Commit 99d00215 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Kees Cook
Browse files

objtool: Add a pass for generating __mcount_loc 

Add the --mcount option for generating __mcount_loc sections
needed for dynamic ftrace. Using this pass requires the kernel to
be compiled with -mfentry and CC_USING_NOP_MCOUNT to be defined
in Makefile.

Link: https://lore.kernel.org/lkml/20200625200235.GQ4781@hirez.programming.kicks-ass.net/


Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
[Sami: rebased, dropped config changes, fixed to actually use --mcount,
       and wrote a commit message.]
Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
parent 2b868952

tools/objtool/builtin-check.c

+2 −1
Original line number Diff line number Diff line
@@ -18,7 +18,7 @@ 
#include "builtin.h"

#include "objtool.h"



bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux;

bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux, mcount;



static const char * const check_usage[] = {

	"objtool check [<options>] file.o",
@@ -35,6 +35,7 @@ const struct option check_options[] = { 
	OPT_BOOLEAN('s', "stats", &stats, "print statistics"),

	OPT_BOOLEAN('d', "duplicate", &validate_dup, "duplicate validation for vmlinux.o"),

	OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),

	OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),

	OPT_END(),

};

tools/objtool/builtin.h

+1 −1
Original line number Diff line number Diff line
@@ -8,7 +8,7 @@ 
#include <subcmd/parse-options.h>



extern const struct option check_options[];

extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux;

extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux, mcount;



extern int cmd_check(int argc, const char **argv);

extern int cmd_orc(int argc, const char **argv);

tools/objtool/check.c

+82 −0
Original line number Diff line number Diff line
@@ -530,6 +530,65 @@ static int create_static_call_sections(struct objtool_file *file) 
	return 0;

}



static int create_mcount_loc_sections(struct objtool_file *file)

{

	struct section *sec, *reloc_sec;

	struct reloc *reloc;

	unsigned long *loc;

	struct instruction *insn;

	int idx;



	sec = find_section_by_name(file->elf, "__mcount_loc");

	if (sec) {

		INIT_LIST_HEAD(&file->mcount_loc_list);

		WARN("file already has __mcount_loc section, skipping");

		return 0;

	}



	if (list_empty(&file->mcount_loc_list))

		return 0;



	idx = 0;

	list_for_each_entry(insn, &file->mcount_loc_list, mcount_loc_node)

		idx++;



	sec = elf_create_section(file->elf, "__mcount_loc", 0, sizeof(unsigned long), idx);

	if (!sec)

		return -1;



	reloc_sec = elf_create_reloc_section(file->elf, sec, SHT_RELA);

	if (!reloc_sec)

		return -1;



	idx = 0;

	list_for_each_entry(insn, &file->mcount_loc_list, mcount_loc_node) {



		loc = (unsigned long *)sec->data->d_buf + idx;

		memset(loc, 0, sizeof(unsigned long));



		reloc = malloc(sizeof(*reloc));

		if (!reloc) {

			perror("malloc");

			return -1;

		}

		memset(reloc, 0, sizeof(*reloc));



		reloc->sym = insn->sec->sym;

		reloc->addend = insn->offset;

		reloc->type = R_X86_64_64;

		reloc->offset = idx * sizeof(unsigned long);

		reloc->sec = reloc_sec;

		elf_add_reloc(file->elf, reloc);



		idx++;

	}



	if (elf_rebuild_reloc_section(file->elf, reloc_sec))

		return -1;



	return 0;

}



/*

 * Warnings shouldn't be reported for ignored functions.

 */
@@ -956,6 +1015,22 @@ static int add_call_destinations(struct objtool_file *file) 
			insn->type = INSN_NOP;

		}



		if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {

			if (reloc) {

				reloc->type = R_NONE;

				elf_write_reloc(file->elf, reloc);

			}



			elf_write_insn(file->elf, insn->sec,

				       insn->offset, insn->len,

				       arch_nop_insn(insn->len));



			insn->type = INSN_NOP;



			list_add_tail(&insn->mcount_loc_node,

				      &file->mcount_loc_list);

		}



		/*

		 * Whatever stack impact regular CALLs have, should be undone

		 * by the RETURN of the called function.
@@ -2927,6 +3002,13 @@ int check(struct objtool_file *file) 
		goto out;

	warnings += ret;



	if (mcount) {

		ret = create_mcount_loc_sections(file);

		if (ret < 0)

			goto out;

		warnings += ret;

	}



out:

	if (ret < 0) {

		/*

tools/objtool/check.h

+1 −0
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ struct instruction { 
	struct list_head list;

	struct hlist_node hash;

	struct list_head static_call_node;

	struct list_head mcount_loc_node;

	struct section *sec;

	unsigned long offset;

	unsigned int len;

tools/objtool/objtool.c

+1 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ struct objtool_file *objtool_open_read(const char *_objname) 
	INIT_LIST_HEAD(&file.insn_list);

	hash_init(file.insn_hash);

	INIT_LIST_HEAD(&file.static_call_list);

	INIT_LIST_HEAD(&file.mcount_loc_list);

	file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");

	file.ignore_unreachables = no_unreachable;

	file.hints = false;