perf probe: Fix to get correct modname from elf header (1f2ed153) · Commits · 戴 / test

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:

Masami 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:

Arnaldo Carvalho de Melo <acme@redhat.com>

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);

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