unsigned int’}
  161 | typedef __uint64_t u_int64_t;
      |                    ^~~~~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:117:33: error: conflicting types for ‘int64_t’; have ‘s64’ {aka ‘long long int’}
  117 | typedef s64                     int64_t;
      |                                 ^~~~~~~
In file included from /usr/include/sys/types.h:155,
                 from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/bits/stdint-intn.h:27:19: note: previous declaration of ‘int64_t’ with type ‘int64_t’ {aka ‘long int’}
   27 | typedef __int64_t int64_t;
      |                   ^~~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:138:13: error: conflicting types for ‘blkcnt_t’; have ‘u64’ {aka ‘long long unsigned int’}
  138 | typedef u64 blkcnt_t;
      |             ^~~~~~~~
In file included from /usr/include/stdlib.h:394,
                 from main.c:67:
/usr/include/sys/types.h:192:20: note: previous declaration of ‘blkcnt_t’ with type ‘blkcnt_t’ {aka ‘long int’}
  192 | typedef __blkcnt_t blkcnt_t;     /* Type to count number of disk blocks.  */
      |                    ^~~~~~~~
In file included from /home/isolodrai/workspace/prog-aux/linux/include/uapi/linux/stat.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:7,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/linux/types.h:266:34: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘*’ token
  266 |         struct task_struct __rcu *task;
      |                                  ^
In file included from /home/isolodrai/workspace/prog-aux/linux/include/linux/cache.h:6,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/time.h:5,
                 from /home/isolodrai/workspace/prog-aux/linux/include/linux/stat.h:19,
                 from main.c:70:
/home/isolodrai/workspace/prog-aux/linux/include/vdso/cache.h:5:10: fatal error: asm/cache.h: No such file or directory
    5 | #include <asm/cache.h>
      |          ^~~~~~~~~~~~~
compilation terminated.
make[1]: *** [/home/isolodrai/workspace/prog-aux/linux/tools/build/Makefile.build:86: /home/isolodrai/workspace/prog-aux/linux/tools/bpf/resolve_btfids/main.o] Error 1
make: *** [Makefile:81: /home/isolodrai/workspace/prog-aux/linux/tools/bpf/resolve_btfids//resolve_btfids-in.o] Error 2


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