perf probe: Find given address from offline dwarf

Find the given address from offline dwarfs instead of online kernel
dwarfs.

On the KASLR enabled kernel, the kernel text section is loaded with
random offset, and the debuginfo__new_online_kernel can't handle it. So
let's move to the offline dwarf loader instead of using the online dwarf
loader.

As a result, since we don't need debuginfo__new_online_kernel any more,
this also removes the functions related to that.

Without this change;

  # ./perf probe -l
    probe:t_show         (on _stext+901288 with m v)
    probe:t_show_1       (on _stext+939624 with m v t)
    probe:t_show_2       (on _stext+980296 with m v fmt)
    probe:t_show_3       (on _stext+1014392 with m v file)

With this change;

  # ./perf probe -l
    probe:t_show         (on t_show@linux-3/kernel/trace/ftrace.c with m v)
    probe:t_show_1       (on t_show@linux-3/kernel/trace/trace.c with m v t)
    probe:t_show_2       (on t_show@kernel/trace/trace_printk.c with m v fmt)
    probe:t_show_3       (on t_show@kernel/trace/trace_events.c with m v file)

Changes from v2:
 - Instead of retrying, directly opens offline dwarf.
 - Remove debuginfo__new_online_kernel and related functions.
 - Refer map->reloc to get the correct address of a symbol.
 - Add a special case for handling ref_reloc_sym based address.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: "David A. Long" <dave.long@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20140206053218.29635.74821.stgit@kbuild-fedora.yrl.intra.hitachi.co.jpSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -248,6 +248,18 @@ static struct debuginfo *open_debuginfo(const char *module)
 	return debuginfo__new(path);
 }
 
+static struct ref_reloc_sym *__kernel_get_ref_reloc_sym(void)
+{
+	/* kmap->ref_reloc_sym should be set if host_machine is initialized */
+	struct kmap *kmap;
+
+	if (map__load(host_machine->vmlinux_maps[MAP__FUNCTION], NULL) < 0)
+		return NULL;
+
+	kmap = map__kmap(host_machine->vmlinux_maps[MAP__FUNCTION]);
+	return kmap->ref_reloc_sym;
+}
+
 /*
  * Convert trace point to probe point with debuginfo
  * Currently only handles kprobes.
@@ -256,18 +268,27 @@ static int kprobe_convert_to_perf_probe(struct probe_trace_point *tp,
 					struct perf_probe_point *pp)
 {
 	struct symbol *sym;
+	struct ref_reloc_sym *reloc_sym;
 	struct map *map;
-	u64 addr;
+	u64 addr = 0;
 	int ret = -ENOENT;
 	struct debuginfo *dinfo;
 
-	sym = __find_kernel_function_by_name(tp->symbol, &map);
-	if (sym) {
-		addr = map->unmap_ip(map, sym->start + tp->offset);
+	/* ref_reloc_sym is just a label. Need a special fix*/
+	reloc_sym = __kernel_get_ref_reloc_sym();
+	if (reloc_sym && strcmp(tp->symbol, reloc_sym->name) == 0)
+		addr = reloc_sym->unrelocated_addr + tp->offset;
+	else {
+		sym = __find_kernel_function_by_name(tp->symbol, &map);
+		if (sym)
+			addr = map->unmap_ip(map, sym->start + tp->offset) -
+				map->reloc;
+	}
+	if (addr) {
 		pr_debug("try to find %s+%ld@%" PRIx64 "\n", tp->symbol,
 			 tp->offset, addr);
 
-		dinfo = debuginfo__new_online_kernel(addr);
+		dinfo = open_debuginfo(tp->module);
 		if (dinfo) {
 			ret = debuginfo__find_probe_point(dinfo,
 						 (unsigned long)addr, pp);
@@ -383,15 +404,6 @@ static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
 	return ret;
 }
 
-static struct ref_reloc_sym *__kernel_get_ref_reloc_sym(void)
-{
-	/* kmap->ref_reloc_sym should be set if host_machine is initialized */
-	struct kmap *kmap;
-
-	kmap = map__kmap(host_machine->vmlinux_maps[MAP__FUNCTION]);
-	return kmap->ref_reloc_sym;
-}
-
 /* Post processing the probe events */
 static int post_process_probe_trace_events(struct probe_trace_event *tevs,
 					   int ntevs, const char *module,

tools/perf/util/probe-finder.c

@@ -89,79 +89,6 @@ static int debuginfo__init_offline_dwarf(struct debuginfo *dbg,
 	return -ENOENT;
 }
 
