diff mbox series

[v4,04/29] objtool: Add a pass for generating __mcount_loc

Message ID 20200929214631.3516445-5-samitolvanen@google.com
State New, archived
Headers show
Series Add support for Clang LTO | expand

Commit Message

Sami Tolvanen Sept. 29, 2020, 9:46 p.m. UTC
From: Peter Zijlstra <peterz@infradead.org>

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: Peter Zijlstra <peterz@infradead.org>
[Sami: rebased to mainline, dropped config changes, fixed to actually use
       --mcount, and wrote a commit message.]
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 tools/objtool/builtin-check.c |  3 +-
 tools/objtool/builtin.h       |  2 +-
 tools/objtool/check.c         | 83 +++++++++++++++++++++++++++++++++++
 tools/objtool/check.h         |  1 +
 tools/objtool/objtool.h       |  1 +
 5 files changed, 88 insertions(+), 2 deletions(-)

Comments

Miroslav Benes Oct. 1, 2020, 1:17 p.m. UTC | #1
Hi Sami,

On Tue, 29 Sep 2020, Sami Tolvanen wrote:

> From: Peter Zijlstra <peterz@infradead.org>
> 
> 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: Peter Zijlstra <peterz@infradead.org>
> [Sami: rebased to mainline, dropped config changes, fixed to actually use
>        --mcount, and wrote a commit message.]
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>

I am sorry to reply on v4. Should have been sooner.

Julien has been sending patches to make objtool's check functionality 
arch-agnostic as much as possible. So it seems to me that the patch should 
be based on the effort

I also wonder about making 'mcount' command separate from 'check'. Similar 
to what is 'orc' now. But that could be done later.

See tip-tree/objtool/core for both.

Thanks
Miroslav
Peter Zijlstra Oct. 1, 2020, 1:36 p.m. UTC | #2
On Thu, Oct 01, 2020 at 03:17:07PM +0200, Miroslav Benes wrote:

> I also wonder about making 'mcount' command separate from 'check'. Similar 
> to what is 'orc' now. But that could be done later.

I'm not convinced more commands make sense. That only begets us the
problem of having to run multiple commands.
Josh Poimboeuf Oct. 2, 2020, 2:13 p.m. UTC | #3
On Thu, Oct 01, 2020 at 03:36:12PM +0200, Peter Zijlstra wrote:
> On Thu, Oct 01, 2020 at 03:17:07PM +0200, Miroslav Benes wrote:
> 
> > I also wonder about making 'mcount' command separate from 'check'. Similar 
> > to what is 'orc' now. But that could be done later.
> 
> I'm not convinced more commands make sense. That only begets us the
> problem of having to run multiple commands.

Agreed, it gets hairy when we need to combine things.  I think "orc" as
a separate subcommand was a mistake.

We should change to something like

  objtool run [--check] [--orc] [--mcount]
  objtool dump [--orc] [--mcount]
Miroslav Benes Oct. 5, 2020, 7:10 a.m. UTC | #4
On Fri, 2 Oct 2020, Josh Poimboeuf wrote:

> On Thu, Oct 01, 2020 at 03:36:12PM +0200, Peter Zijlstra wrote:
> > On Thu, Oct 01, 2020 at 03:17:07PM +0200, Miroslav Benes wrote:
> > 
> > > I also wonder about making 'mcount' command separate from 'check'. Similar 
> > > to what is 'orc' now. But that could be done later.
> > 
> > I'm not convinced more commands make sense. That only begets us the
> > problem of having to run multiple commands.
> 
> Agreed, it gets hairy when we need to combine things.  I think "orc" as
> a separate subcommand was a mistake.
> 
> We should change to something like
> 
>   objtool run [--check] [--orc] [--mcount]
>   objtool dump [--orc] [--mcount]

Yes, that makes sense.

Miroslav
diff mbox series

Patch

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 7a44174967b5..71595cf4946d 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;
+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(),
 };
 
diff --git a/tools/objtool/builtin.h b/tools/objtool/builtin.h
index 85c979caa367..94565a72b701 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;
+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);
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 90a66891441a..ff0cd4d27d40 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -433,6 +433,65 @@  static int add_dead_ends(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", 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.
  */
@@ -784,6 +843,22 @@  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.
@@ -2791,6 +2866,7 @@  int check(const char *_objname, bool orc)
 
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
+	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;
@@ -2838,6 +2914,13 @@  int check(const char *_objname, bool orc)
 		warnings += ret;
 	}
 
+	if (mcount) {
+		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 061aa96e15d3..b62afd3d970b 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -22,6 +22,7 @@  struct insn_state {
 struct instruction {
 	struct list_head list;
 	struct hlist_node hash;
+	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 528028a66816..427806079540 100644
--- a/tools/objtool/objtool.h
+++ b/tools/objtool/objtool.h
@@ -16,6 +16,7 @@  struct objtool_file {
 	struct elf *elf;
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 20);
+	struct list_head mcount_loc_list;
 	bool ignore_unreachables, c_file, hints, rodata;
 };