[PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc prototypes from BTF

[PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc prototypes from BTF

[Daniel Xu]

This patchset enables dumping kfunc prototypes from bpftool. This is
useful b/c with this patchset, end users will no longer have to manually
define kfunc prototypes. For the kernel tree, this also means we can
drop kfunc prototypes from:

        tools/testing/selftests/bpf/bpf_kfuncs.h
        tools/testing/selftests/bpf/bpf_experimental.h

Example usage:

        $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux

        $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
        extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
        extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
        extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;

Note that this patchset is only effective after the enabling pahole [0]
change is merged and the resulting feature enabled with
--btf_features=decl_tag_kfuncs.

[0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/

=== Changelog ===

From v1:
* Add __weak annotation
* Use btf_dump for kfunc prototypes
* Update kernel bpf_rdonly_cast() signature

Daniel Xu (2):
  bpf: Have bpf_rdonly_cast() take a const pointer
  bpftool: Support dumping kfunc prototypes from BTF

 kernel/bpf/helpers.c    |  4 ++--
 tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)

-- 
2.42.1

[PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const pointer

[Daniel Xu]

Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
exporting a const arg version of bpf_rdonly_cast(). This causes the
following conflicting type error when generating kfunc prototypes from
BTF:

In file included from skeleton/pid_iter.bpf.c:5:
/home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
             ^
./vmlinux.h:135625:14: note: previous declaration is here
extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;

This is b/c the kernel defines bpf_rdonly_cast() with non-const arg.
Since const arg is more permissive and thus backwards compatible, we
change the kernel definition as well to avoid conflicting type errors.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 kernel/bpf/helpers.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 4db1c658254c..3503949b4c1b 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2484,9 +2484,9 @@ __bpf_kfunc void *bpf_cast_to_kern_ctx(void *obj)
 	return obj;
 }
 
-__bpf_kfunc void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k)
+__bpf_kfunc void *bpf_rdonly_cast(const void *obj__ign, u32 btf_id__k)
 {
-	return obj__ign;
+	return (void *)obj__ign;
 }
 
 __bpf_kfunc void bpf_rcu_read_lock(void)
-- 
2.42.1

Re: [PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const pointer

[Yonghong Song]

On 2/4/24 1:06 PM, Daniel Xu wrote:
> Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
> exporting a const arg version of bpf_rdonly_cast(). This causes the
> following conflicting type error when generating kfunc prototypes from
> BTF:
>
> In file included from skeleton/pid_iter.bpf.c:5:
> /home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
> extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
>               ^
> ./vmlinux.h:135625:14: note: previous declaration is here
> extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;
>
> This is b/c the kernel defines bpf_rdonly_cast() with non-const arg.
> Since const arg is more permissive and thus backwards compatible, we
> change the kernel definition as well to avoid conflicting type errors.
>
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>

Acked-by: Yonghong Song <yonghong.song@linux.dev>

Re: [PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const pointer

[Jiri Olsa]

On Sun, Feb 04, 2024 at 02:06:34PM -0700, Daniel Xu wrote:
> Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
> exporting a const arg version of bpf_rdonly_cast(). This causes the
> following conflicting type error when generating kfunc prototypes from
> BTF:
> 
> In file included from skeleton/pid_iter.bpf.c:5:
> /home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
> extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
>              ^
> ./vmlinux.h:135625:14: note: previous declaration is here
> extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;

hi,
I'm hiting more of these when compiling bpf selftests (attached),
it looks like some kfuncs declarations in bpf_kfuncs.h might be in conflict

