| Message ID | 1605291013-22575-2-git-send-email-alan.maguire@oracle.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | bpf: support module BTF in btf display helpers | expand |
On Fri, Nov 13, 2020 at 10:11 AM Alan Maguire <alan.maguire@oracle.com> wrote: > > bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *" > argument that specifies type information about the type to > be displayed. Augment this information to include a module > name, allowing such display to support module types. > > Signed-off-by: Alan Maguire <alan.maguire@oracle.com> > --- > include/linux/btf.h | 8 ++++++++ > include/uapi/linux/bpf.h | 5 ++++- > kernel/bpf/btf.c | 18 ++++++++++++++++++ > kernel/trace/bpf_trace.c | 42 ++++++++++++++++++++++++++++++++---------- > tools/include/uapi/linux/bpf.h | 5 ++++- > 5 files changed, 66 insertions(+), 12 deletions(-) > > diff --git a/include/linux/btf.h b/include/linux/btf.h > index 2bf6418..d55ca00 100644 > --- a/include/linux/btf.h > +++ b/include/linux/btf.h > @@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo *btf_type_var_secinfo( > const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id); > const char *btf_name_by_offset(const struct btf *btf, u32 offset); > struct btf *btf_parse_vmlinux(void); > +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES > +struct btf *bpf_get_btf_module(const char *name); > +#else > +static inline struct btf *bpf_get_btf_module(const char *name) > +{ > + return ERR_PTR(-ENOTSUPP); > +} > +#endif > struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog); > #else > static inline const struct btf_type *btf_type_by_id(const struct btf *btf, > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 162999b..26978be 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { > * the pointer data is carried out to avoid kernel crashes during > * operation. Smaller types can use string space on the stack; > * larger programs can use map data to store the string > - * representation. > + * representation. Module-specific data structures can be > + * displayed if the module name is supplied. > * > * The string can be subsequently shared with userspace via > * bpf_perf_event_output() or ring buffer interfaces. > @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { > * potentially to specify additional details about the BTF pointer > * (rather than its mode of display) - is included for future use. > * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. > + * A module name can be specified for module-specific data. > */ > struct btf_ptr { > void *ptr; > __u32 type_id; > __u32 flags; /* BTF ptr flags; unused at present. */ > + const char *module; /* optional module name. */ I think module name is a wrong API here, similarly how type name was wrong API for specifying the type (and thus we use type_id here). Using the module's BTF ID seems like a more suitable interface. That's what I'm going to use for all kinds of existing BPF APIs that expect BTF type to attach BPF programs. Right now, we use only type_id and implicitly know that it's in vmlinux BTF. With module BTFs, we now need a pair of BTF object ID + BTF type ID to uniquely identify the type. vmlinux BTF now can be specified in two different ways: either leaving BTF object ID as zero (for simplicity and backwards compatibility) or specifying it's actual BTF obj ID (which pretty much always should be 1, btw). This feels like a natural extension, WDYT? And similar to type_id, no one should expect users to specify these IDs by hand, Clang built-in and libbpf should work together to figure this out for the kernel to use. BTW, with module names there is an extra problem for end users. Some types could be either built-in or built as a module (e.g., XFS data structures). Why would we require BPF users to care which is the case on any given host? It feels right now that we should just extend the existing __builtin_btf_type_id() helper to generate ldimm64 instructions that would encode both BTF type ID and BTF object ID. This would just naturally add transparent module BTF support without BPF programs having to do any changes. But we need to do a bit of thinking and experimentation with Yonghong, haven't gotten around to this yet, you are running a bit ahead of me with module BTFs. :) > }; > > /* [...] > struct btf_ptr { > void *ptr; > __u32 type_id; > __u32 flags; /* BTF ptr flags; unused at present. */ Also, if flags are not used at present, can we repurpose it to just encode btf_obj_id and avoid (at least for now) the backwards compatibility checks based on btf_ptr size? > + const char *module; /* optional module name. */ > }; > > /* > -- > 1.8.3.1 >
