Commit 391145ba authored by Dave Marchevsky's avatar Dave Marchevsky Committed by Alexei Starovoitov
Browse files

bpf: Add __bpf_kfunc_{start,end}_defs macros 

BPF kfuncs are meant to be called from BPF programs. Accordingly, most
kfuncs are not called from anywhere in the kernel, which the
-Wmissing-prototypes warning is unhappy about. We've peppered
__diag_ignore_all("-Wmissing-prototypes", ... everywhere kfuncs are
defined in the codebase to suppress this warning.

This patch adds two macros meant to bound one or many kfunc definitions.
All existing kfunc definitions which use these __diag calls to suppress
-Wmissing-prototypes are migrated to use the newly-introduced macros.
A new __diag_ignore_all - for "-Wmissing-declarations" - is added to the
__bpf_kfunc_start_defs macro based on feedback from Andrii on an earlier
version of this patch [0] and another recent mailing list thread [1].

In the future we might need to ignore different warnings or do other
kfunc-specific things. This change will make it easier to make such
modifications for all kfunc defs.

  [0]: https://lore.kernel.org/bpf/CAEf4BzaE5dRWtK6RPLnjTW-MW9sx9K3Fn6uwqCTChK2Dcb1Xig@mail.gmail.com/
  [1]: https://lore.kernel.org/bpf/ZT+2qCc%2FaXep0%2FLf@krava/



Signed-off-by: default avatarDave Marchevsky <davemarchevsky@fb.com>
Suggested-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Acked-by: default avatarYafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20231031215625.2343848-1-davemarchevsky@fb.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent cd60f410

Documentation/bpf/kfuncs.rst

+2 −4
Original line number Diff line number Diff line
@@ -37,16 +37,14 @@ prototype in a header for the wrapper kfunc. 
An example is given below::



        /* Disables missing prototype warnings */

        __diag_push();

        __diag_ignore_all("-Wmissing-prototypes",

                          "Global kfuncs as their definitions will be in BTF");

        __bpf_kfunc_start_defs();



        __bpf_kfunc struct task_struct *bpf_find_get_task_by_vpid(pid_t nr)

        {

                return find_get_task_by_vpid(nr);

        }



        __diag_pop();

        __bpf_kfunc_end_defs();



A wrapper kfunc is often needed when we need to annotate parameters of the

kfunc. Otherwise one may directly make the kfunc visible to the BPF program by

include/linux/btf.h

+9 −0
Original line number Diff line number Diff line
@@ -84,6 +84,15 @@ 
 */

#define __bpf_kfunc __used noinline



#define __bpf_kfunc_start_defs()					       \

	__diag_push();							       \

	__diag_ignore_all("-Wmissing-declarations",			       \

			  "Global kfuncs as their definitions will be in BTF");\

	__diag_ignore_all("-Wmissing-prototypes",			       \

			  "Global kfuncs as their definitions will be in BTF")



#define __bpf_kfunc_end_defs() __diag_pop()



/*

 * Return the name of the passed struct, if exists, or halt the build if for

 * example the structure gets renamed. In this way, developers have to revisit

kernel/bpf/bpf_iter.c

+2 −4
Original line number Diff line number Diff line
@@ -782,9 +782,7 @@ struct bpf_iter_num_kern { 
	int end; /* final value, exclusive */

} __aligned(8);



__diag_push();

__diag_ignore_all("-Wmissing-prototypes",

		  "Global functions as their definitions will be in vmlinux BTF");

__bpf_kfunc_start_defs();



__bpf_kfunc int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end)

{
@@ -843,4 +841,4 @@ __bpf_kfunc void bpf_iter_num_destroy(struct bpf_iter_num *it) 
	s->cur = s->end = 0;

}



__diag_pop();
 
__bpf_kfunc_end_defs();

kernel/bpf/cgroup_iter.c

+2 −4
Original line number Diff line number Diff line
@@ -305,9 +305,7 @@ struct bpf_iter_css_kern { 
	unsigned int flags;

} __attribute__((aligned(8)));



__diag_push();

__diag_ignore_all("-Wmissing-prototypes",

		"Global functions as their definitions will be in vmlinux BTF");

__bpf_kfunc_start_defs();



__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,

		struct cgroup_subsys_state *start, unsigned int flags)
@@ -358,4 +356,4 @@ __bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it) 
{

}



__diag_pop();
 
 No newline at end of file
 
__bpf_kfunc_end_defs();

kernel/bpf/cpumask.c

+2 −4
Original line number Diff line number Diff line
@@ -34,9 +34,7 @@ static bool cpu_valid(u32 cpu) 
	return cpu < nr_cpu_ids;

}



__diag_push();

__diag_ignore_all("-Wmissing-prototypes",

		  "Global kfuncs as their definitions will be in BTF");

__bpf_kfunc_start_defs();



/**

 * bpf_cpumask_create() - Create a mutable BPF cpumask.
@@ -407,7 +405,7 @@ __bpf_kfunc u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1, 
	return cpumask_any_and_distribute(src1, src2);

}



__diag_pop();

__bpf_kfunc_end_defs();



BTF_SET8_START(cpumask_kfunc_btf_ids)

BTF_ID_FLAGS(func, bpf_cpumask_create, KF_ACQUIRE | KF_RET_NULL)