perf_counter tools: Adjust only prelinked symbol's addresses

I.e. we can't handle these two kinds of files in the same way:

1) prelinked system library:

[acme@doppio pahole]$ readelf -s /usr/lib64/libdw-0.141.so | egrep 'FUNC.+GLOBAL.+dwfl_report_elf'
   278: 00000030450105a0   261 FUNC    GLOBAL DEFAULT   12 dwfl_report_elf@@ELFUTILS_0.122

2) not prelinked library with debug information from a -debuginfo package:

[acme@doppio pahole]$ readelf -s /usr/lib/debug/usr/lib64/libdw-0.141.so.debug | egrep 'FUNC.+GLOBAL.+dwfl_report_elf'
   629: 00000000000105a0   261 FUNC    GLOBAL DEFAULT   12 dwfl_report_elf
[acme@doppio pahole]$

Now the numbers I got for a pahole perf run are in line with
the numbers I get from oprofile.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20090630144317.GB12663@ghostprotocols.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/util/symbol.c

@@ -520,7 +520,9 @@ static int dso__load_sym(struct dso *self, int fd, const char *name,
 	nr_syms = shdr.sh_size / shdr.sh_entsize;
 
 	memset(&sym, 0, sizeof(sym));
-
+	self->prelinked = elf_section_by_name(elf, &ehdr, &shdr,
+					      ".gnu.prelink_undo",
+					      NULL) != NULL;
 	elf_symtab__for_each_symbol(syms, nr_syms, index, sym) {
 		struct symbol *f;
 		u64 obj_start;
@@ -535,11 +537,13 @@ static int dso__load_sym(struct dso *self, int fd, const char *name,
 		gelf_getshdr(sec, &shdr);
 		obj_start = sym.st_value;
 
+		if (self->prelinked) {
 			if (verbose >= 2)
 				printf("adjusting symbol: st_value: %Lx sh_addr: %Lx sh_offset: %Lx\n",
 					(u64)sym.st_value, (u64)shdr.sh_addr, (u64)shdr.sh_offset);
 
 			sym.st_value -= shdr.sh_addr - shdr.sh_offset;
+		}
 
 		f = symbol__new(sym.st_value, sym.st_size,
 				elf_sym__name(&sym, symstrs),
@@ -573,6 +577,8 @@ int dso__load(struct dso *self, symbol_filter_t filter, int verbose)
 	if (!name)
 		return -1;
 
+	self->prelinked = 0;
+
 	if (strncmp(self->name, "/tmp/perf-", 10) == 0)
 		return dso__load_perf_map(self, filter, verbose);
 

tools/perf/util/symbol.h

@@ -20,8 +20,9 @@ struct symbol {
 struct dso {
 	struct list_head node;
 	struct rb_root	 syms;
-	unsigned int	 sym_priv_size;
 	struct symbol    *(*find_symbol)(struct dso *, u64 ip);
+	unsigned int	 sym_priv_size;
+	unsigned char	 prelinked;
 	char		 name[0];
 };