Em Fri, Nov 06, 2020 at 11:25:10PM +0100, Jiri Olsa escreveu:
> 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.
This isn't applying on torvalds/master:
[acme@five linux]$ patch -p1 < /wb/1.patch
patching file include/asm-generic/vmlinux.lds.h
Hunk #2 succeeded at 754 (offset 1 line).
patching file include/linux/bpf.h
Hunk #1 succeeded at 1276 (offset -1 lines).
patching file include/linux/init.h
Hunk #1 FAILED at 52.
1 out of 1 hunk FAILED -- saving rejects to file include/linux/init.h.rej
[acme@five linux]$
[acme@five linux]$ cat include/linux/init.h.rej
--- include/linux/init.h
+++ 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.
[acme@five linux]$
I'm fixing it up by hand to try together with pahole's patches.
- Arnaldo
> Suggested-by: Yonghong Song <yhs@xxxxxx>
> Acked-by: Song Liu <songliubraving@xxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> include/asm-generic/vmlinux.lds.h | 16 +++++++++++++++-
> include/linux/bpf.h | 8 +++++++-
> include/linux/init.h | 1 +
> 3 files changed, 23 insertions(+), 2 deletions(-)
>
> 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 73d5381a5d5c..894f66c7703e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1277,10 +1277,16 @@ 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.
> --
> 2.26.2
>
--
- Arnaldo
