netdev - Re: [PATCHv2 bpf-next] selftests/bpf: Fix test_attach

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Date:   Sat, 6 Mar 2021 19:13:17 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Yauheni Kaliuta <ykaliuta@...hat.com>
Subject: Re: [PATCHv2 bpf-next] selftests/bpf: Fix test_attach_probe for
 powerpc uprobes

On Fri, Mar 5, 2021 at 5:42 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> When testing uprobes we the test gets GEP (Global Entry Point)
> address from kallsyms, but then the function is called locally
> so the uprobe is not triggered.
>
> Fixing this by adjusting the address to LEP (Local Entry Point)
> for powerpc arch plus instruction check stolen from ppc_function_entry
> function pointed out and explained by Michael and Naveen.
>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  .../selftests/bpf/prog_tests/attach_probe.c   | 40 ++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
> index a0ee87c8e1ea..9dc4e3dfbcf3 100644
> --- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
> +++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
> @@ -2,6 +2,44 @@
>  #include <test_progs.h>
>  #include "test_attach_probe.skel.h"
>
> +#if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
> +
> +#define OP_RT_RA_MASK   0xffff0000UL
> +#define LIS_R2          0x3c400000UL
> +#define ADDIS_R2_R12    0x3c4c0000UL
> +#define ADDI_R2_R2      0x38420000UL
> +
> +static ssize_t get_offset(ssize_t addr, ssize_t base)
> +{
> +       u32 *insn = (u32 *) addr;
> +
> +       /*
> +        * A PPC64 ABIv2 function may have a local and a global entry
> +        * point. We need to use the local entry point when patching
> +        * functions, so identify and step over the global entry point
> +        * sequence.
> +        *
> +        * The global entry point sequence is always of the form:
> +        *
> +        * addis r2,r12,XXXX
> +        * addi  r2,r2,XXXX
> +        *
> +        * A linker optimisation may convert the addis to lis:
> +        *
> +        * lis   r2,XXXX
> +        * addi  r2,r2,XXXX
> +        */
> +       if ((((*insn & OP_RT_RA_MASK) == ADDIS_R2_R12) ||
> +            ((*insn & OP_RT_RA_MASK) == LIS_R2)) &&
> +           ((*(insn + 1) & OP_RT_RA_MASK) == ADDI_R2_R2))
> +               return (ssize_t)(insn + 2) - base;
> +       else
> +               return addr - base;
> +}
> +#else
> +#define get_offset(addr, base) (addr - base)

I turned this into a static function, not sure why you preferred
#define here. Applied to bpf-next.

> +#endif
> +
>  ssize_t get_base_addr() {
>         size_t start, offset;
>         char buf[256];
> @@ -36,7 +74,7 @@ void test_attach_probe(void)
>         if (CHECK(base_addr < 0, "get_base_addr",
>                   "failed to find base addr: %zd", base_addr))
>                 return;
> -       uprobe_offset = (size_t)&get_base_addr - base_addr;
> +       uprobe_offset = get_offset((size_t)&get_base_addr, base_addr);
>
>         skel = test_attach_probe__open_and_load();
>         if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
> --
> 2.27.0
>