On 2014/12/10 09:13PM, Michael Ellerman wrote:
> On Tue, 2014-12-09 at 23:04 +0530, Naveen N. Rao wrote:
> > PPC64 ELF ABIv2 has a Global Entry Point (GEP) and a Local Entry Point
> > (LEP). For purposes of probing, we need the LEP. Offset to the LEP is
> > encoded in st_other.
> >
> > diff --git a/tools/perf/arch/powerpc/util/elf-sym-decode.c
> > b/tools/perf/arch/powerpc/util/elf-sym-decode.c
> > new file mode 100644
> > index 0000000..7434656
> > --- /dev/null
> > +++ b/tools/perf/arch/powerpc/util/elf-sym-decode.c
> > @@ -0,0 +1,27 @@
> > +/*
> > + * Decode offset from Global Entry Point to Local Entry Point on PPC64
> > + * ELF ABIv2.
> > + *
> > + * Derived from definitions in arch/powerpc/kernel/module_64.c
> > + *
> > + * Copyright (C) 2014 Ananth N Mavinakayanahalli, IBM Corporation.
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; either version
> > + * 2 of the License, or (at your option) any later version.
> > + */
> > +
> > +#include <gelf.h>
> > +#include "elf_sym.h"
> > +
> > +/* PowerPC64 ABIv2 specific values for the ELF64_Sym st_other field. */
> > +#define STO_PPC64_LOCAL_BIT 5
> > +#define STO_PPC64_LOCAL_MASK (7 << STO_PPC64_LOCAL_BIT)
> > +#define PPC64_LOCAL_ENTRY_OFFSET(other)
> > \
> > + (((1 << (((other) & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT)) >> 2)
> > << 2)
>
> You're in userspace, you should be able to get these from elf.h
Ah, ok.
>
> > +unsigned int arch_elf_sym_decode_offset(GElf_Sym *sym)
> > +{
> > + return PPC64_LOCAL_ENTRY_OFFSET(sym->st_other);
>
> What happens on ABIv1 ? We hope st_other is zero?
Yes, st_other is zero in ABIv1.
>
> > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> > index 67e4392..92a424e 100644
> > --- a/tools/perf/util/symbol-elf.c
> > +++ b/tools/perf/util/symbol-elf.c
> > @@ -10,6 +10,7 @@
> > #include "vdso.h"
> > #include <symbol/kallsyms.h>
> > #include "debug.h"
> > +#include "elf_sym.h"
> >
> > #ifndef HAVE_ELF_GETPHDRNUM_SUPPORT
> > static int elf_getphdrnum(Elf *elf, size_t *dst)
> > @@ -848,6 +849,13 @@ int dso__load_sym(struct dso *dso, struct map *map,
> > (sym.st_value & 1))
> > --sym.st_value;
> >
> > + /*
> > + * PPC64 ELF ABIv2 encodes Local Entry Point offset in
> > + * the st_other field
> > + */
> > + if ((map->type == MAP__FUNCTION) && sym.st_other)
> > + sym.st_value += arch_elf_sym_decode_offset(&sym);
>
> I guess no other arch has needed to do anything like this.
>
> But if they did it's unlikely they'll want to do the exact same logic, ie.
> check st_other and add some value to st_value. To make it more generically
> useful you could just make it:
>
> > + if (map->type == MAP__FUNCTION)
> > + arch_elf_sym_decode(&sym);
>
> And do any other checks in the arch routine.
Sure. Makes sense.
- Naveen
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