| Message ID | 20201104215923.4000229-2-jolsa@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | pahole/kernel: Workaround dwarf bug for function encoding | expand |
On Wed, Nov 4, 2020 at 2:02 PM Jiri Olsa <jolsa@kernel.org> wrote: > > With upcoming changes to pahole, that change the way how and > which kernel functions are stored in BTF data, we need a way > to recognize iterator functions. > > Iterator functions need to be in BTF data, but have no real > body and are currently placed in .init.text section, so they > are freed after kernel init and are filtered out of BTF data > because of that. > > The solution is to place these functions under new section: > .init.bpf.preserve_type > > And add 2 new symbols to mark that area: > __init_bpf_preserve_type_begin > __init_bpf_preserve_type_end > > The code in pahole responsible for picking up the functions will > be able to recognize functions from this section and add them to > the BTF data and filter out all other .init.text functions. > > Suggested-by: Yonghong Song <yhs@fb.com> > Signed-off-by: Jiri Olsa <jolsa@redhat.com> Acked-by: Song Liu <songliubraving@fb.com> [...]
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index cd14444bf600..e18e1030dabf 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -685,8 +685,21 @@ .BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) { \ *(.BTF_ids) \ } + +/* + * .init.bpf.preserve_type + * + * This section store special BPF function and marks them + * with begin/end symbols pair for the sake of pahole tool. + */ +#define INIT_BPF_PRESERVE_TYPE \ + __init_bpf_preserve_type_begin = .; \ + *(.init.bpf.preserve_type) \ + __init_bpf_preserve_type_end = .; \ + MEM_DISCARD(init.bpf.preserve_type) #else #define BTF +#define INIT_BPF_PRESERVE_TYPE #endif /* @@ -740,7 +753,8 @@ #define INIT_TEXT \ *(.init.text .init.text.*) \ *(.text.startup) \ - MEM_DISCARD(init.text*) + MEM_DISCARD(init.text*) \ + INIT_BPF_PRESERVE_TYPE #define EXIT_DATA \ *(.exit.data .exit.data.*) \ diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 2fffd30e13ac..12ab39a034a3 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1276,10 +1276,16 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd); int bpf_obj_pin_user(u32 ufd, const char __user *pathname); int bpf_obj_get_user(const char __user *pathname, int flags); +#ifdef CONFIG_DEBUG_INFO_BTF +#define BPF_INIT __init_bpf_preserve_type +#else +#define BPF_INIT __init +#endif + #define BPF_ITER_FUNC_PREFIX "bpf_iter_" #define DEFINE_BPF_ITER_FUNC(target, args...) \ extern int bpf_iter_ ## target(args); \ - int __init bpf_iter_ ## target(args) { return 0; } + int BPF_INIT bpf_iter_ ## target(args) { return 0; } struct bpf_iter_aux_info { struct bpf_map *map; diff --git a/include/linux/init.h b/include/linux/init.h index 212fc9e2f691..133462863711 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -52,6 +52,7 @@ #define __initconst __section(.init.rodata) #define __exitdata __section(.exit.data) #define __exit_call __used __section(.exitcall.exit) +#define __init_bpf_preserve_type __section(.init.bpf.preserve_type) /* * modpost check for section mismatches during the kernel build.
With upcoming changes to pahole, that change the way how and which kernel functions are stored in BTF data, we need a way to recognize iterator functions. Iterator functions need to be in BTF data, but have no real body and are currently placed in .init.text section, so they are freed after kernel init and are filtered out of BTF data because of that. The solution is to place these functions under new section: .init.bpf.preserve_type And add 2 new symbols to mark that area: __init_bpf_preserve_type_begin __init_bpf_preserve_type_end The code in pahole responsible for picking up the functions will be able to recognize functions from this section and add them to the BTF data and filter out all other .init.text functions. Suggested-by: Yonghong Song <yhs@fb.com> Signed-off-by: Jiri Olsa <jolsa@redhat.com> --- include/asm-generic/vmlinux.lds.h | 16 +++++++++++++++- include/linux/bpf.h | 8 +++++++- include/linux/init.h | 1 + 3 files changed, 23 insertions(+), 2 deletions(-)