Re: [PATCH v2 bpf-next 15/16] bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

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@gmail.com> wrote:
> >
> > From: Alexei Starovoitov <ast@kernel.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@kernel.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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