On Fri, Nov 13, 2020 at 10:59 PM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Fri, Nov 13, 2020 at 10:11 AM Alan Maguire <alan.maguire@oracle.com> wrote: > > > > bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *" > > argument that specifies type information about the type to > > be displayed. Augment this information to include a module > > name, allowing such display to support module types. > > > > Signed-off-by: Alan Maguire <alan.maguire@oracle.com> > > --- > > include/linux/btf.h | 8 ++++++++ > > include/uapi/linux/bpf.h | 5 ++++- > > kernel/bpf/btf.c | 18 ++++++++++++++++++ > > kernel/trace/bpf_trace.c | 42 ++++++++++++++++++++++++++++++++---------- > > tools/include/uapi/linux/bpf.h | 5 ++++- > > 5 files changed, 66 insertions(+), 12 deletions(-) > > > > diff --git a/include/linux/btf.h b/include/linux/btf.h > > index 2bf6418..d55ca00 100644 > > --- a/include/linux/btf.h > > +++ b/include/linux/btf.h > > @@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo *btf_type_var_secinfo( > > const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id); > > const char *btf_name_by_offset(const struct btf *btf, u32 offset); > > struct btf *btf_parse_vmlinux(void); > > +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES > > +struct btf *bpf_get_btf_module(const char *name); > > +#else > > +static inline struct btf *bpf_get_btf_module(const char *name) > > +{ > > + return ERR_PTR(-ENOTSUPP); > > +} > > +#endif > > struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog); > > #else > > static inline const struct btf_type *btf_type_by_id(const struct btf *btf, > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > index 162999b..26978be 100644 > > --- a/include/uapi/linux/bpf.h > > +++ b/include/uapi/linux/bpf.h > > @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { > > * the pointer data is carried out to avoid kernel crashes during > > * operation. Smaller types can use string space on the stack; > > * larger programs can use map data to store the string > > - * representation. > > + * representation. Module-specific data structures can be > > + * displayed if the module name is supplied. > > * > > * The string can be subsequently shared with userspace via > > * bpf_perf_event_output() or ring buffer interfaces. > > @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { > > * potentially to specify additional details about the BTF pointer > > * (rather than its mode of display) - is included for future use. > > * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. > > + * A module name can be specified for module-specific data. > > */ > > struct btf_ptr { > > void *ptr; > > __u32 type_id; > > __u32 flags; /* BTF ptr flags; unused at present. */ > > + const char *module; /* optional module name. */ > > I think module name is a wrong API here, similarly how type name was > wrong API for specifying the type (and thus we use type_id here). > Using the module's BTF ID seems like a more suitable interface. That's > what I'm going to use for all kinds of existing BPF APIs that expect > BTF type to attach BPF programs. > > Right now, we use only type_id and implicitly know that it's in > vmlinux BTF. With module BTFs, we now need a pair of BTF object ID + > BTF type ID to uniquely identify the type. vmlinux BTF now can be > specified in two different ways: either leaving BTF object ID as zero > (for simplicity and backwards compatibility) or specifying it's actual > BTF obj ID (which pretty much always should be 1, btw). This feels > like a natural extension, WDYT? > > And similar to type_id, no one should expect users to specify these > IDs by hand, Clang built-in and libbpf should work together to figure > this out for the kernel to use. > > BTW, with module names there is an extra problem for end users. Some > types could be either built-in or built as a module (e.g., XFS data > structures). Why would we require BPF users to care which is the case > on any given host? +1. As much as possible libbpf should try to hide the difference between type in a module vs type in the vmlinux, since that difference most of the time is irrelevant from bpf prog pov.
