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Commit 1f2ed153 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Arnaldo Carvalho de Melo
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perf probe: Fix to get correct modname from elf header 



Since 'perf probe' supports cross-arch probes, it is possible to analyze
different arch kernel image which has different bits-per-long.

In that case, it fails to get the module name because it uses the
MOD_NAME_OFFSET macro based on the host machine bits-per-long, instead
of the target arch bits-per-long.

This fixes above issue by changing modname-offset based on the target
archs bit width. This is ok because linux kernel uses LP64 model on
64bit arch.

E.g. without this (on x86_64, and target module is arm32):

  $ perf probe -m build-arm/fs/configfs/configfs.ko -D configfs_lookup
  p:probe/configfs_lookup :configfs_lookup+0
                          ^-Here is an empty module name.

With this fix, you can see correct module name:

  $ perf probe -m build-arm/fs/configfs/configfs.ko -D configfs_lookup
  p:probe/configfs_lookup configfs:configfs_lookup+0

Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/148337043836.6752.383495516397005695.stgit@devbox


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent b6f4c667

tools/perf/util/probe-event.c

+16 −16
Original line number Diff line number Diff line
@@ -267,21 +267,6 @@ static bool kprobe_warn_out_range(const char *symbol, unsigned long address) 
	return true;

}



/*

 * NOTE:

 * '.gnu.linkonce.this_module' section of kernel module elf directly

 * maps to 'struct module' from linux/module.h. This section contains

 * actual module name which will be used by kernel after loading it.

 * But, we cannot use 'struct module' here since linux/module.h is not

 * exposed to user-space. Offset of 'name' has remained same from long

 * time, so hardcoding it here.

 */

#ifdef __LP64__

#define MOD_NAME_OFFSET 24

#else

#define MOD_NAME_OFFSET 12

#endif



/*

 * @module can be module name of module file path. In case of path,

 * inspect elf and find out what is actual module name.
@@ -296,6 +281,7 @@ static char *find_module_name(const char *module) 
	Elf_Data *data;

	Elf_Scn *sec;

	char *mod_name = NULL;

	int name_offset;



	fd = open(module, O_RDONLY);

	if (fd < 0)
@@ -317,7 +303,21 @@ static char *find_module_name(const char *module) 
	if (!data || !data->d_buf)

		goto ret_err;



	mod_name = strdup((char *)data->d_buf + MOD_NAME_OFFSET);

	/*

	 * NOTE:

	 * '.gnu.linkonce.this_module' section of kernel module elf directly

	 * maps to 'struct module' from linux/module.h. This section contains

	 * actual module name which will be used by kernel after loading it.

	 * But, we cannot use 'struct module' here since linux/module.h is not

	 * exposed to user-space. Offset of 'name' has remained same from long

	 * time, so hardcoding it here.

	 */

	if (ehdr.e_ident[EI_CLASS] == ELFCLASS32)

		name_offset = 12;

	else	/* expect ELFCLASS64 by default */

		name_offset = 24;



	mod_name = strdup((char *)data->d_buf + name_offset);



ret_err:

	elf_end(elf);