[RFC PATCH 6/8] perf tools powerpc: Fix PPC64 ELF ABIv2 symbol decoding

From: Naveen N. Rao
Date: Tue Dec 09 2014 - 12:35:55 EST


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.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
tools/perf/arch/powerpc/Makefile | 1 +
tools/perf/arch/powerpc/util/elf-sym-decode.c | 27 +++++++++++++++++++++++++++
tools/perf/config/Makefile | 1 +
tools/perf/util/elf_sym.h | 13 +++++++++++++
tools/perf/util/symbol-elf.c | 8 ++++++++
5 files changed, 50 insertions(+)
create mode 100644 tools/perf/arch/powerpc/util/elf-sym-decode.c
create mode 100644 tools/perf/util/elf_sym.h

diff --git a/tools/perf/arch/powerpc/Makefile b/tools/perf/arch/powerpc/Makefile
index 6f7782b..8621439 100644
--- a/tools/perf/arch/powerpc/Makefile
+++ b/tools/perf/arch/powerpc/Makefile
@@ -3,4 +3,5 @@ PERF_HAVE_DWARF_REGS := 1
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/dwarf-regs.o
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/skip-callchain-idx.o
endif
+LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/elf-sym-decode.o
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/header.o
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)
+
+unsigned int arch_elf_sym_decode_offset(GElf_Sym *sym)
+{
+ return PPC64_LOCAL_ENTRY_OFFSET(sym->st_other);
+}
diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
index 58f6091..8f64557 100644
--- a/tools/perf/config/Makefile
+++ b/tools/perf/config/Makefile
@@ -378,6 +378,7 @@ ifeq ($(ARCH),powerpc)
ifndef NO_DWARF
CFLAGS += -DHAVE_SKIP_CALLCHAIN_IDX
endif
+ CFLAGS += -DHAVE_ELF_SYM_DECODE
endif

ifndef NO_LIBUNWIND
diff --git a/tools/perf/util/elf_sym.h b/tools/perf/util/elf_sym.h
new file mode 100644
index 0000000..0176f21
--- /dev/null
+++ b/tools/perf/util/elf_sym.h
@@ -0,0 +1,13 @@
+#ifndef __PERF_ELF_SYM_H
+#define __PERF_ELF_SYM_H
+
+#ifdef HAVE_ELF_SYM_DECODE
+extern unsigned int arch_elf_sym_decode_offset(GElf_Sym *sym);
+#else
+static inline unsigned int arch_elf_sym_decode_offset(GElf_Sym *sym __maybe_unused)
+{
+ return 0;
+}
+#endif
+
+#endif /* __PERF_ELF_SYM_H */
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);
+
if (dso->kernel || kmodule) {
char dso_name[PATH_MAX];

--
2.1.3

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