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Message-ID: <CAEf4BzbY2qM7OfmjfJVO1LhSYyk-NTCEo=UykH+XxKcKcPuC7w@mail.gmail.com>
Date: Mon, 26 Apr 2021 15:35:16 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 15/16] bpftool: Use syscall/loader program in
"prog load" and "gen skeleton" command.
On Thu, Apr 22, 2021 at 5:27 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> From: Alexei Starovoitov <ast@...nel.org>
>
> Add -L flag to bpftool to use libbpf gen_trace facility and syscall/loader program
> for skeleton generation and program loading.
>
> "bpftool gen skeleton -L" command will generate a "light skeleton" or "loader skeleton"
> that is similar to existing skeleton, but has one major difference:
> $ bpftool gen skeleton lsm.o > lsm.skel.h
> $ bpftool gen skeleton -L lsm.o > lsm.lskel.h
> $ diff lsm.skel.h lsm.lskel.h
> @@ -5,34 +4,34 @@
> #define __LSM_SKEL_H__
>
> #include <stdlib.h>
> -#include <bpf/libbpf.h>
> +#include <bpf/bpf.h>
>
> The light skeleton does not use majority of libbpf infrastructure.
> It doesn't need libelf. It doesn't parse .o file.
> It only needs few sys_bpf wrappers. All of them are in bpf/bpf.h file.
> In future libbpf/bpf.c can be inlined into bpf.h, so not even libbpf.a would be
> needed to work with light skeleton.
>
> "bpftool prog load -L file.o" command is introduced for debugging of syscall/loader
> program generation. Just like the same command without -L it will try to load
> the programs from file.o into the kernel. It won't even try to pin them.
>
> "bpftool prog load -L -d file.o" command will provide additional debug messages
> on how syscall/loader program was generated.
> Also the execution of syscall/loader program will use bpf_trace_printk() for
> each step of loading BTF, creating maps, and loading programs.
> The user can do "cat /.../trace_pipe" for further debug.
>
> An example of fexit_sleep.lskel.h generated from progs/fexit_sleep.c:
> struct fexit_sleep {
> struct bpf_loader_ctx ctx;
> struct {
> struct bpf_map_desc bss;
> } maps;
> struct {
> struct bpf_prog_desc nanosleep_fentry;
> struct bpf_prog_desc nanosleep_fexit;
> } progs;
> struct {
> int nanosleep_fentry_fd;
> int nanosleep_fexit_fd;
> } links;
> struct fexit_sleep__bss {
> int pid;
> int fentry_cnt;
> int fexit_cnt;
> } *bss;
> };
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
> tools/bpf/bpftool/Makefile | 2 +-
> tools/bpf/bpftool/gen.c | 313 +++++++++++++++++++++++++++---
> tools/bpf/bpftool/main.c | 7 +-
> tools/bpf/bpftool/main.h | 1 +
> tools/bpf/bpftool/prog.c | 80 ++++++++
> tools/bpf/bpftool/xlated_dumper.c | 3 +
> 6 files changed, 382 insertions(+), 24 deletions(-)
>
[...]
> @@ -268,6 +269,254 @@ static void codegen(const char *template, ...)
> free(s);
> }
>
> +static void print_hex(const char *obj_data, int file_sz)
> +{
> + int i, len;
> +
> + /* embed contents of BPF object file */
nit: this comment should have stayed at the original place
> + for (i = 0, len = 0; i < file_sz; i++) {
> + int w = obj_data[i] ? 4 : 2;
> +
[...]
> + bpf_object__for_each_map(map, obj) {
> + const char * ident;
> +
> + ident = get_map_ident(map);
> + if (!ident)
> + continue;
> +
> + if (!bpf_map__is_internal(map) ||
> + !(bpf_map__def(map)->map_flags & BPF_F_MMAPABLE))
> + continue;
> +
> + printf("\tskel->%1$s =\n"
> + "\t\tmmap(NULL, %2$zd, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED,\n"
> + "\t\t\tskel->maps.%1$s.map_fd, 0);\n",
> + ident, bpf_map_mmap_sz(map));
use codegen()?
> + }
> + codegen("\
> + \n\
> + return 0; \n\
> + } \n\
> + \n\
> + static inline struct %1$s * \n\
[...]
> static int do_skeleton(int argc, char **argv)
> {
> char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
> @@ -277,7 +526,7 @@ static int do_skeleton(int argc, char **argv)
> struct bpf_object *obj = NULL;
> const char *file, *ident;
> struct bpf_program *prog;
> - int fd, len, err = -1;
> + int fd, err = -1;
> struct bpf_map *map;
> struct btf *btf;
> struct stat st;
> @@ -359,7 +608,25 @@ static int do_skeleton(int argc, char **argv)
> }
>
> get_header_guard(header_guard, obj_name);
> - codegen("\
> + if (use_loader)
please use {} for such a long if/else, even if it's, technically, a
single-statement if
> + codegen("\
> + \n\
> + /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */ \n\
> + /* THIS FILE IS AUTOGENERATED! */ \n\
> + #ifndef %2$s \n\
> + #define %2$s \n\
> + \n\
> + #include <stdlib.h> \n\
> + #include <bpf/bpf.h> \n\
> + #include <bpf/skel_internal.h> \n\
> + \n\
> + struct %1$s { \n\
> + struct bpf_loader_ctx ctx; \n\
> + ",
> + obj_name, header_guard
> + );
> + else
> + codegen("\
> \n\
> /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */ \n\
> \n\
[...]
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