jirka


---
  CLNG-BPF [test_maps] connect_unix_prog.bpf.o
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:11:12: error: conflicting types for 'bpf_dynptr_from_skb'
extern int bpf_dynptr_from_skb(struct __sk_buff *skb, __u64 flags,
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164853:12: note: previous declaration is here
extern int bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags, struct bpf_dynptr_kern *ptr__uninit) __weak __ksym;
           ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:19:12: error: conflicting types for 'bpf_dynptr_from_xdp'
extern int bpf_dynptr_from_xdp(struct xdp_md *xdp, __u64 flags,
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164855:12: note: previous declaration is here
extern int bpf_dynptr_from_xdp(struct xdp_buff *xdp, u64 flags, struct bpf_dynptr_kern *ptr__uninit) __weak __ksym;
           ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:28:14: error: conflicting types for 'bpf_dynptr_slice'
extern void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, __u32 offset,
             ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164747:14: note: previous declaration is here
extern void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset, void *buffer__opt, u32 buffer__szk) __weak __ksym;
             ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:37:14: error: conflicting types for 'bpf_dynptr_slice_rdwr'
extern void *bpf_dynptr_slice_rdwr(const struct bpf_dynptr *ptr, __u32 offset,
             ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164749:14: note: previous declaration is here
extern void *bpf_dynptr_slice_rdwr(const struct bpf_dynptr_kern *ptr, u32 offset, void *buffer__opt, u32 buffer__szk) __weak __ksym;
             ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:40:12: error: conflicting types for 'bpf_dynptr_adjust'
extern int bpf_dynptr_adjust(const struct bpf_dynptr *ptr, __u32 start, __u32 end) __ksym __weak;
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164781:12: note: previous declaration is here
extern int bpf_dynptr_adjust(struct bpf_dynptr_kern *ptr, u32 start, u32 end) __weak __ksym;
           ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:41:13: error: conflicting types for 'bpf_dynptr_is_null'
extern bool bpf_dynptr_is_null(const struct bpf_dynptr *ptr) __ksym __weak;
            ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164783:13: note: previous declaration is here
extern bool bpf_dynptr_is_null(struct bpf_dynptr_kern *ptr) __weak __ksym;
            ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:42:13: error: conflicting types for 'bpf_dynptr_is_rdonly'
extern bool bpf_dynptr_is_rdonly(const struct bpf_dynptr *ptr) __ksym __weak;
            ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164785:13: note: previous declaration is here
extern bool bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr) __weak __ksym;
            ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:43:14: error: conflicting types for 'bpf_dynptr_size'
extern __u32 bpf_dynptr_size(const struct bpf_dynptr *ptr) __ksym __weak;
             ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164787:14: note: previous declaration is here
extern __u32 bpf_dynptr_size(const struct bpf_dynptr_kern *ptr) __weak __ksym;
             ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:44:12: error: conflicting types for 'bpf_dynptr_clone'
extern int bpf_dynptr_clone(const struct bpf_dynptr *ptr, struct bpf_dynptr *clone__init) __ksym __weak;
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164789:12: note: previous declaration is here
extern int bpf_dynptr_clone(struct bpf_dynptr_kern *ptr, struct bpf_dynptr_kern *clone__uninit) __weak __ksym;
           ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:61:12: error: conflicting types for 'bpf_sk_assign_tcp_reqsk'
extern int bpf_sk_assign_tcp_reqsk(struct __sk_buff *skb, struct sock *sk,
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164859:12: note: previous declaration is here
extern int bpf_sk_assign_tcp_reqsk(struct sk_buff *skb, struct sock *sk, struct bpf_tcp_req_attrs *attrs, int attrs__sz) __weak __ksym;
           ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:68:12: error: conflicting types for 'bpf_get_file_xattr'
extern int bpf_get_file_xattr(struct file *file, const char *name,
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164691:12: note: previous declaration is here
extern int bpf_get_file_xattr(struct file *file, const char *name__str, struct bpf_dynptr_kern *value_ptr) __weak __ksym;
           ^
In file included from progs/connect_unix_prog.c:9:
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/bpf_kfuncs.h:75:12: error: conflicting types for 'bpf_verify_pkcs7_signature'
extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
           ^
/home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/tools/include/vmlinux.h:164689:12: note: previous declaration is here
extern int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr, struct bpf_dynptr_kern *sig_ptr, struct bpf_key *trusted_keyring) __weak __ksym;
           ^
12 errors generated.
make: *** [Makefile:642: /home/jolsa/kernel/linux-qemu/tools/testing/selftests/bpf/connect_unix_prog.bpf.o] Error 1

Re: [PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const pointer

[Daniel Xu]

Hi Jiri,

On Tue, Feb 06, 2024 at 02:42:22PM +0100, Jiri Olsa wrote:
> On Sun, Feb 04, 2024 at 02:06:34PM -0700, Daniel Xu wrote:
> > Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
> > exporting a const arg version of bpf_rdonly_cast(). This causes the
> > following conflicting type error when generating kfunc prototypes from
> > BTF:
> > 
> > In file included from skeleton/pid_iter.bpf.c:5:
> > /home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
> > extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
> >              ^
> > ./vmlinux.h:135625:14: note: previous declaration is here
> > extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;
> 
> hi,
> I'm hiting more of these when compiling bpf selftests (attached),
> it looks like some kfuncs declarations in bpf_kfuncs.h might be in conflict

Yep, I was actually going to put that as an office hours topic on how we
want to handle that for selftests. Marking kfuncs in bpf_kfuncs.h and
bpf_experimental.h as __weak is an option. ifdef is another option.
Final option I can think of is bumping required pahole version up and
simply deleting all the kfunc definitions.

