* [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC @ 2022-07-13 22:25 Indu Bhagat 2022-07-13 23:52 ` sdf 2022-07-14 6:00 ` Andrii Nakryiko 0 siblings, 2 replies; 5+ messages in thread From: Indu Bhagat @ 2022-07-13 22:25 UTC (permalink / raw) To: bpf; +Cc: yhs, Indu Bhagat The vlen bits in the BTF type of kind BTF_KIND_FUNC are used to convey the linkage information for functions. Signed-off-by: Indu Bhagat <indu.bhagat@oracle.com> --- Documentation/bpf/btf.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst index f49aeef62d0c..b3a9d5ac882c 100644 --- a/Documentation/bpf/btf.rst +++ b/Documentation/bpf/btf.rst @@ -369,7 +369,7 @@ No additional type data follow ``btf_type``. * ``name_off``: offset to a valid C identifier * ``info.kind_flag``: 0 * ``info.kind``: BTF_KIND_FUNC - * ``info.vlen``: 0 + * ``info.vlen``: linkage information (static=0, global=1) * ``type``: a BTF_KIND_FUNC_PROTO type No additional type data follow ``btf_type``. -- 2.31.1 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC 2022-07-13 22:25 [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC Indu Bhagat @ 2022-07-13 23:52 ` sdf 2022-07-14 6:00 ` Andrii Nakryiko 1 sibling, 0 replies; 5+ messages in thread From: sdf @ 2022-07-13 23:52 UTC (permalink / raw) To: Indu Bhagat; +Cc: bpf, yhs On 07/13, Indu Bhagat wrote: > The vlen bits in the BTF type of kind BTF_KIND_FUNC are used to convey the > linkage information for functions. > Signed-off-by: Indu Bhagat <indu.bhagat@oracle.com> Reviewed-by: Stanislav Fomichev <sdf@google.com> Judging by: static inline u16 btf_func_linkage(const struct btf_type *t) { return BTF_INFO_VLEN(t->info); } > --- > Documentation/bpf/btf.rst | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst > index f49aeef62d0c..b3a9d5ac882c 100644 > --- a/Documentation/bpf/btf.rst > +++ b/Documentation/bpf/btf.rst > @@ -369,7 +369,7 @@ No additional type data follow ``btf_type``. > * ``name_off``: offset to a valid C identifier > * ``info.kind_flag``: 0 > * ``info.kind``: BTF_KIND_FUNC > - * ``info.vlen``: 0 > + * ``info.vlen``: linkage information (static=0, global=1) > * ``type``: a BTF_KIND_FUNC_PROTO type > No additional type data follow ``btf_type``. > -- > 2.31.1 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC 2022-07-13 22:25 [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC Indu Bhagat 2022-07-13 23:52 ` sdf @ 2022-07-14 6:00 ` Andrii Nakryiko 2022-07-14 6:42 ` Yonghong Song 1 sibling, 1 reply; 5+ messages in thread From: Andrii Nakryiko @ 2022-07-14 6:00 UTC (permalink / raw) To: Indu Bhagat; +Cc: bpf, Yonghong Song On Wed, Jul 13, 2022 at 3:37 PM Indu Bhagat <indu.bhagat@oracle.com> wrote: > > The vlen bits in the BTF type of kind BTF_KIND_FUNC are used to convey the > linkage information for functions. > > Signed-off-by: Indu Bhagat <indu.bhagat@oracle.com> > --- > Documentation/bpf/btf.rst | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst > index f49aeef62d0c..b3a9d5ac882c 100644 > --- a/Documentation/bpf/btf.rst > +++ b/Documentation/bpf/btf.rst > @@ -369,7 +369,7 @@ No additional type data follow ``btf_type``. > * ``name_off``: offset to a valid C identifier > * ``info.kind_flag``: 0 > * ``info.kind``: BTF_KIND_FUNC > - * ``info.vlen``: 0 > + * ``info.vlen``: linkage information (static=0, global=1) there is also extern=2, but I think we should just refer to enum btf_func_linkage, defined in UAPI (include/uapi/linux/btf.h) ? > * ``type``: a BTF_KIND_FUNC_PROTO type > > No additional type data follow ``btf_type``. > -- > 2.31.1 > ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC 2022-07-14 6:00 ` Andrii Nakryiko @ 2022-07-14 6:42 ` Yonghong Song 2022-07-14 7:10 ` Andrii Nakryiko 0 siblings, 1 reply; 5+ messages in thread From: Yonghong Song @ 2022-07-14 6:42 UTC (permalink / raw) To: Andrii Nakryiko, Indu Bhagat; +Cc: bpf On 7/13/22 11:00 PM, Andrii Nakryiko wrote: > On Wed, Jul 13, 2022 at 3:37 PM Indu Bhagat <indu.bhagat@oracle.com> wrote: >> >> The vlen bits in the BTF type of kind BTF_KIND_FUNC are used to convey the >> linkage information for functions. >> >> Signed-off-by: Indu Bhagat <indu.bhagat@oracle.com> >> --- >> Documentation/bpf/btf.rst | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst >> index f49aeef62d0c..b3a9d5ac882c 100644 >> --- a/Documentation/bpf/btf.rst >> +++ b/Documentation/bpf/btf.rst >> @@ -369,7 +369,7 @@ No additional type data follow ``btf_type``. >> * ``name_off``: offset to a valid C identifier >> * ``info.kind_flag``: 0 >> * ``info.kind``: BTF_KIND_FUNC >> - * ``info.vlen``: 0 >> + * ``info.vlen``: linkage information (static=0, global=1) > > there is also extern=2, but I think we should just refer to enum > btf_func_linkage, defined in UAPI (include/uapi/linux/btf.h) ? Currently kernel rejects extern=2. In kernel btf.c, we have if (btf_type_vlen(t) > BTF_FUNC_GLOBAL) { btf_verifier_log_type(env, t, "Invalid func linkage"); return -EINVAL; } and extern=2 will cause btf loading failure. The BTF_FUNC_EXTERN is generated when you call an extern *global* function. I suspect that during static linking, all these extern globals should become true global/static functions and not extern func's any more so kernel is okay. So looks like it is worthwhile to mention that BTF_KIND_FUNC supports all three modes as specified in enum btf_func_linkage. But only static/global is supported in the kernel. > >> * ``type``: a BTF_KIND_FUNC_PROTO type >> >> No additional type data follow ``btf_type``. >> -- >> 2.31.1 >> ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC 2022-07-14 6:42 ` Yonghong Song @ 2022-07-14 7:10 ` Andrii Nakryiko 0 siblings, 0 replies; 5+ messages in thread From: Andrii Nakryiko @ 2022-07-14 7:10 UTC (permalink / raw) To: Yonghong Song; +Cc: Indu Bhagat, bpf On Wed, Jul 13, 2022 at 11:42 PM Yonghong Song <yhs@fb.com> wrote: > > > > On 7/13/22 11:00 PM, Andrii Nakryiko wrote: > > On Wed, Jul 13, 2022 at 3:37 PM Indu Bhagat <indu.bhagat@oracle.com> wrote: > >> > >> The vlen bits in the BTF type of kind BTF_KIND_FUNC are used to convey the > >> linkage information for functions. > >> > >> Signed-off-by: Indu Bhagat <indu.bhagat@oracle.com> > >> --- > >> Documentation/bpf/btf.rst | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst > >> index f49aeef62d0c..b3a9d5ac882c 100644 > >> --- a/Documentation/bpf/btf.rst > >> +++ b/Documentation/bpf/btf.rst > >> @@ -369,7 +369,7 @@ No additional type data follow ``btf_type``. > >> * ``name_off``: offset to a valid C identifier > >> * ``info.kind_flag``: 0 > >> * ``info.kind``: BTF_KIND_FUNC > >> - * ``info.vlen``: 0 > >> + * ``info.vlen``: linkage information (static=0, global=1) > > > > there is also extern=2, but I think we should just refer to enum > > btf_func_linkage, defined in UAPI (include/uapi/linux/btf.h) ? > > Currently kernel rejects extern=2. In kernel btf.c, we have > > if (btf_type_vlen(t) > BTF_FUNC_GLOBAL) { > btf_verifier_log_type(env, t, "Invalid func linkage"); > return -EINVAL; > } > > and extern=2 will cause btf loading failure. > > The BTF_FUNC_EXTERN is generated when you call an extern *global* > function. I suspect that during static linking, all these > extern globals should become true global/static functions and > not extern func's any more so kernel is okay. > > So looks like it is worthwhile to mention that BTF_KIND_FUNC > supports all three modes as specified in enum btf_func_linkage. > But only static/global is supported in the kernel. > Exactly. This is specification of BTF format (for clang and gcc to agree upon, for example), while kernel BTF verifier puts extra conditions on top of BTF format itself (as required by C and kernel semantics). So it makes sense to document all possibilities and extra kernel checks. > > > >> * ``type``: a BTF_KIND_FUNC_PROTO type > >> > >> No additional type data follow ``btf_type``. > >> -- > >> 2.31.1 > >> ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-07-14 7:10 UTC | newest] Thread overview: 5+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2022-07-13 22:25 [PATCH bpf-next] docs/bpf: Update documentation for BTF_KIND_FUNC Indu Bhagat 2022-07-13 23:52 ` sdf 2022-07-14 6:00 ` Andrii Nakryiko 2022-07-14 6:42 ` Yonghong Song 2022-07-14 7:10 ` Andrii Nakryiko
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