[Bug runtime/17638] New: Symbol resolution broken for PPC64 ABIv2

["ananth at in dot ibm.com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17638

            Bug ID: 17638
           Summary: Symbol resolution broken for PPC64 ABIv2
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: ananth at in dot ibm.com

PPC64 ABIv2 has a facility where a function can have a Global Entry Point (GEP)
and a Local Entry Point (LEP); the LEP is at an offset from the GEP and can be
gotten to programmatically from the Elf64_Sym.st_other field. See the ABIv2
specification for more details. See arch/powerpc/kernel/module_64.c and
ppc_function_entry@arch/powerpc/include/asm/code-patching.h for more details.

Kprobes at function entry need probes installed at the LEP. The symbol table
and DWARF entry_pc/high_pc encode only the GEP instead. This needs fixing.

stap -p3 -ve 'probe kernel.function("do_fork") { printf("Hello\n"); exit() }'
... resolves do_fork as:

} stap_dwarf_probes[] = {
  { .address=(unsigned long)0x283950ULL, .module="kernel", .section="_stext",
.probe=(&stap_probes[0]), },
};

nnr:~/kprobes # grep do_fork /boot/System.map
c0000000000a6920 T do_fork

nnr:~/kprobes # stap -g -ve 'probe
kernel.statement(0xc0000000000a6928).absolute {printf("here\n") exit()}'
Pass 1: parsed user script and 102 library script(s) using
40256virt/33408res/5504shr/27072data kb, in 280usr/0sys/285real ms.
Pass 2: analyzed script: 1 probe(s), 1 function(s), 0 embed(s), 0 global(s)
using 41216virt/35584res/6656shr/28032data kb, in 10usr/0sys/8real ms.
Pass 3: translated to C into
"/tmp/stapVEC1GH/stap_9c9d5bee16716aeedfab6219de368bd7_1067_src.c" using
41216virt/36032res/7104shr/28032data kb, in 10usr/0sys/9real ms.
Pass 4: compiled C into "stap_9c9d5bee16716aeedfab6219de368bd7_1067.ko" in
2160usr/100sys/3254real ms.
Pass 5: starting run.
here
Pass 5: run completed in 50usr/90sys/28905real ms.

Now, the real question is, where should this be fixed:
Elfutils?
Dwarf encoding of entry_pc/high_pc?
Or in the end consumer tools like stap/perf?

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