But given that pahole changes come with the feature flag, I don't see
this as a pressing issue. So I was planning on getting to that after
current outstanding patchsets (just so there's less stuff for me to
juggle).

[...]

Thanks,
Daniel

Re: [PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const pointer

[Jiri Olsa]

On Tue, Feb 06, 2024 at 08:44:18AM -0700, Daniel Xu wrote:
> Hi Jiri,
> 
> On Tue, Feb 06, 2024 at 02:42:22PM +0100, Jiri Olsa wrote:
> > On Sun, Feb 04, 2024 at 02:06:34PM -0700, Daniel Xu wrote:
> > > Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
> > > exporting a const arg version of bpf_rdonly_cast(). This causes the
> > > following conflicting type error when generating kfunc prototypes from
> > > BTF:
> > > 
> > > In file included from skeleton/pid_iter.bpf.c:5:
> > > /home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
> > > extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
> > >              ^
> > > ./vmlinux.h:135625:14: note: previous declaration is here
> > > extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;
> > 
> > hi,
> > I'm hiting more of these when compiling bpf selftests (attached),
> > it looks like some kfuncs declarations in bpf_kfuncs.h might be in conflict
> 
> Yep, I was actually going to put that as an office hours topic on how we
> want to handle that for selftests. Marking kfuncs in bpf_kfuncs.h and
> bpf_experimental.h as __weak is an option. ifdef is another option.
> Final option I can think of is bumping required pahole version up and
> simply deleting all the kfunc definitions.
> 
> But given that pahole changes come with the feature flag, I don't see
> this as a pressing issue. So I was planning on getting to that after
> current outstanding patchsets (just so there's less stuff for me to
> juggle).

ok, I guess if the fix goes in together with the scripts/Makefile.btf
change then we're fine

jirka

Re: [PATCH bpf-next v2 1/2] bpf: Have bpf_rdonly_cast() take a const pointer

[Andrii Nakryiko]

On Tue, Feb 6, 2024 at 7:44 AM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> Hi Jiri,
>
> On Tue, Feb 06, 2024 at 02:42:22PM +0100, Jiri Olsa wrote:
> > On Sun, Feb 04, 2024 at 02:06:34PM -0700, Daniel Xu wrote:
> > > Since 20d59ee55172 ("libbpf: add bpf_core_cast() macro"), libbpf is now
> > > exporting a const arg version of bpf_rdonly_cast(). This causes the
> > > following conflicting type error when generating kfunc prototypes from
> > > BTF:
> > >
> > > In file included from skeleton/pid_iter.bpf.c:5:
> > > /home/dxu/dev/linux/tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_core_read.h:297:14: error: conflicting types for 'bpf_rdonly_cast'
> > > extern void *bpf_rdonly_cast(const void *obj__ign, __u32 btf_id__k) __ksym __weak;
> > >              ^
> > > ./vmlinux.h:135625:14: note: previous declaration is here
> > > extern void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k) __weak __ksym;
> >
> > hi,
> > I'm hiting more of these when compiling bpf selftests (attached),
> > it looks like some kfuncs declarations in bpf_kfuncs.h might be in conflict
>
> Yep, I was actually going to put that as an office hours topic on how we
> want to handle that for selftests. Marking kfuncs in bpf_kfuncs.h and
> bpf_experimental.h as __weak is an option. ifdef is another option.
> Final option I can think of is bumping required pahole version up and
> simply deleting all the kfunc definitions.

I think we should mark all kfuncs in selftests as __weak. And then
audit all of them and add consts where it makes sense and make sure
that all definitions are compatible between vmlinux.h and manual
declarations. I'd rather avoid #ifdef'ing anything, it should work as
is.


>
> But given that pahole changes come with the feature flag, I don't see
> this as a pressing issue. So I was planning on getting to that after
> current outstanding patchsets (just so there's less stuff for me to
> juggle).
>
> [...]
>
> Thanks,
> Daniel

[PATCH bpf-next v2 2/2] bpftool: Support dumping kfunc prototypes from BTF

[Daniel Xu]

This patch enables dumping kfunc prototypes from bpftool. This is useful
b/c with this patch, end users will no longer have to manually define
kfunc prototypes. For the kernel tree, this also means we can drop
kfunc prototypes from:

        tools/testing/selftests/bpf/bpf_kfuncs.h
        tools/testing/selftests/bpf/bpf_experimental.h

Example usage:

        $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux

        $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
        extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
        extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
        extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;

Note that this patch is only effective after the enabling pahole [0]
change is merged and the resulting feature enabled with
--btf_features=decl_tag_kfuncs.

