Re: [PATCHv2 bpf-next] selftests/bpf: Fix test_attach_probe for powerpc uprobes

[Jiri Olsa <jolsa@redhat.com>]

On Sat, Mar 06, 2021 at 07:13:17PM -0800, Andrii Nakryiko wrote:
> On Fri, Mar 5, 2021 at 5:42 AM Jiri Olsa <jolsa@kernel.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@ellerman.id.au>
> > Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.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

seemed simple enough to be dealt with in preprocessor,
why bother compiler ;-)

> #define here. Applied to bpf-next.

thanks,
jirka