On Tue, Nov 9, 2021 at 10:26 PM Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 11/9/21 9:28 PM, Alexei Starovoitov wrote:
> > On Tue, Nov 09, 2021 at 09:19:40PM -0800, Yonghong Song wrote:
> >> LLVM patches ([1] for clang, [2] and [3] for BPF backend)
> >> added support for btf_type_tag attributes. This patch
> >> added support for the kernel.
> >>
> >> The main motivation for btf_type_tag is to bring kernel
> >> annotations __user, __rcu etc. to btf. With such information
> >> available in btf, bpf verifier can detect mis-usages
> >> and reject the program. For example, for __user tagged pointer,
> >> developers can then use proper helper like bpf_probe_read_kernel()
> >> etc. to read the data.
> >
> > +#define __tag1 __attribute__((btf_type_tag("tag1")))
> > +#define __tag2 __attribute__((btf_type_tag("tag2")))
> > +
> > +struct btf_type_tag_test {
> > + int __tag1 * __tag1 __tag2 *p;
> > +} g;
> >
> > Can we build the kernel with the latest clang and get __user in BTF ?
>
> Not yet. The following are the steps:
> 1. land this patch set in the kernel
> 2. sync to libbpf repo.
> 3. pahole sync with libbpf repo, and pahole convert btf_type_tag
> in llvm to BTF
> 4. another kernel patch to define __user as
> __attribute__((btf_type_tag("user")))
> and then we will get __user in vmlinux BTF.
Makes sense. I was wondering whether clang can handle
the whole kernel source code with
#define __user __attribute__((btf_type_tag("user")))
Steps 1,2,3 are necessary to make use of it,
but step 4 can be tried out already?