[0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 91fcb75babe3..0fd78a476286 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -20,6 +20,8 @@
 #include "json_writer.h"
 #include "main.h"
 
+#define KFUNC_DECL_TAG		"bpf_kfunc"
+
 static const char * const btf_kind_str[NR_BTF_KINDS] = {
 	[BTF_KIND_UNKN]		= "UNKNOWN",
 	[BTF_KIND_INT]		= "INT",
@@ -454,6 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
 	return 0;
 }
 
+static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
+{
+	DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
+	int cnt = btf__type_cnt(btf);
+	int i;
+
+	for (i = 1; i < cnt; i++) {
+		const struct btf_type *t = btf__type_by_id(btf, i);
+		const struct btf_type *kft;
+		const char *name;
+		int err;
+
+		if (!btf_is_decl_tag(t))
+			continue;
+
+		name = btf__name_by_offset(btf, t->name_off);
+		if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
+			continue;
+
+		printf("extern ");
+
+		kft = btf__type_by_id(btf, t->type);
+		opts.field_name = btf__name_by_offset(btf, kft->name_off);
+		err = btf_dump__emit_type_decl(d, kft->type, &opts);
+		if (err)
+			return err;
+
+		printf(" __weak __ksym;\n\n");
+	}
+
+	return 0;
+}
+
 static void __printf(2, 0) btf_dump_printf(void *ctx,
 					   const char *fmt, va_list args)
 {
@@ -476,6 +511,12 @@ static int dump_btf_c(const struct btf *btf,
 	printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
 	printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
 	printf("#endif\n\n");
+	printf("#ifndef __ksym\n");
+	printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
+	printf("#endif\n\n");
+	printf("#ifndef __weak\n");
+	printf("#define __weak __attribute__((weak))\n");
+	printf("#endif\n\n");
 
 	if (root_type_cnt) {
 		for (i = 0; i < root_type_cnt; i++) {
@@ -491,6 +532,10 @@ static int dump_btf_c(const struct btf *btf,
 			if (err)
 				goto done;
 		}
+
+		err = dump_btf_kfuncs(d, btf);
+		if (err)
+			goto done;
 	}
 
 	printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
-- 
2.42.1

Re: [PATCH bpf-next v2 2/2] bpftool: Support dumping kfunc prototypes from BTF

[Andrii Nakryiko]

On Sun, Feb 4, 2024 at 1:07 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> This patch enables dumping kfunc prototypes from bpftool. This is useful
> b/c with this patch, end users will no longer have to manually define
> kfunc prototypes. For the kernel tree, this also means we can drop
> kfunc prototypes from:
>
>         tools/testing/selftests/bpf/bpf_kfuncs.h
>         tools/testing/selftests/bpf/bpf_experimental.h
>
> Example usage:
>
>         $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
>
>         $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
>         extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
>         extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
>         extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
>
> Note that this patch is only effective after the enabling pahole [0]
> change is merged and the resulting feature enabled with
> --btf_features=decl_tag_kfuncs.
>
> [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
>
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> ---
>  tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
>
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 91fcb75babe3..0fd78a476286 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -20,6 +20,8 @@
>  #include "json_writer.h"
>  #include "main.h"
>
> +#define KFUNC_DECL_TAG         "bpf_kfunc"
> +
>  static const char * const btf_kind_str[NR_BTF_KINDS] = {
>         [BTF_KIND_UNKN]         = "UNKNOWN",
>         [BTF_KIND_INT]          = "INT",
> @@ -454,6 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
>         return 0;
>  }
>
> +static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
> +{
> +       DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);

nit: use shorter LIBBPF_OPTS, DECLARE_LIBBPF_OPTS is a "deprecated"
macro name I hid, but didn't remove

> +       int cnt = btf__type_cnt(btf);
> +       int i;
> +
> +       for (i = 1; i < cnt; i++) {
> +               const struct btf_type *t = btf__type_by_id(btf, i);
> +               const struct btf_type *kft;
> +               const char *name;
> +               int err;
> +
> +               if (!btf_is_decl_tag(t))
> +                       continue;
> +
> +               name = btf__name_by_offset(btf, t->name_off);
> +               if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
> +                       continue;

should we do a bit more sanity checking here? Check that component_idx
= -1 (entire func) and pointee type is FUNC?

