[RFC PATCH 2/3] objtool: Enable and implement 'mcount' subcommand
From: Sathvika Vasireddy
Date: Fri Mar 18 2022 - 06:54:13 EST
This patch adds 'mcount' as a subcommand to objtool, and enables
the same for x86. objtool is built if CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
is selected. Additionally, architectures can select HAVE_NOP_MCOUNT
if they choose to nop out mcount call sites. If that config option is
selected, then --mnop is passed as an option to 'objtool mcount'
Signed-off-by: Sathvika Vasireddy <sv@xxxxxxxxxxxxx>
---
Makefile | 6 ++
arch/x86/Kconfig | 3 +-
scripts/Makefile.build | 12 +++
tools/objtool/Build | 2 +
tools/objtool/Makefile | 4 +-
tools/objtool/builtin-mcount.c | 74 +++++++++++++
tools/objtool/include/objtool/builtin.h | 4 +-
tools/objtool/include/objtool/objtool.h | 1 +
tools/objtool/mcount.c | 138 ++++++++++++++++++++++++
tools/objtool/objtool.c | 1 +
tools/objtool/weak.c | 5 +
11 files changed, 247 insertions(+), 3 deletions(-)
create mode 100644 tools/objtool/builtin-mcount.c
create mode 100644 tools/objtool/mcount.c
diff --git a/Makefile b/Makefile
index 55a30ca69350..316f7d08b30a 100644
--- a/Makefile
+++ b/Makefile
@@ -846,7 +846,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
endif
endif
ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+ ifdef CONFIG_HAVE_NOP_MCOUNT
CC_FLAGS_USING += -DCC_USING_NOP_MCOUNT
+ endif
endif
ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
ifdef CONFIG_HAVE_C_RECORDMCOUNT
@@ -1303,6 +1305,10 @@ ifdef CONFIG_STACK_VALIDATION
prepare: tools/objtool
endif
+ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+prepare: tools/objtool
+endif
+
ifdef CONFIG_BPF
ifdef CONFIG_DEBUG_INFO_BTF
prepare: tools/bpf/resolve_btfids
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9f5bd41bf660..eecfe588cd9f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -185,7 +185,8 @@ config X86
select HAVE_CONTEXT_TRACKING if X86_64
select HAVE_CONTEXT_TRACKING_OFFSTACK if HAVE_CONTEXT_TRACKING
select HAVE_C_RECORDMCOUNT
- select HAVE_OBJTOOL_MCOUNT if STACK_VALIDATION
+ select HAVE_OBJTOOL_MCOUNT
+ select HAVE_NOP_MCOUNT if HAVE_OBJTOOL_MCOUNT
select HAVE_BUILDTIME_MCOUNT_SORT
select HAVE_DEBUG_KMEMLEAK
select HAVE_DMA_CONTIGUOUS
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a4b89b757287..6a09b4ba14a1 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -242,6 +242,18 @@ cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(o
endif # CONFIG_STACK_VALIDATION
+ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+
+objtool := $(objtree)/tools/objtool/objtool
+
+objtool_args := mcount
+objtool_args += $(if $(CONFIG_HAVE_NOP_MCOUNT), --mnop)
+
+cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
+cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
+
+endif # CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+
ifdef CONFIG_LTO_CLANG
# Skip objtool for LLVM bitcode
diff --git a/tools/objtool/Build b/tools/objtool/Build
index 161fd451241a..0b9b8bd0ee92 100644
--- a/tools/objtool/Build
+++ b/tools/objtool/Build
@@ -2,12 +2,14 @@ objtool-y += arch/$(SRCARCH)/
objtool-y += weak.o
+objtool-$(SUBCMD_MCOUNT) += mcount.o
objtool-$(SUBCMD_CHECK) += check.o
objtool-$(SUBCMD_CHECK) += special.o
objtool-$(SUBCMD_ORC) += check.o
objtool-$(SUBCMD_ORC) += orc_gen.o
objtool-$(SUBCMD_ORC) += orc_dump.o
+objtool-y += builtin-mcount.o
objtool-y += builtin-check.o
objtool-y += builtin-orc.o
objtool-y += elf.o
diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 92ce4fce7bc7..8404cf696954 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -41,13 +41,15 @@ AWK = awk
SUBCMD_CHECK := n
SUBCMD_ORC := n
+SUBCMD_MCOUNT := n
ifeq ($(SRCARCH),x86)
SUBCMD_CHECK := y
SUBCMD_ORC := y
+ SUBCMD_MCOUNT := y
endif
-export SUBCMD_CHECK SUBCMD_ORC
+export SUBCMD_CHECK SUBCMD_ORC SUBCMD_MCOUNT
export srctree OUTPUT CFLAGS SRCARCH AWK
include $(srctree)/tools/build/Makefile.include
diff --git a/tools/objtool/builtin-mcount.c b/tools/objtool/builtin-mcount.c
new file mode 100644
index 000000000000..f203d118cffa
--- /dev/null
+++ b/tools/objtool/builtin-mcount.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <subcmd/parse-options.h>
+#include <string.h>
+#include <stdlib.h>
+#include <objtool/builtin.h>
+#include <objtool/objtool.h>
+
+bool mnop;
+
+static const char * const mcount_usage[] = {
+ "objtool mcount [<options>] file.o",
+ NULL,
+};
+
+static const char * const env_usage[] = {
+ "OBJTOOL_ARGS=\"<options>\"",
+ NULL,
+};
+
+const struct option mcount_options[] = {
+ OPT_BOOLEAN('N', "mnop", &mnop, "nop mcount call sites"),
+ OPT_END(),
+};
+
+int cmd_parse_options_mcount(int argc, const char **argv, const char * const usage[])
+{
+ const char *envv[16] = { };
+ char *env;
+ int envc;
+
+ env = getenv("OBJTOOL_ARGS");
+ if (env) {
+ envv[0] = "OBJTOOL_ARGS";
+ for (envc = 1; envc < ARRAY_SIZE(envv); ) {
+ envv[envc++] = env;
+ env = strchr(env, ' ');
+ if (!env)
+ break;
+ *env = '\0';
+ env++;
+ }
+
+ parse_options(envc, envv, mcount_options, env_usage, 0);
+ }
+
+ argc = parse_options(argc, argv, mcount_options, usage, 0);
+ if (argc != 1)
+ usage_with_options(usage, mcount_options);
+ return argc;
+}
+
+int cmd_mcount(int argc, const char **argv)
+{
+ const char *objname;
+ struct objtool_file *file;
+ int ret;
+
+ argc = cmd_parse_options_mcount(argc, argv, mcount_usage);
+ objname = argv[0];
+
+ file = objtool_open_read(objname);
+ if (!file)
+ return 1;
+
+ ret = objtool_mcount(file);
+ if (ret)
+ return ret;
+
+ if (file->elf->changed)
+ return elf_write(file->elf);
+
+ return 0;
+}
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 89ba869ed08f..d7ed6ff65729 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -9,11 +9,13 @@
extern const struct option check_options[];
extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
- validate_dup, vmlinux, mcount, noinstr, backup, sls;
+ validate_dup, vmlinux, mcount, noinstr, backup, sls, mnop;
extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);
+extern int cmd_parse_options_mcount(int argc, const char **argv, const char * const usage[]);
extern int cmd_check(int argc, const char **argv);
extern int cmd_orc(int argc, const char **argv);
+extern int cmd_mcount(int argc, const char **argv);
#endif /* _BUILTIN_H */
diff --git a/tools/objtool/include/objtool/objtool.h b/tools/objtool/include/objtool/objtool.h
index f99fbc6078d5..edcf28d4407c 100644
--- a/tools/objtool/include/objtool/objtool.h
+++ b/tools/objtool/include/objtool/objtool.h
@@ -41,5 +41,6 @@ void objtool_pv_add(struct objtool_file *file, int idx, struct symbol *func);
int check(struct objtool_file *file);
int orc_dump(const char *objname);
int orc_create(struct objtool_file *file);
+int objtool_mcount(struct objtool_file *file);
#endif /* _OBJTOOL_H */
diff --git a/tools/objtool/mcount.c b/tools/objtool/mcount.c
new file mode 100644
index 000000000000..fc3d215671bf
