perf events: Fix mmap offset determination

Fix buggy-looking code which unnecessarily adjusts the file offset
fields read from /proc/*/maps.

This may have gone unnoticed since the offset is usually 0 (and the
logic in util/symbol.c may work incorrectly for other offset values).

Commiter note:

This fixes a bug introduced in 4af8b35d, there is no need to shift pgoff
twice, the show_map_vma routine in fs/proc/task_mmu.c already converts
it from the number of pages to the size in bytes, and that is what
appears in /proc/PID/map.

Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Will Deacon <Will.Deacon@arm.com>
LKML-Reference: <1280836116-6654-2-git-send-email-dave.martin@linaro.org>
Signed-off-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/event.c

@@ -151,7 +151,6 @@ static int event__synthesize_mmap_events(pid_t pid, pid_t tgid,
 			continue;
 		pbf += n + 3;
 		if (*pbf == 'x') { /* vm_exec */
-			u64 vm_pgoff;
 			char *execname = strchr(bf, '/');
 
 			/* Catch VDSO */
@@ -162,12 +161,7 @@ static int event__synthesize_mmap_events(pid_t pid, pid_t tgid,
 				continue;
 
 			pbf += 3;
-			n = hex2u64(pbf, &vm_pgoff);
-			/* pgoff is in bytes, not pages */
-			if (n >= 0)
-				ev.mmap.pgoff = vm_pgoff << getpagesize();
-			else
-				ev.mmap.pgoff = 0;
+			n = hex2u64(pbf, &ev.mmap.pgoff);
 
 			size = strlen(execname);
 			execname[size - 1] = '\0'; /* Remove \n */