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.
