When generating a skeleton which has an mmaped map field, bpftool's
output is missing the map structure. This causes a compile break when
the generated skeleton is compiled as the field belongs to the internal
struct maps, not directly to the obj.
Signed-off-by: Michael Mullin <[email protected]>
---
tools/bpf/bpftool/gen.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index f158dc1c2149..b49293795ba0 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
i, bpf_map__name(map), i, ident);
/* memory-mapped internal maps */
if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) {
- printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
+ printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n",
i, ident);
}
i++;
--
2.36.1
On Mon, May 23, 2022 at 1:26 PM Michael Mullin <[email protected]> wrote:
>
> When generating a skeleton which has an mmaped map field, bpftool's
> output is missing the map structure. This causes a compile break when
> the generated skeleton is compiled as the field belongs to the internal
> struct maps, not directly to the obj.
>
> Signed-off-by: Michael Mullin <[email protected]>
> ---
> tools/bpf/bpftool/gen.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index f158dc1c2149..b49293795ba0 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
> i, bpf_map__name(map), i, ident);
> /* memory-mapped internal maps */
> if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) {
> - printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
> + printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n",
That's not right. maps.my_map is struct bpf_map *, but mmaped is
supposed to be a blob of memory that is memory-mapped into map.
Can you elaborate on how you trigger that compilation error with a
small example?
> i, ident);
> }
> i++;
> --
> 2.36.1
>
On Mon, May 23, 2022 at 03:02:31PM -0700, Andrii Nakryiko wrote:
> On Mon, May 23, 2022 at 1:26 PM Michael Mullin <[email protected]> wrote:
> >
> > When generating a skeleton which has an mmaped map field, bpftool's
> > output is missing the map structure. This causes a compile break when
> > the generated skeleton is compiled as the field belongs to the internal
> > struct maps, not directly to the obj.
> >
> > Signed-off-by: Michael Mullin <[email protected]>
> > ---
> > tools/bpf/bpftool/gen.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> > index f158dc1c2149..b49293795ba0 100644
> > --- a/tools/bpf/bpftool/gen.c
> > +++ b/tools/bpf/bpftool/gen.c
> > @@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
> > i, bpf_map__name(map), i, ident);
> > /* memory-mapped internal maps */
> > if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) {
> > - printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
> > + printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n",
>
> That's not right. maps.my_map is struct bpf_map *, but mmaped is
> supposed to be a blob of memory that is memory-mapped into map.
>
> Can you elaborate on how you trigger that compilation error with a
> small example?
I have an a very small example on github. I have added some sed fixes to
my Makefile make my sample program compile.
https://github.com/masmullin2000/libbpf-sample/tree/main/c/simple
https://github.com/masmullin2000/libbpf-sample/tree/02c7f945bf9027daedec04f485a320ba2df28204/c/simple
contains broken code.
I apologize if this is an incorrect way to share external code. I
haven't found the proper way to share example code from
kernelnewbies.org
>
> > i, ident);
> > }
> > i++;
> > --
> > 2.36.1
> >
On Mon, May 23, 2022 at 03:38:03PM -0700, Andrii Nakryiko wrote:
> On Mon, May 23, 2022 at 3:19 PM Michael Mullin <[email protected]> wrote:
> >
> > On Mon, May 23, 2022 at 03:02:31PM -0700, Andrii Nakryiko wrote:
> > > On Mon, May 23, 2022 at 1:26 PM Michael Mullin <[email protected]> wrote:
> > > >
> > > > When generating a skeleton which has an mmaped map field, bpftool's
> > > > output is missing the map structure. This causes a compile break when
> > > > the generated skeleton is compiled as the field belongs to the internal
> > > > struct maps, not directly to the obj.
> > > >
> > > > Signed-off-by: Michael Mullin <[email protected]>
> > > > ---
> > > > tools/bpf/bpftool/gen.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> > > > index f158dc1c2149..b49293795ba0 100644
> > > > --- a/tools/bpf/bpftool/gen.c
> > > > +++ b/tools/bpf/bpftool/gen.c
> > > > @@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
> > > > i, bpf_map__name(map), i, ident);
> > > > /* memory-mapped internal maps */
> > > > if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) {
> > > > - printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
> > > > + printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n",
> > >
> > > That's not right. maps.my_map is struct bpf_map *, but mmaped is
> > > supposed to be a blob of memory that is memory-mapped into map.
> > >
> > > Can you elaborate on how you trigger that compilation error with a
> > > small example?
> >
> > I have an a very small example on github. I have added some sed fixes to
> > my Makefile make my sample program compile.
> > https://github.com/masmullin2000/libbpf-sample/tree/main/c/simple
> >
> > https://github.com/masmullin2000/libbpf-sample/tree/02c7f945bf9027daedec04f485a320ba2df28204/c/simple
> > contains broken code.
>
> You are missing -g when calling clang to generate debug info (DWARF
> and subsequently BTF). When BPF object file doesn't have BTF, we don't
> generate those bss/data/rodata/etc sections of the skeleton. You
> should be good just by adding -g.
>
Thank you. By using -g, I am also unable to trigger the segfault
I was trying to fix with the patch
https://lore.kernel.org/bpf/20220523194917.igkgorco42537arb@jup/T/#u
I am not sure if there would be other ways to trigger the segfault.
> >
> > I apologize if this is an incorrect way to share external code. I
> > haven't found the proper way to share example code from
> > kernelnewbies.org
> >
> > >
> > > > i, ident);
> > > > }
> > > > i++;
> > > > --
> > > > 2.36.1
> > > >
On Mon, May 23, 2022 at 3:19 PM Michael Mullin <[email protected]> wrote:
>
> On Mon, May 23, 2022 at 03:02:31PM -0700, Andrii Nakryiko wrote:
> > On Mon, May 23, 2022 at 1:26 PM Michael Mullin <[email protected]> wrote:
> > >
> > > When generating a skeleton which has an mmaped map field, bpftool's
> > > output is missing the map structure. This causes a compile break when
> > > the generated skeleton is compiled as the field belongs to the internal
> > > struct maps, not directly to the obj.
> > >
> > > Signed-off-by: Michael Mullin <[email protected]>
> > > ---
> > > tools/bpf/bpftool/gen.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> > > index f158dc1c2149..b49293795ba0 100644
> > > --- a/tools/bpf/bpftool/gen.c
> > > +++ b/tools/bpf/bpftool/gen.c
> > > @@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
> > > i, bpf_map__name(map), i, ident);
> > > /* memory-mapped internal maps */
> > > if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) {
> > > - printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
> > > + printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n",
> >
> > That's not right. maps.my_map is struct bpf_map *, but mmaped is
> > supposed to be a blob of memory that is memory-mapped into map.
> >
> > Can you elaborate on how you trigger that compilation error with a
> > small example?
>
> I have an a very small example on github. I have added some sed fixes to
> my Makefile make my sample program compile.
> https://github.com/masmullin2000/libbpf-sample/tree/main/c/simple
>
> https://github.com/masmullin2000/libbpf-sample/tree/02c7f945bf9027daedec04f485a320ba2df28204/c/simple
> contains broken code.
You are missing -g when calling clang to generate debug info (DWARF
and subsequently BTF). When BPF object file doesn't have BTF, we don't
generate those bss/data/rodata/etc sections of the skeleton. You
should be good just by adding -g.
>
> I apologize if this is an incorrect way to share external code. I
> haven't found the proper way to share example code from
> kernelnewbies.org
>
> >
> > > i, ident);
> > > }
> > > i++;
> > > --
> > > 2.36.1
> > >