On 11/14/20 8:04 AM, Alexei Starovoitov wrote: > On Fri, Nov 13, 2020 at 10:59 PM Andrii Nakryiko > <andrii.nakryiko@gmail.com> wrote: >> >> On Fri, Nov 13, 2020 at 10:11 AM Alan Maguire <alan.maguire@oracle.com> wrote: >>> >>> bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *" >>> argument that specifies type information about the type to >>> be displayed. Augment this information to include a module >>> name, allowing such display to support module types. >>> >>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com> >>> --- >>> include/linux/btf.h | 8 ++++++++ >>> include/uapi/linux/bpf.h | 5 ++++- >>> kernel/bpf/btf.c | 18 ++++++++++++++++++ >>> kernel/trace/bpf_trace.c | 42 ++++++++++++++++++++++++++++++++---------- >>> tools/include/uapi/linux/bpf.h | 5 ++++- >>> 5 files changed, 66 insertions(+), 12 deletions(-) >>> >>> diff --git a/include/linux/btf.h b/include/linux/btf.h >>> index 2bf6418..d55ca00 100644 >>> --- a/include/linux/btf.h >>> +++ b/include/linux/btf.h >>> @@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo *btf_type_var_secinfo( >>> const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id); >>> const char *btf_name_by_offset(const struct btf *btf, u32 offset); >>> struct btf *btf_parse_vmlinux(void); >>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES >>> +struct btf *bpf_get_btf_module(const char *name); >>> +#else >>> +static inline struct btf *bpf_get_btf_module(const char *name) >>> +{ >>> + return ERR_PTR(-ENOTSUPP); >>> +} >>> +#endif >>> struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog); >>> #else >>> static inline const struct btf_type *btf_type_by_id(const struct btf *btf, >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >>> index 162999b..26978be 100644 >>> --- a/include/uapi/linux/bpf.h >>> +++ b/include/uapi/linux/bpf.h >>> @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { >>> * the pointer data is carried out to avoid kernel crashes during >>> * operation. Smaller types can use string space on the stack; >>> * larger programs can use map data to store the string >>> - * representation. >>> + * representation. Module-specific data structures can be >>> + * displayed if the module name is supplied. >>> * >>> * The string can be subsequently shared with userspace via >>> * bpf_perf_event_output() or ring buffer interfaces. >>> @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { >>> * potentially to specify additional details about the BTF pointer >>> * (rather than its mode of display) - is included for future use. >>> * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. >>> + * A module name can be specified for module-specific data. >>> */ >>> struct btf_ptr { >>> void *ptr; >>> __u32 type_id; >>> __u32 flags; /* BTF ptr flags; unused at present. */ >>> + const char *module; /* optional module name. */ >> >> I think module name is a wrong API here, similarly how type name was >> wrong API for specifying the type (and thus we use type_id here). >> Using the module's BTF ID seems like a more suitable interface. That's >> what I'm going to use for all kinds of existing BPF APIs that expect >> BTF type to attach BPF programs. >> >> Right now, we use only type_id and implicitly know that it's in >> vmlinux BTF. With module BTFs, we now need a pair of BTF object ID + >> BTF type ID to uniquely identify the type. vmlinux BTF now can be >> specified in two different ways: either leaving BTF object ID as zero >> (for simplicity and backwards compatibility) or specifying it's actual >> BTF obj ID (which pretty much always should be 1, btw). This feels >> like a natural extension, WDYT? >> >> And similar to type_id, no one should expect users to specify these >> IDs by hand, Clang built-in and libbpf should work together to figure >> this out for the kernel to use. >> >> BTW, with module names there is an extra problem for end users. Some >> types could be either built-in or built as a module (e.g., XFS data >> structures). Why would we require BPF users to care which is the case >> on any given host? > > +1. > As much as possible libbpf should try to hide the difference between > type in a module vs type in the vmlinux, since that difference most of the > time is irrelevant from bpf prog pov. I just crafted a llvm patch where for __builtin_btf_type_id(), a 64bit value is returned instead of a 32bit value. libbpf can use the lower 32bit as the btf_type_id and upper 32bit as the kernel module btf id. https://reviews.llvm.org/D91489 feel free to experiment with it to see whether it helps.
