On 2016/03/30 10:13PM, Naveen N Rao wrote:
> While trying to address the kallsyms perf test failure on ppc64le,
> Ananth noticed that we were not necessarily probing at the expected
> address when an offset to the function was specified.
>
> So far, we used to treat probe point offsets as being offset from the
> LEP. However, userspace applications (objdump/readelf) always show
> disassembly and offsets from the function GEP. This is confusing to the
> user. Fix this by changing how we modify probe address with perf.
>
> If only the function name is provided, we assume the user needs the LEP.
> Otherwise, if an offset is specified, we assume that the user knows the
> exact address to probe based on function disassembly, and so we just
> place the probe from the GEP offset.
>
> Tested lightly. Needs more testing.
>
> Cc: Thiago Jung Bauermann <bauer...@linux.vnet.ibm.com>
> Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Reported-by: Ananth N Mavinakayanahalli <ana...@in.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> ---
> tools/perf/arch/powerpc/util/sym-handling.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/arch/powerpc/util/sym-handling.c
> b/tools/perf/arch/powerpc/util/sym-handling.c
> index 3e98a61..36f6eb0 100644
> --- a/tools/perf/arch/powerpc/util/sym-handling.c
> +++ b/tools/perf/arch/powerpc/util/sym-handling.c
> @@ -65,16 +65,23 @@ void arch__fix_tev_from_maps(struct perf_probe_event *pev,
> struct probe_trace_event *tev, struct map *map,
> struct symbol *sym)
> {
> + int lep_offset = PPC64_LOCAL_ENTRY_OFFSET(sym->elf_st_other);
> +
> /*
> * ppc64 ABIv2 local entry point is currently always 2 instructions
> - * (8 bytes) after the global entry point.
> + * (8 bytes) after the global entry point. When probing at a function
> + * entry point, we normally always want the LEP since that catches calls
> + * to the function through both the GEP and the LEP. However, if the
> user
> + * specifies an offset, we fall back to using the GEP since all
> userspace
> + * applications (objdump/readelf) show function disassembly with offsets
> + * from the GEP.
> */
> - if (!pev->uprobes && map->dso->symtab_type ==
> DSO_BINARY_TYPE__KALLSYMS) {
> - tev->point.address += PPC64LE_LEP_OFFSET;
> + if (pev->point.offset)
This needs to be:
if (pev->point.offset || pev->point.retprobe)
return;
kretprobes fails otherwise.
- Naveen
> + return;
> +
> + if (!pev->uprobes && map->dso->symtab_type == DSO_BINARY_TYPE__KALLSYMS)
> tev->point.offset += PPC64LE_LEP_OFFSET;
> - } else if (PPC64_LOCAL_ENTRY_OFFSET(sym->elf_st_other)) {
> - tev->point.address +=
> PPC64_LOCAL_ENTRY_OFFSET(sym->elf_st_other);
> - tev->point.offset +=
> PPC64_LOCAL_ENTRY_OFFSET(sym->elf_st_other);
> - }
> + else if (lep_offset)
> + tev->point.offset += lep_offset;
> }
> #endif
> --
> 2.7.4
>
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