--- /dev/null
+++ b/tools/objtool/mcount.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <string.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+
+#include <arch/elf.h>
+#include <objtool/builtin.h>
+#include <objtool/cfi.h>
+#include <objtool/arch.h>
+#include <objtool/check.h>
+#include <objtool/utils.h>
+#include <objtool/special.h>
+#include <objtool/warn.h>
+
+#include <linux/objtool.h>
+#include <linux/hashtable.h>
+#include <linux/kernel.h>
+#include <linux/static_call_types.h>
+
+static int classify_symbols(struct objtool_file *file)
+{
+ struct section *sec;
+ struct symbol *func;
+
+ for_each_sec(file, sec) {
+ list_for_each_entry(func, &sec->symbol_list, list) {
+ if (func->bind != STB_GLOBAL)
+ continue;
+ if ((!strcmp(func->name, "__fentry__")) || (!strcmp(func->name, "_mcount")))
+ func->fentry = true;
+ }
+ }
+
+ return 0;
+}
+
+static void annotate_call_site(struct objtool_file *file,
+ struct instruction *insn, bool sibling)
+{
+ struct reloc *reloc = insn_reloc(file, insn);
+ struct symbol *sym = insn->call_dest;
+
+ if (!sym)
+ sym = reloc->sym;
+
+ if (sym->fentry) {
+ if (sibling)
+ WARN_FUNC("Tail call to _mcount !?!?", insn->sec, insn->offset);
+ if (mnop) {
+ 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->call_node, &file->mcount_loc_list);
+ return;
+ }
+}
+
+static void add_call_dest(struct objtool_file *file, struct instruction *insn,
+ struct symbol *dest, bool sibling)
+{
+ insn->call_dest = dest;
+ if (!dest)
+ return;
+
+ remove_insn_ops(insn);
+
+ annotate_call_site(file, insn, sibling);
+}
+static int add_call_destinations(struct objtool_file *file)
+{
+ struct instruction *insn;
+ unsigned long dest_off;
+ struct symbol *dest;
+ struct reloc *reloc;
+
+ for_each_insn(file, insn) {
+ if (insn->type != INSN_CALL)
+ continue;
+
+ reloc = insn_reloc(file, insn);
+ if (!reloc) {
+ dest_off = arch_jump_destination(insn);
+ dest = find_call_destination(insn->sec, dest_off);
+
+ add_call_dest(file, insn, dest, false);
+
+
+ } else {
+ add_call_dest(file, insn, reloc->sym, false);
+ }
+ }
+
+ return 0;
+}
+
+static int decode_sections(struct objtool_file *file)
+{
+ int ret;
+
+ ret = decode_instructions(file);
+ if (ret)
+ return ret;
+
+ ret = classify_symbols(file);
+ if (ret)
+ return ret;
+
+ ret = add_call_destinations(file);
+ if (ret)
+ return ret;
+
+ return 0;
+}
+
+
+int objtool_mcount(struct objtool_file *file)
+{
+ int ret, warnings = 0;
+
+ ret = decode_sections(file);
+ if (ret < 0)
+ return 0;
+
+ ret = create_mcount_loc_sections(file);
+ if (ret < 0)
+ return 0;
+ warnings += ret;
+ return 0;
+}
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index bdf699f6552b..e19851813d5b 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -37,6 +37,7 @@ static const char objtool_usage_string[] =
static struct cmd_struct objtool_cmds[] = {
{"check", cmd_check, "Perform stack metadata validation on an object file" },
+ {"mcount", cmd_mcount, "Generate __mcount_loc section" },
{"orc", cmd_orc, "Generate in-place ORC unwind tables for an object file" },
};
diff --git a/tools/objtool/weak.c b/tools/objtool/weak.c
index 8314e824db4a..19b2dfcacf2e 100644
--- a/tools/objtool/weak.c
+++ b/tools/objtool/weak.c
@@ -29,3 +29,8 @@ int __weak orc_create(struct objtool_file *file)
{
UNSUPPORTED("orc");
}
+
+int __weak objtool_mcount(struct objtool_file *file)
+{
+ UNSUPPORTED("mcount subcommand");
+}
--
2.31.1