On Sat, 14 Nov 2020, Yonghong Song wrote: > > > On 11/14/20 8:04 AM, Alexei Starovoitov wrote: > > On Fri, Nov 13, 2020 at 10:59 PM Andrii Nakryiko > > <andrii.nakryiko@gmail.com> wrote: > >> > >> On Fri, Nov 13, 2020 at 10:11 AM Alan Maguire <alan.maguire@oracle.com> > >> wrote: > >>> > >>> bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *" > >>> argument that specifies type information about the type to > >>> be displayed. Augment this information to include a module > >>> name, allowing such display to support module types. > >>> > >>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com> > >>> --- > >>> include/linux/btf.h | 8 ++++++++ > >>> include/uapi/linux/bpf.h | 5 ++++- > >>> kernel/bpf/btf.c | 18 ++++++++++++++++++ > >>> kernel/trace/bpf_trace.c | 42 > >>> ++++++++++++++++++++++++++++++++---------- > >>> tools/include/uapi/linux/bpf.h | 5 ++++- > >>> 5 files changed, 66 insertions(+), 12 deletions(-) > >>> > >>> diff --git a/include/linux/btf.h b/include/linux/btf.h > >>> index 2bf6418..d55ca00 100644 > >>> --- a/include/linux/btf.h > >>> +++ b/include/linux/btf.h > >>> @@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo > >>> *btf_type_var_secinfo( > >>> const struct btf_type *btf_type_by_id(const struct btf *btf, u32 > >>> type_id); > >>> const char *btf_name_by_offset(const struct btf *btf, u32 offset); > >>> struct btf *btf_parse_vmlinux(void); > >>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES > >>> +struct btf *bpf_get_btf_module(const char *name); > >>> +#else > >>> +static inline struct btf *bpf_get_btf_module(const char *name) > >>> +{ > >>> + return ERR_PTR(-ENOTSUPP); > >>> +} > >>> +#endif > >>> struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog); > >>> #else > >>> static inline const struct btf_type *btf_type_by_id(const struct btf > >>> *btf, > >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > >>> index 162999b..26978be 100644 > >>> --- a/include/uapi/linux/bpf.h > >>> +++ b/include/uapi/linux/bpf.h > >>> @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { > >>> * the pointer data is carried out to avoid kernel crashes > >>> during > >>> * operation. Smaller types can use string space on the > >>> stack; > >>> * larger programs can use map data to store the string > >>> - * representation. > >>> + * representation. Module-specific data structures can be > >>> + * displayed if the module name is supplied. > >>> * > >>> * The string can be subsequently shared with userspace via > >>> * bpf_perf_event_output() or ring buffer interfaces. > >>> @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { > >>> * potentially to specify additional details about the BTF pointer > >>> * (rather than its mode of display) - is included for future use. > >>> * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. > >>> + * A module name can be specified for module-specific data. > >>> */ > >>> struct btf_ptr { > >>> void *ptr; > >>> __u32 type_id; > >>> __u32 flags; /* BTF ptr flags; unused at present. */ > >>> + const char *module; /* optional module name. */ > >> > >> I think module name is a wrong API here, similarly how type name was > >> wrong API for specifying the type (and thus we use type_id here). > >> Using the module's BTF ID seems like a more suitable interface. That's > >> what I'm going to use for all kinds of existing BPF APIs that expect > >> BTF type to attach BPF programs. > >> > >> Right now, we use only type_id and implicitly know that it's in > >> vmlinux BTF. With module BTFs, we now need a pair of BTF object ID + > >> BTF type ID to uniquely identify the type. vmlinux BTF now can be > >> specified in two different ways: either leaving BTF object ID as zero > >> (for simplicity and backwards compatibility) or specifying it's actual > >> BTF obj ID (which pretty much always should be 1, btw). This feels > >> like a natural extension, WDYT? > >> > >> And similar to type_id, no one should expect users to specify these > >> IDs by hand, Clang built-in and libbpf should work together to figure > >> this out for the kernel to use. > >> > >> BTW, with module names there is an extra problem for end users. Some > >> types could be either built-in or built as a module (e.g., XFS data > >> structures). Why would we require BPF users to care which is the case > >> on any given host? > > > > +1. > > As much as possible libbpf should try to hide the difference between > > type in a module vs type in the vmlinux, since that difference most of the > > time is irrelevant from bpf prog pov. > All sounds good to me - I've split out the libbpf fix and put together an updated patchset for the helpers/test which converts the currently unused __u32 "flags" field in struct btf_ptr to an "obj_id" field. If obj_id is > 1 it is presumed to be a module ID. I'd suggest we could move ahead with those changes, using the more clunky methods to retrieve the module-specific BTF id, and later fix up the test to use Yonghong's __builtin_btf_type_id() modification. Does that sound reasonable? In connection to this, I wonder if libbpf could benefit from a simple helper btf__id() (similar to btf__fd()), allowing easy retrieval of the object ID associated with module BTF? I suspect we will always have cases in general-purpose tracers where we need to look up BTF ids of objects dynamically, so such a function would help in that case. > I just crafted a llvm patch where for __builtin_btf_type_id(), a 64bit value > is returned instead of a 32bit value. libbpf can use the lower > 32bit as the btf_type_id and upper 32bit as the kernel module btf id. > > https://reviews.llvm.org/D91489 > > feel free to experiment with it to see whether it helps. > > Great! I'll give it a try, thanks! Alan