> +
> +               printf("extern ");
> +
> +               kft = btf__type_by_id(btf, t->type);

nit: reuse t?

> +               opts.field_name = btf__name_by_offset(btf, kft->name_off);
> +               err = btf_dump__emit_type_decl(d, kft->type, &opts);
> +               if (err)
> +                       return err;
> +
> +               printf(" __weak __ksym;\n\n");

why extra endline?

though I'd ensure two empty lines before the first kfunc declaration
to visually separate it from other type. Maybe even add a comment like
`/* BPF kfuncs */` or something like that?

> +       }
> +
> +       return 0;
> +}
> +
>  static void __printf(2, 0) btf_dump_printf(void *ctx,
>                                            const char *fmt, va_list args)
>  {
> @@ -476,6 +511,12 @@ static int dump_btf_c(const struct btf *btf,
>         printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
>         printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
>         printf("#endif\n\n");
> +       printf("#ifndef __ksym\n");
> +       printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
> +       printf("#endif\n\n");
> +       printf("#ifndef __weak\n");
> +       printf("#define __weak __attribute__((weak))\n");
> +       printf("#endif\n\n");
>
>         if (root_type_cnt) {
>                 for (i = 0; i < root_type_cnt; i++) {
> @@ -491,6 +532,10 @@ static int dump_btf_c(const struct btf *btf,
>                         if (err)
>                                 goto done;
>                 }
> +
> +               err = dump_btf_kfuncs(d, btf);
> +               if (err)
> +                       goto done;
>         }
>
>         printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> --
> 2.42.1
>

Re: [PATCH bpf-next v2 2/2] bpftool: Support dumping kfunc prototypes from BTF

[Daniel Xu]

Hi Andrii,

On Wed, Feb 07, 2024 at 04:50:15PM -0800, Andrii Nakryiko wrote:
> On Sun, Feb 4, 2024 at 1:07 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
> >
> > This patch enables dumping kfunc prototypes from bpftool. This is useful
> > b/c with this patch, end users will no longer have to manually define
> > kfunc prototypes. For the kernel tree, this also means we can drop
> > kfunc prototypes from:
> >
> >         tools/testing/selftests/bpf/bpf_kfuncs.h
> >         tools/testing/selftests/bpf/bpf_experimental.h
> >
> > Example usage:
> >
> >         $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
> >
> >         $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
> >         extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
> >         extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
> >         extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
> >
> > Note that this patch is only effective after the enabling pahole [0]
> > change is merged and the resulting feature enabled with
> > --btf_features=decl_tag_kfuncs.
> >
> > [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
> >
> > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> > ---
> >  tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 45 insertions(+)
> >
> > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> > index 91fcb75babe3..0fd78a476286 100644
> > --- a/tools/bpf/bpftool/btf.c
> > +++ b/tools/bpf/bpftool/btf.c
> > @@ -20,6 +20,8 @@
> >  #include "json_writer.h"
> >  #include "main.h"
> >
> > +#define KFUNC_DECL_TAG         "bpf_kfunc"
> > +
> >  static const char * const btf_kind_str[NR_BTF_KINDS] = {
> >         [BTF_KIND_UNKN]         = "UNKNOWN",
> >         [BTF_KIND_INT]          = "INT",
> > @@ -454,6 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
> >         return 0;
> >  }
> >
> > +static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
> > +{
> > +       DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
> 
> nit: use shorter LIBBPF_OPTS, DECLARE_LIBBPF_OPTS is a "deprecated"
> macro name I hid, but didn't remove

Ack.

> 
> > +       int cnt = btf__type_cnt(btf);
> > +       int i;
> > +
> > +       for (i = 1; i < cnt; i++) {
> > +               const struct btf_type *t = btf__type_by_id(btf, i);
> > +               const struct btf_type *kft;
> > +               const char *name;
> > +               int err;
> > +
> > +               if (!btf_is_decl_tag(t))
> > +                       continue;
> > +
> > +               name = btf__name_by_offset(btf, t->name_off);
> > +               if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
> > +                       continue;
> 
> should we do a bit more sanity checking here? Check that component_idx
> = -1 (entire func) and pointee type is FUNC?

Makes sense. Will add.

