[RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool

Peter Zijlstra
2020-06-25T20:03:14Z

On Thu, Jun 25, 2020 at 09:15:03AM -0700, Sami Tolvanen wrote:
> On Thu, Jun 25, 2020 at 09:45:30AM +0200, Peter Zijlstra wrote:

> > At least for x86_64 I can do a really quick take for a recordmcount pass
> > in objtool, but I suppose you also need this for ARM64 ?
>
> Sure, sounds good. arm64 uses -fpatchable-function-entry with clang, so we
> don't need recordmcount there.

This is on top of my local pile:

git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git master

which notably includes the static_call series.

Not boot tested, but it generates the required sections and they look
more or less as expected, ymmv.

---
arch/x86/Kconfig | 1 -
scripts/Makefile.build | 3 ++
scripts/link-vmlinux.sh | 2 +-
tools/objtool/builtin-check.c | 9 ++---
tools/objtool/builtin.h | 2 +-
tools/objtool/check.c | 81 +++++++++++++++++++++++++++++++++++++++++++
tools/objtool/check.h | 1 +
tools/objtool/objtool.h | 1 +
8 files changed, 91 insertions(+), 9 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a291823f3f26..189575c12434 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -174,7 +174,6 @@ config X86
select HAVE_EXIT_THREAD
select HAVE_FAST_GUP
select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE
- select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_TRACER
select HAVE_GCC_PLUGINS
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 2e8810b7e5ed..c774befc57da 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -227,6 +227,9 @@ endif
ifdef CONFIG_X86_SMAP
objtool_args += --uaccess
endif
+ifdef CONFIG_DYNAMIC_FTRACE
+ objtool_args += --mcount
+endif

# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 92dd745906f4..00c6e4f28a1a 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -60,7 +60,7 @@ objtool_link()
local objtoolopt;

if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then
- objtoolopt="check"
+ objtoolopt="check --vmlinux"
if [ -z "${CONFIG_FRAME_POINTER}" ]; then
objtoolopt="${objtoolopt} --no-fp"
fi
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 4896c5a89702..a6c3a3fba67d 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -18,7 +18,7 @@
#include "builtin.h"
#include "objtool.h"

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

static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -36,12 +36,13 @@ const struct option check_options[] = {
OPT_BOOLEAN('d', "duplicate", &validate_dup, "duplicate validation for vmlinux.o"),
OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),
OPT_BOOLEAN('F', "fpu", &fpu, "validate FPU context"),
+ OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),
OPT_END(),
};

int cmd_check(int argc, const char **argv)
{
- const char *objname, *s;
+ const char *objname;

argc = parse_options(argc, argv, check_options, check_usage, 0);

@@ -50,9 +51,5 @@ int cmd_check(int argc, const char **argv)

objname = argv[0];

- s = strstr(objname, "vmlinux.o");
- if (s && !s[9])
- vmlinux = true;
-
return check(objname, false);
}
diff --git a/tools/objtool/builtin.h b/tools/objtool/builtin.h
index 7158e09d4cc9..b51d883ec245 100644
--- a/tools/objtool/builtin.h
+++ b/tools/objtool/builtin.h
@@ -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, fpu;
+extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux, fpu, mcount;

extern int cmd_check(int argc, const char **argv);
extern int cmd_orc(int argc, const char **argv);
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6647a8d1545b..ee99566bdae9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -533,6 +533,65 @@ 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.
*/
@@ -892,6 +951,22 @@ 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.
@@ -3004,6 +3079,7 @@ int check(const char *_objname, bool orc)
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;
@@ -3056,6 +3132,11 @@ int check(const char *_objname, bool orc)
goto out;
warnings += ret;

+ ret = create_mcount_loc_sections(&file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+
if (orc) {
ret = create_orc(&file);
if (ret < 0)
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index cd95fca0d237..01f11b5da5dd 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -24,6 +24,7 @@ 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;
diff --git a/tools/objtool/objtool.h b/tools/objtool/objtool.h
index 9a7cd0b88bd8..f604b22d22cc 100644
--- a/tools/objtool/objtool.h
+++ b/tools/objtool/objtool.h
@@ -17,6 +17,7 @@ struct objtool_file {
struct list_head insn_list;
DECLARE_HASHTABLE(insn_hash, 20);
struct list_head static_call_list;
+ struct list_head mcount_loc_list;
bool ignore_unreachables, c_file, hints, rodata;
};