netdev - Re: [PATCH v3 bpf-next 3/4] selftests/bpf: make PT_REGS

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Date:   Tue, 9 Jul 2019 10:48:52 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Stanislav Fomichev <sdf@...ichev.me>,
        Y Song <ys114321@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH v3 bpf-next 3/4] selftests/bpf: make PT_REGS_* work in userspace

On Tue, Jul 9, 2019 at 8:19 AM Ilya Leoshkevich <iii@...ux.ibm.com> wrote:
>
> Right now, on certain architectures, these macros are usable only with
> kernel headers. This patch makes it possible to use them with userspace
> headers and, as a consequence, not only in BPF samples, but also in BPF
> selftests.
>
> On s390, provide the forward declaration of struct pt_regs and cast it
> to user_pt_regs in PT_REGS_* macros. This is necessary, because instead
> of the full struct pt_regs, s390 exposes only its first member
> user_pt_regs to userspace, and bpf_helpers.h is used with both userspace
> (in selftests) and kernel (in samples) headers. It was added in commit
> 466698e654e8 ("s390/bpf: correct broken uapi for
> BPF_PROG_TYPE_PERF_EVENT program type").
>
> Ditto on arm64.
>
> On x86, provide userspace versions of PT_REGS_* macros. Unlike s390 and
> arm64, x86 provides struct pt_regs to both userspace and kernel, however,
> with different member names.
>
> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
> ---

Just curious, what did you use as a reference for which register
corresponds to which PARM, RET, etc for different archs? I've tried to
look it up the other day, and it wasn't as straightforward to find as
I hoped for, so maybe I'm missing something obvious.


>  tools/testing/selftests/bpf/bpf_helpers.h | 61 +++++++++++++++--------
>  1 file changed, 41 insertions(+), 20 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
> index 73071a94769a..212ec564e5c3 100644
> --- a/tools/testing/selftests/bpf/bpf_helpers.h
> +++ b/tools/testing/selftests/bpf/bpf_helpers.h
> @@ -358,6 +358,7 @@ static int (*bpf_skb_adjust_room)(void *ctx, __s32 len_diff, __u32 mode,
>
>  #if defined(bpf_target_x86)
>
> +#ifdef __KERNEL__
>  #define PT_REGS_PARM1(x) ((x)->di)
>  #define PT_REGS_PARM2(x) ((x)->si)
>  #define PT_REGS_PARM3(x) ((x)->dx)
> @@ -368,19 +369,35 @@ static int (*bpf_skb_adjust_room)(void *ctx, __s32 len_diff, __u32 mode,
>  #define PT_REGS_RC(x) ((x)->ax)
>  #define PT_REGS_SP(x) ((x)->sp)
>  #define PT_REGS_IP(x) ((x)->ip)
> +#else
> +#define PT_REGS_PARM1(x) ((x)->rdi)
> +#define PT_REGS_PARM2(x) ((x)->rsi)
> +#define PT_REGS_PARM3(x) ((x)->rdx)
> +#define PT_REGS_PARM4(x) ((x)->rcx)
> +#define PT_REGS_PARM5(x) ((x)->r8)
> +#define PT_REGS_RET(x) ((x)->rsp)
> +#define PT_REGS_FP(x) ((x)->rbp)
> +#define PT_REGS_RC(x) ((x)->rax)
> +#define PT_REGS_SP(x) ((x)->rsp)
> +#define PT_REGS_IP(x) ((x)->rip)

Will this also work for 32-bit x86?

> +#endif

<snip>