On 11/10/21 8:40 AM, Alexei Starovoitov wrote:
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?
Yes, you try clang -> vmlinux dwarf part of step 4 with
the following kernel hack:
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 05ceb2e92b0e..30e199c30a53 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -32,7 +32,7 @@ static inline void __chk_io_ptr(const volatile void
__iomem *ptr) { }
# ifdef STRUCTLEAK_PLUGIN
# define __user __attribute__((user))
# else
-# define __user
+# define __user __attribute__((btf_type_tag("user")))
# endif
# define __iomem
# define __percpu
[yhs@devbig309.ftw3 ~/work/bpf-next]