> 
> > +
> > +               printf("extern ");
> > +
> > +               kft = btf__type_by_id(btf, t->type);
> 
> nit: reuse t?
> 
> > +               opts.field_name = btf__name_by_offset(btf, kft->name_off);
> > +               err = btf_dump__emit_type_decl(d, kft->type, &opts);
> > +               if (err)
> > +                       return err;
> > +
> > +               printf(" __weak __ksym;\n\n");
> 
> why extra endline?

Was thinking b/c other entities (structs) are double newline separated
that we should keep it up for kfunc prototypes. No opinion -- I'll
change it.

> 
> though I'd ensure two empty lines before the first kfunc declaration
> to visually separate it from other type. Maybe even add a comment like
> `/* BPF kfuncs */` or something like that?

Ack.

> 
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> >  static void __printf(2, 0) btf_dump_printf(void *ctx,
> >                                            const char *fmt, va_list args)
> >  {
> > @@ -476,6 +511,12 @@ static int dump_btf_c(const struct btf *btf,
> >         printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> >         printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
> >         printf("#endif\n\n");
> > +       printf("#ifndef __ksym\n");
> > +       printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
> > +       printf("#endif\n\n");
> > +       printf("#ifndef __weak\n");
> > +       printf("#define __weak __attribute__((weak))\n");
> > +       printf("#endif\n\n");
> >
> >         if (root_type_cnt) {
> >                 for (i = 0; i < root_type_cnt; i++) {
> > @@ -491,6 +532,10 @@ static int dump_btf_c(const struct btf *btf,
> >                         if (err)
> >                                 goto done;
> >                 }
> > +
> > +               err = dump_btf_kfuncs(d, btf);
> > +               if (err)
> > +                       goto done;
> >         }
> >
> >         printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> > --
> > 2.42.1
> >

I'll send the next rev after the pahole changes get merged.

Thanks,
Daniel

Re: [PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc prototypes from BTF

[Andrii Nakryiko]

On Sun, Feb 4, 2024 at 1:06 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> This patchset enables dumping kfunc prototypes from bpftool. This is
> useful b/c with this patchset, end users will no longer have to manually
> define kfunc prototypes. For the kernel tree, this also means we can
> drop kfunc prototypes from:
>
>         tools/testing/selftests/bpf/bpf_kfuncs.h
>         tools/testing/selftests/bpf/bpf_experimental.h
>
> Example usage:
>
>         $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
>
>         $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
>         extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
>         extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
>         extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
>
> Note that this patchset is only effective after the enabling pahole [0]
> change is merged and the resulting feature enabled with
> --btf_features=decl_tag_kfuncs.
>
> [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
>
> === Changelog ===
>
> From v1:
> * Add __weak annotation
> * Use btf_dump for kfunc prototypes
> * Update kernel bpf_rdonly_cast() signature
>
> Daniel Xu (2):
>   bpf: Have bpf_rdonly_cast() take a const pointer
>   bpftool: Support dumping kfunc prototypes from BTF

I've applied patch #1 as it's a good change regardless. Please send v2
for patch #2.

>
>  kernel/bpf/helpers.c    |  4 ++--
>  tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+), 2 deletions(-)
>
> --
> 2.42.1
>

Re: [PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc prototypes from BTF

[Daniel Xu]

On Tue, Feb 13, 2024 at 11:09:29AM -0800, Andrii Nakryiko wrote:
> On Sun, Feb 4, 2024 at 1:06 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
> >
> > This patchset enables dumping kfunc prototypes from bpftool. This is
> > useful b/c with this patchset, end users will no longer have to manually
> > define kfunc prototypes. For the kernel tree, this also means we can
> > drop kfunc prototypes from:
> >
> >         tools/testing/selftests/bpf/bpf_kfuncs.h
> >         tools/testing/selftests/bpf/bpf_experimental.h
> >
> > Example usage:
> >
> >         $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
> >
> >         $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
> >         extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
> >         extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
> >         extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
> >
> > Note that this patchset is only effective after the enabling pahole [0]
> > change is merged and the resulting feature enabled with
> > --btf_features=decl_tag_kfuncs.
> >
> > [0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
> >
> > === Changelog ===
> >
> > From v1:
> > * Add __weak annotation
> > * Use btf_dump for kfunc prototypes
> > * Update kernel bpf_rdonly_cast() signature
> >
> > Daniel Xu (2):
> >   bpf: Have bpf_rdonly_cast() take a const pointer
> >   bpftool: Support dumping kfunc prototypes from BTF
> 
> I've applied patch #1 as it's a good change regardless. Please send v2
> for patch #2.

Ack. Been a bit busy recently - will probably have time to work on this
again next weekend.