On Sun, Nov 15, 2020 at 2:53 AM Alan Maguire <alan.maguire@oracle.com> wrote: > > On Sat, 14 Nov 2020, Yonghong Song wrote: > > > > > > > On 11/14/20 8:04 AM, Alexei Starovoitov wrote: > > > On Fri, Nov 13, 2020 at 10:59 PM Andrii Nakryiko > > > <andrii.nakryiko@gmail.com> wrote: > > >> > > >> On Fri, Nov 13, 2020 at 10:11 AM Alan Maguire <alan.maguire@oracle.com> > > >> wrote: > > >>> > > >>> bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *" > > >>> argument that specifies type information about the type to > > >>> be displayed. Augment this information to include a module > > >>> name, allowing such display to support module types. > > >>> > > >>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com> > > >>> --- > > >>> include/linux/btf.h | 8 ++++++++ > > >>> include/uapi/linux/bpf.h | 5 ++++- > > >>> kernel/bpf/btf.c | 18 ++++++++++++++++++ > > >>> kernel/trace/bpf_trace.c | 42 > > >>> ++++++++++++++++++++++++++++++++---------- > > >>> tools/include/uapi/linux/bpf.h | 5 ++++- > > >>> 5 files changed, 66 insertions(+), 12 deletions(-) > > >>> > > >>> diff --git a/include/linux/btf.h b/include/linux/btf.h > > >>> index 2bf6418..d55ca00 100644 > > >>> --- a/include/linux/btf.h > > >>> +++ b/include/linux/btf.h > > >>> @@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo > > >>> *btf_type_var_secinfo( > > >>> const struct btf_type *btf_type_by_id(const struct btf *btf, u32 > > >>> type_id); > > >>> const char *btf_name_by_offset(const struct btf *btf, u32 offset); > > >>> struct btf *btf_parse_vmlinux(void); > > >>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES > > >>> +struct btf *bpf_get_btf_module(const char *name); > > >>> +#else > > >>> +static inline struct btf *bpf_get_btf_module(const char *name) > > >>> +{ > > >>> + return ERR_PTR(-ENOTSUPP); > > >>> +} > > >>> +#endif > > >>> struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog); > > >>> #else > > >>> static inline const struct btf_type *btf_type_by_id(const struct btf > > >>> *btf, > > >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > >>> index 162999b..26978be 100644 > > >>> --- a/include/uapi/linux/bpf.h > > >>> +++ b/include/uapi/linux/bpf.h > > >>> @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { > > >>> * the pointer data is carried out to avoid kernel crashes > > >>> during > > >>> * operation. Smaller types can use string space on the > > >>> stack; > > >>> * larger programs can use map data to store the string > > >>> - * representation. > > >>> + * representation. Module-specific data structures can be > > >>> + * displayed if the module name is supplied. > > >>> * > > >>> * The string can be subsequently shared with userspace via > > >>> * bpf_perf_event_output() or ring buffer interfaces. > > >>> @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { > > >>> * potentially to specify additional details about the BTF pointer > > >>> * (rather than its mode of display) - is included for future use. > > >>> * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. > > >>> + * A module name can be specified for module-specific data. > > >>> */ > > >>> struct btf_ptr { > > >>> void *ptr; > > >>> __u32 type_id; > > >>> __u32 flags; /* BTF ptr flags; unused at present. */ > > >>> + const char *module; /* optional module name. */ > > >> > > >> I think module name is a wrong API here, similarly how type name was > > >> wrong API for specifying the type (and thus we use type_id here). > > >> Using the module's BTF ID seems like a more suitable interface. That's > > >> what I'm going to use for all kinds of existing BPF APIs that expect > > >> BTF type to attach BPF programs. > > >> > > >> Right now, we use only type_id and implicitly know that it's in > > >> vmlinux BTF. With module BTFs, we now need a pair of BTF object ID + > > >> BTF type ID to uniquely identify the type. vmlinux BTF now can be > > >> specified in two different ways: either leaving BTF object ID as zero > > >> (for simplicity and backwards compatibility) or specifying it's actual > > >> BTF obj ID (which pretty much always should be 1, btw). This feels > > >> like a natural extension, WDYT? > > >> > > >> And similar to type_id, no