Subject: Re: [PATCH v8 bpf-next 08/13] bpf: Add BTF_SET_START/END macros

From: Jiri Olsa <[email-masked]>
Date: Wed, 29 Jul 2020 13:54:29 +0200

On Tue, Jul 28, 2020 at 12:39:06PM -0700, Andrii Nakryiko wrote:

SNIP

> 
> [...]
> 
> > +#define BTF_SET_START(name)                            \
> > +__BTF_ID_LIST(name, local)                             \
> > +asm(                                                   \
> > +".pushsection " BTF_IDS_SECTION ",\"a\";       \n"     \
> > +".local __BTF_ID__set__" #name ";              \n"     \
> > +"__BTF_ID__set__" #name ":;                    \n"     \
> > +".zero 4                                       \n"     \
> > +".popsection;                                  \n");
> > +
> > +#define BTF_SET_END(name)                              \
> > +asm(                                                   \
> > +".pushsection " BTF_IDS_SECTION ",\"a\";      \n"      \
> > +".size __BTF_ID__set__" #name ", .-" #name "  \n"      \
> > +".popsection;                                 \n");    \
> > +extern struct btf_id_set name;
> > +
> >  #else
> 
> This local symbol assumption will probably at some point bite us.
> Yonghong already did global vs static variants for BTF ID list, we'll
> end up doing something like that for sets of BTF IDs as well. Let's do
> this similarly from the get go.

sure, will add that

> 
> >
> >  #define BTF_ID_LIST(name) static u32 name[5];
> >  #define BTF_ID(prefix, name)
> >  #define BTF_ID_UNUSED
> >  #define BTF_ID_LIST_GLOBAL(name) u32 name[1];
> > +#define BTF_SET_START(name) static struct btf_id_set name = { 0 };
> 
> nit: this zero is unnecessary and misleading (it's initialized for
> only the first member of a struct). Just {} is enough.

ok

> 
> > +#define BTF_SET_END(name)
> >
> >  #endif /* CONFIG_DEBUG_INFO_BTF */
> >
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 562d4453fad3..06714cdda0a9 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -21,6 +21,8 @@
> >  #include <linux/btf_ids.h>
> >  #include <linux/skmsg.h>
> >  #include <linux/perf_event.h>
> > +#include <linux/bsearch.h>
> > +#include <linux/btf_ids.h>
> >  #include <net/sock.h>
> >
> >  /* BTF (BPF Type Format) is the meta data format which describes
> > @@ -4740,3 +4742,15 @@ u32 btf_id(const struct btf *btf)
> >  {
> >         return btf->id;
> >  }
> > +
> > +static int btf_id_cmp_func(const void *a, const void *b)
> > +{
> > +       const int *pa = a, *pb = b;
> > +
> > +       return *pa - *pb;
> > +}
> > +
> > +bool btf_id_set_contains(struct btf_id_set *set, u32 id)
> > +{
> > +       return bsearch(&id, set->ids, set->cnt, sizeof(int), btf_id_cmp_func) != NULL;
> 
> very nit ;) sizeof(__u32)

sure ;-)

thanks,
jirka