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Date: Mon, 26 Apr 2021 20:28:37 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...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 Mon, Apr 26, 2021 at 03:35:16PM -0700, Andrii Nakryiko wrote:
> 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$s.map_fd, 0);\n",
> > + ident, bpf_map_mmap_sz(map));
>
> use codegen()?
why?
codegen() would add extra early \n for no good reason.
> > + }
> > + codegen("\
> > + \n\
> > + return 0; \n\
> > + } \n\
> > + \n\
> > + static inline struct %1$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
I think it reads fine as-is, but, sure, I can add {}
> > + 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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