-#if _ELFUTILS_PREREQ(0, 148)
-/* This method is buggy if elfutils is older than 0.148 */
-static int __linux_kernel_find_elf(Dwfl_Module *mod,
-				   void **userdata,
-				   const char *module_name,
-				   Dwarf_Addr base,
-				   char **file_name, Elf **elfp)
-{
-	int fd;
-	const char *path = kernel_get_module_path(module_name);
-
-	pr_debug2("Use file %s for %s\n", path, module_name);
-	if (path) {
-		fd = open(path, O_RDONLY);
-		if (fd >= 0) {
-			*file_name = strdup(path);
-			return fd;
-		}
-	}
-	/* If failed, try to call standard method */
-	return dwfl_linux_kernel_find_elf(mod, userdata, module_name, base,
-					  file_name, elfp);
-}
-
-static const Dwfl_Callbacks kernel_callbacks = {
-	.find_debuginfo = dwfl_standard_find_debuginfo,
-	.debuginfo_path = &debuginfo_path,
-
-	.find_elf = __linux_kernel_find_elf,
-	.section_address = dwfl_linux_kernel_module_section_address,
-};
-
-/* Get a Dwarf from live kernel image */
-static int debuginfo__init_online_kernel_dwarf(struct debuginfo *dbg,
-					       Dwarf_Addr addr)
-{
-	dbg->dwfl = dwfl_begin(&kernel_callbacks);
-	if (!dbg->dwfl)
-		return -EINVAL;
-
-	/* Load the kernel dwarves: Don't care the result here */
-	dwfl_linux_kernel_report_kernel(dbg->dwfl);
-	dwfl_linux_kernel_report_modules(dbg->dwfl);
-
-	dbg->dbg = dwfl_addrdwarf(dbg->dwfl, addr, &dbg->bias);
-	/* Here, check whether we could get a real dwarf */
-	if (!dbg->dbg) {
-		pr_debug("Failed to find kernel dwarf at %lx\n",
-			 (unsigned long)addr);
-		dwfl_end(dbg->dwfl);
-		memset(dbg, 0, sizeof(*dbg));
-		return -ENOENT;
-	}
-
-	return 0;
-}
-#else
-/* With older elfutils, this just support kernel module... */
-static int debuginfo__init_online_kernel_dwarf(struct debuginfo *dbg,
-					       Dwarf_Addr addr __maybe_unused)
-{
-	const char *path = kernel_get_module_path("kernel");
-
-	if (!path) {
-		pr_err("Failed to find vmlinux path\n");
-		return -ENOENT;
-	}
-
-	pr_debug2("Use file %s for debuginfo\n", path);
-	return debuginfo__init_offline_dwarf(dbg, path);
-}
-#endif
-
 struct debuginfo *debuginfo__new(const char *path)
 {
 	struct debuginfo *dbg = zalloc(sizeof(*dbg));
@@ -174,19 +101,6 @@ struct debuginfo *debuginfo__new(const char *path)
 	return dbg;
 }
 
-struct debuginfo *debuginfo__new_online_kernel(unsigned long addr)
-{
-	struct debuginfo *dbg = zalloc(sizeof(*dbg));
-
-	if (!dbg)
-		return NULL;
-
-	if (debuginfo__init_online_kernel_dwarf(dbg, (Dwarf_Addr)addr) < 0)
-		zfree(&dbg);
-
-	return dbg;
-}
-
 void debuginfo__delete(struct debuginfo *dbg)
 {
 	if (dbg) {

tools/perf/util/probe-finder.h

@@ -31,7 +31,6 @@ struct debuginfo {
 };
 
 extern struct debuginfo *debuginfo__new(const char *path);
-extern struct debuginfo *debuginfo__new_online_kernel(unsigned long addr);
 extern void debuginfo__delete(struct debuginfo *dbg);
 
 /* Find probe_trace_events specified by perf_probe_event from debuginfo */