Re: [PATCH] perf tools: add compatibility with libelf 0.8 and autodetect

[Marti Raudsepp]

On Sat, Oct 24, 2009 at 12:52 AM, Ingo Molnar <mingo@xxxxxxx> wrote:
> Mind adding a comment as well to document the version dependency?

Sure

> Also, there's a few probably unintended whitespaces

Fixed

--
perf tools: add compatibility with libelf 0.8 and autodetect

The Makefile now automatically defines LIBELF_NO_MMAP when libelf 0.8 is
detected. libelf 0.8 is still maintained and some distributions such as
Arch Linux use it instead of elfutils.

Signed-off-by: Marti Raudsepp <marti@xxxxxxxxx>
---
 tools/perf/Makefile      |    6 +++++-
 tools/perf/util/symbol.c |    9 +++++----
 tools/perf/util/symbol.h |   16 ++++++++++++++++
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/tools/perf/Makefile b/tools/perf/Makefile
index 742a32e..46e877b 100644
--- a/tools/perf/Makefile
+++ b/tools/perf/Makefile
@@ -422,7 +422,11 @@ ifeq ($(uname_S),Darwin)
 	PTHREAD_LIBS =
 endif
 
-ifneq ($(shell sh -c "(echo '\#include <libelf.h>'; echo 'int main(void) { Elf * elf = elf_begin(0, ELF_C_READ_MMAP, 0); return (long)elf; }') | $(CC) -x c - $(ALL_CFLAGS) -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -o /dev/null $(ALL_LDFLAGS) > /dev/null 2>&1 && echo y"), y)
+ifeq ($(shell sh -c "(echo '\#include <libelf.h>'; echo 'int main(void) { Elf * elf = elf_begin(0, ELF_C_READ, 0); return (long)elf; }') | $(CC) -x c - $(ALL_CFLAGS) -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -o /dev/null $(ALL_LDFLAGS) > /dev/null 2>&1 && echo y"), y)
+	ifneq ($(shell sh -c "(echo '\#include <libelf.h>'; echo 'int main(void) { Elf * elf = elf_begin(0, ELF_C_READ_MMAP, 0); return (long)elf; }') | $(CC) -x c - $(ALL_CFLAGS) -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -o /dev/null $(ALL_LDFLAGS) > /dev/null 2>&1 && echo y"), y)
+		BASIC_CFLAGS += -DLIBELF_NO_MMAP
+	endif
+else
 	msg := $(error No libelf.h/libelf found, please install libelf-dev/elfutils-libelf-devel and glibc-dev[el]);
 endif
 
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 47ea060..ec69c42 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -5,7 +5,6 @@
 
 #include "debug.h"
 
-#include <libelf.h>
 #include <gelf.h>
 #include <elf.h>
 
@@ -413,7 +412,8 @@ static int dso__synthesize_plt_symbols(struct  dso *self, int v)
 	if (fd < 0)
 		goto out;
 
-	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+	elf = perf_elf_begin(fd, ELF_C_READ, NULL);
+
 	if (elf == NULL)
 		goto out_close;
 
@@ -533,7 +533,8 @@ static int dso__load_sym(struct dso *self, int fd, const char *name,
 	Elf *elf;
 	int nr = 0, kernel = !strcmp("[kernel]", self->name);
 
-	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+	elf = perf_elf_begin(fd, ELF_C_READ, NULL);
+
 	if (elf == NULL) {
 		if (v)
 			fprintf(stderr, "%s: cannot read %s ELF file.\n",
@@ -675,7 +676,7 @@ static char *dso__read_build_id(struct dso *self, int v)
 	if (fd < 0)
 		goto out;
 
-	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+	elf = perf_elf_begin(fd, ELF_C_READ, NULL);
 	if (elf == NULL) {
 		if (v)
 			fprintf(stderr, "%s: cannot read %s ELF file.\n",
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 6e84907..38bc832 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -8,6 +8,8 @@
 #include "module.h"
 #include "event.h"
 
+#include <libelf.h>
+
 #ifdef HAVE_CPLUS_DEMANGLE
 extern char *cplus_demangle(const char *, int);
 
@@ -27,6 +29,20 @@ static inline char *bfd_demangle(void __used *v, const char __used *c,
 #endif
 #endif
 
+static inline Elf *perf_elf_begin(int fd, Elf_Cmd cmd, Elf *ref)
+{
+#ifndef LIBELF_NO_MMAP
+	/*
+	 * libelf 0.8 and earlier do not support ELF_C_READ_MMAP; for newer
+	 * versions we can use mmap to reduce memory usage
+	 */
+
+	if (cmd == ELF_C_READ)
+		cmd = ELF_C_READ_MMAP;
+#endif
+	return elf_begin(fd, cmd, ref);
+}
+
 #ifndef DMGL_PARAMS
 #define DMGL_PARAMS      (1 << 0)       /* Include function args */
 #define DMGL_ANSI        (1 << 1)       /* Include const, volatile, etc */
-- 
1.6.5.1

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