one should expect users to specify these > > >> IDs by hand, Clang built-in and libbpf should work together to figure > > >> this out for the kernel to use. > > >> > > >> BTW, with module names there is an extra problem for end users. Some > > >> types could be either built-in or built as a module (e.g., XFS data > > >> structures). Why would we require BPF users to care which is the case > > >> on any given host? > > > > > > +1. > > > As much as possible libbpf should try to hide the difference between > > > type in a module vs type in the vmlinux, since that difference most of the > > > time is irrelevant from bpf prog pov. > > > > All sounds good to me - I've split out the libbpf fix and yeah, thanks, I've applied yesterday. > put together an updated patchset for the helpers/test which > converts the currently unused __u32 "flags" field in > struct btf_ptr to an "obj_id" field. If obj_id is > 1 it I haven't seen your updated patches (you haven't sent them yet?). You shouldn't assume obj_id == 1 means vmlinux, though. struct btf in kernel would have kernel_btf == true and its name should be "vmlinux" for vmlinux BTF, otherwise kernel_btf == true means module BTF. We can add separate bool just to distinguish vmlinux vs module BTF, if it makes life easier, I think. > is presumed to be a module ID. I'd suggest we could move > ahead with those changes, using the more clunky methods > to retrieve the module-specific BTF id, and later fix up > the test to use Yonghong's __builtin_btf_type_id() > modification. Does that sound reasonable? Yonghong already updated Clang. Corresponding libbpf changes are very minimal, feel free to add them as well. If not, I'm going to do it this week anyways. Is there any hurry to land this before the proper module BTF lands in libbpf, though? > > In connection to this, I wonder if libbpf could > benefit from a simple helper btf__id() (similar > to btf__fd()), allowing easy retrieval of the > object ID associated with module BTF? I suspect > we will always have cases in general-purpose > tracers where we need to look up BTF ids of > objects dynamically, so such a function would > help in that case. We can add that as a convenience wrapper on top of bpf_obj_get_info_by_fd() and cache the result internally, yes. > > > I just crafted a llvm patch where for __builtin_btf_type_id(), a 64bit value > > is returned instead of a 32bit value. libbpf can use the lower > > 32bit as the btf_type_id and upper 32bit as the kernel module btf id. > > > > https://reviews.llvm.org/D91489 > > > > feel free to experiment with it to see whether it helps. > > > > > > Great! I'll give it a try, thanks! > > Alan
diff --git a/include/linux/btf.h b/include/linux/btf.h index 2bf6418..d55ca00 100644 --- a/include/linux/btf.h +++ b/include/linux/btf.h @@ -209,6 +209,14 @@ static inline const struct btf_var_secinfo *btf_type_var_secinfo( const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id); const char *btf_name_by_offset(const struct btf *btf, u32 offset); struct btf *btf_parse_vmlinux(void); +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES +struct btf *bpf_get_btf_module(const char *name); +#else +static inline struct btf *bpf_get_btf_module(const char *name) +{ + return ERR_PTR(-ENOTSUPP); +} +#endif struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog); #else static inline const struct btf_type *btf_type_by_id(const struct btf *btf, diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 162999b..26978be 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { * the pointer data is carried out to avoid kernel crashes during * operation. Smaller types can use string space on the stack; * larger programs can use map data to store the string - * representation. + * representation. Module-specific data structures can be + * displayed if the module name is supplied. * * The string can be subsequently shared with userspace via * bpf_perf_event_output() or ring buffer interfaces. @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { * potentially to specify additional details about the BTF pointer * (rather than its mode of display) - is included for future use. * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. + * A module name can be specified for module-specific data. */ struct btf_ptr { void *ptr; __u32 type_id; __u32 flags; /* BTF ptr flags; unused at present. */ + const char *module; /* optional module name. */ }; /* diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 6b2d508..3ddd1fd 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5738,6 +5738,24 @@ struct btf_module { static LIST_HEAD(btf_modules); static DEFINE_MUTEX(btf_module_mutex); +struct btf *bpf_get_btf_module(const char *name) +{ + struct btf *btf = ERR_PTR(-ENOENT); + struct btf_module *btf_mod, *tmp; + + mutex_lock(&btf_module_mutex); + list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) { + if (!btf_mod->btf || strcmp(name, btf_mod->btf->name) != 0) + continue; + + refcount_inc(&btf_mod->btf->refcnt); + btf = btf_mod->btf; + break; + } + mutex_unlock(&btf_module_mutex); + return btf; +} + static ssize_t btf_module_read(struct file *file, struct kobject *kobj, struct bin_attribute *bin_attr, diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index cfce60a..a4d5a26 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -73,8 +73,7 @@ static struct bpf_raw_event_map *bpf_get_raw_tracepoint_module(const char *name) u64 bpf_get_stack(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5); static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size, - u64 flags, const struct btf **btf, - s32 *btf_id); + u64 flags, struct btf **btf, s32 *btf_id); /** * trace_call_bpf - invoke BPF program @@ -784,7 +783,7 @@ struct bpf_seq_printf_buf { BPF_CALL_4(bpf_seq_printf_btf, struct seq_file *, m, struct btf_ptr *, ptr, u32, btf_ptr_size, u64, flags) { - const struct btf *btf; + struct btf *btf; s32 btf_id; int ret; @@ -792,7 +791,11 @@ struct bpf_seq_printf_buf { if (ret) return ret; - return btf_type_seq_show_flags(btf, btf_id, ptr->ptr, m, flags); + ret = btf_type_seq_show_flags(btf, btf_id, ptr->ptr, m, flags); + if (btf_ptr_size == sizeof(struct btf_ptr) && ptr->module) + btf_put(btf); + + return ret; } static const struct bpf_func_proto bpf_seq_printf_btf_proto = { @@ -1199,18 +1202,33 @@ static bool bpf_d_path_allowed(const struct bpf_prog *prog) BTF_F_PTR_RAW | BTF_F_ZERO) static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size, - u64 flags, const struct btf **btf, + u64 flags, struct btf **btf, s32 *btf_id) { + char modname[MODULE_NAME_LEN]; const struct btf_type *t; + int ret; if (unlikely(flags & ~(BTF_F_ALL))) return -EINVAL; - if (btf_ptr_size != sizeof(struct btf_ptr)) + /* For backwards compatibility, ensure that we support BPF + * programs compiled with older "struct btf_ptr" definitions + * that lacked the "module" field. + */ + if (btf_ptr_size != sizeof(struct btf_ptr) && + btf_ptr_size != sizeof(struct btf_ptr) - sizeof(char *)) return -EINVAL; - *btf = bpf_get_btf_vmlinux(); + if (btf_ptr_size == sizeof(struct btf_ptr) && ptr->module) { + ret = copy_from_kernel_nofault(modname, ptr->module, + sizeof(modname)); + if (ret) + return ret; + + *btf = bpf_get_btf_module(modname); + } else + *btf = bpf_get_btf_vmlinux(); if (IS_ERR_OR_NULL(*btf)) return PTR_ERR(*btf); @@ -1231,7 +1249,7 @@ static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size, BPF_CALL_5(bpf_snprintf_btf, char *, str, u32, str_size, struct btf_ptr *, ptr, u32, btf_ptr_size, u64, flags) { - const struct btf *btf; + struct btf *btf; s32 btf_id; int ret; @@ -1239,8 +1257,12 @@ static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size, if (ret) return ret; - return btf_type_snprintf_show(btf, btf_id, ptr->ptr, str, str_size, - flags); + ret = btf_type_snprintf_show(btf, btf_id, ptr->ptr, str, str_size, + flags); + if (btf_ptr_size == sizeof(struct btf_ptr) && ptr->module) + btf_put(btf); + + return ret; } const struct bpf_func_proto bpf_snprintf_btf_proto = { diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 162999b..26978be 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -3636,7 +3636,8 @@ struct bpf_stack_build_id { * the pointer data is carried out to avoid kernel crashes during * operation. Smaller types can use string space on the stack; * larger programs can use map data to store the string - * representation. + * representation. Module-specific data structures can be + * displayed if the module name is supplied. * * The string can be subsequently shared with userspace via * bpf_perf_event_output() or ring buffer interfaces. @@ -5076,11 +5077,13 @@ struct bpf_sk_lookup { * potentially to specify additional details about the BTF pointer * (rather than its mode of display) - is included for future use. * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately. + * A module name can be specified for module-specific data. */ struct btf_ptr { void *ptr; __u32 type_id; __u32 flags; /* BTF ptr flags; unused at present. */ + const char *module; /* optional module name. */ }; /*
bpf_snprintf_btf and bpf_seq_printf_btf use a "struct btf_ptr *" argument that specifies type information about the type to be displayed. Augment this information to include a module name, allowing such display to support module types. Signed-off-by: Alan Maguire <alan.maguire@oracle.com> --- include/linux/btf.h | 8 ++++++++ include/uapi/linux/bpf.h | 5 ++++- kernel/bpf/btf.c | 18 ++++++++++++++++++ kernel/trace/bpf_trace.c | 42 ++++++++++++++++++++++++++++++++---------- tools/include/uapi/linux/bpf.h | 5 ++++- 5 files changed, 66 insertions(+), 12 deletions(-)