On Wed, 2023-12-20 at 11:20 -0800, Alexei Starovoitov wrote: > On Wed, Dec 20, 2023 at 5:34 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote: > > This RFC does not handle type pt_regs used for kprobes/ > > This type is defined in architecture specific headers like > > arch/x86/include/asm/ptrace.h and is hidden behind typedef > > bpf_user_pt_regs_t in include/uapi/asm-generic/bpf_perf_event.h. > > There are two ways to handle struct pt_regs: > > 1. Modify all architecture specific ptrace.h files to use __bpf_ctx; > > 2. Add annotated forward declaration for pt_regs in > > include/uapi/asm-generic/bpf_perf_event.h, e.g. as follows: > > > > #if __has_attribute(preserve_static_offset) && defined(__bpf__) > > #define __bpf_ctx __attribute__((preserve_static_offset)) > > #else > > #define __bpf_ctx > > #endif > > > > struct __bpf_ctx pt_regs; > > > > #undef __bpf_ctx > > > > #include <linux/ptrace.h> > > > > /* Export kernel pt_regs structure */ > > typedef struct pt_regs bpf_user_pt_regs_t; > > > > Unfortunately, it might be the case that option (2) is not sufficient, > > as at-least BPF selftests access pt_regs either via vmlinux.h or by > > directly including ptrace.h. > > > > If option (1) is to be implemented, it feels unreasonable to continue > > copying definition of __bpf_ctx macro from file to file. > > Given absence of common uapi exported headers between bpf.h and > > bpf_perf_event.h/ptrace.h, it looks like a new uapi header would have > > to be added, e.g. include/uapi/bpf_compiler.h. > > For the moment this header would contain only the definition for > > __bpf_ctx, and would be included in bpf.h, nf_bpf_link.h and > > architecture specific ptrace.h. > > > > Please advise. > > I'm afraid option 1 is a non starter. bpf quirks cannot impose > such heavy tax on the kernel. > > Option 2 is equally hacky. > > I think we should do what v2 did and hard code pt_regs in bpftool. I agree on (1). As for (2), I use the same hack in current patch for bpftool to avoid hacking main logic of BPF dump, it works and is allowed by C language standard (albeit in vague terms, but example is present). Unfortunately (2) does not propagate to vmlinux.h. Quentin, Alan, what do you think about hard-coding only pt_regs?
