On Mon, Feb 7, 2022 at 9:16 PM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
>
> Andrii says: "... with CO-RE and vmlinux.h it would be more reliable
> and straightforward to just stick to kernel-internal struct pt_regs
> everywhere ...".
>
> Actually, if vmlinux.h is available, then it's ok to do so for both
> CO-RE and non-CO-RE cases, since the beginning of struct pt_regs must
> match (struct) user_pt_regs, which must never change.
>
> Implement this by not defining __PT_REGS_CAST if the user included
> vmlinux.h.
>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
If we are using CO-RE we don't have to assume vmlinux.h, we can define
our own definition of pt_regs with custom "flavor":
struct pt_regs___s390x {
long gprs[10];
long orig_gpr2; /* whatever the right types and names, but order
doesn't matter */
} __attribute__((preserve_access_index));
And then use `struct pt_regs__s390x` for s390x macros. That way we
don't assume any specific included header, we have minimal definition
we need (and it can be different for each architecture. It's still
CO-RE, still relocatable, and we don't need all these ugly #if
defined() checks.
> tools/lib/bpf/bpf_tracing.h | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
> index 7a015ee8fb11..07e291d77e83 100644
> --- a/tools/lib/bpf/bpf_tracing.h
> +++ b/tools/lib/bpf/bpf_tracing.h
> @@ -118,8 +118,11 @@
>
> #define __BPF_ARCH_HAS_SYSCALL_WRAPPER
>
> +#if !defined(__KERNEL__) && !defined(__VMLINUX_H__)
> /* s390 provides user_pt_regs instead of struct pt_regs to userspace */
> #define __PT_REGS_CAST(x) ((const user_pt_regs *)(x))
> +#endif
> +
> #define __PT_PARM1_REG gprs[2]
> #define __PT_PARM2_REG gprs[3]
> #define __PT_PARM3_REG gprs[4]
> @@ -148,8 +151,11 @@
>
> #define __BPF_ARCH_HAS_SYSCALL_WRAPPER
>
> +#if !defined(__KERNEL__) && !defined(__VMLINUX_H__)
> /* arm64 provides struct user_pt_regs instead of struct pt_regs to userspace */
> #define __PT_REGS_CAST(x) ((const struct user_pt_regs *)(x))
> +#endif
> +
> #define __PT_PARM1_REG regs[0]
> #define __PT_PARM2_REG regs[1]
> #define __PT_PARM3_REG regs[2]
> @@ -207,7 +213,10 @@
>
> #elif defined(bpf_target_riscv)
>
> +#if !defined(__KERNEL__) && !defined(__VMLINUX_H__)
> #define __PT_REGS_CAST(x) ((const struct user_regs_struct *)(x))
> +#endif
> +
> #define __PT_PARM1_REG a0
> #define __PT_PARM2_REG a1
> #define __PT_PARM3_REG a2
> --
> 2.34.1
>
