diff mbox series

[v2,05/28] objtool: Add a pass for generating __mcount_loc

Message ID 20200903203053.3411268-6-samitolvanen@google.com
State New, archived
Headers show
Series Add support for Clang LTO | expand

Commit Message

Sami Tolvanen Sept. 3, 2020, 8:30 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>
---
 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

Kees Cook Sept. 3, 2020, 9:51 p.m. UTC | #1
On Thu, Sep 03, 2020 at 01:30:30PM -0700, 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>

Hmm, I'm not sure why this hasn't gotten picked up yet. Is this expected
to go through -tip or something else?

Reviewed-by: Kees Cook <keescook@chromium.org>
Sami Tolvanen Sept. 3, 2020, 10:03 p.m. UTC | #2
On Thu, Sep 3, 2020 at 2:51 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Sep 03, 2020 at 01:30:30PM -0700, 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>
>
> Hmm, I'm not sure why this hasn't gotten picked up yet. Is this expected
> to go through -tip or something else?

Note that I picked up this patch from Peter's original email, to which
I included a link in the commit message, but it wasn't officially
submitted as a patch. However, the previous discussion seems to have
died, so I included the patch in this series, as it cleanly solves the
problem of whitelisting non-call references to __fentry__. I was
hoping for Peter and Steven to comment on how they prefer to proceed
here.

Sami
Peter Zijlstra Sept. 4, 2020, 9:31 a.m. UTC | #3
On Thu, Sep 03, 2020 at 03:03:30PM -0700, Sami Tolvanen wrote:
> On Thu, Sep 3, 2020 at 2:51 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > On Thu, Sep 03, 2020 at 01:30:30PM -0700, 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>
> >
> > Hmm, I'm not sure why this hasn't gotten picked up yet. Is this expected
> > to go through -tip or something else?
> 
> Note that I picked up this patch from Peter's original email, to which
> I included a link in the commit message, but it wasn't officially
> submitted as a patch. However, the previous discussion seems to have
> died, so I included the patch in this series, as it cleanly solves the
> problem of whitelisting non-call references to __fentry__. I was
> hoping for Peter and Steven to comment on how they prefer to proceed
> here.

Right; so I'm obviously fine with this patch and I suppose I can pick it
(and the next) into tip/objtool/core, provided Steve is okay with this
approach.
Kees Cook Sept. 10, 2020, 6:29 p.m. UTC | #4
On Fri, Sep 04, 2020 at 11:31:04AM +0200, peterz@infradead.org wrote:
> On Thu, Sep 03, 2020 at 03:03:30PM -0700, Sami Tolvanen wrote:
> > On Thu, Sep 3, 2020 at 2:51 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > On Thu, Sep 03, 2020 at 01:30:30PM -0700, 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>
> > >
> > > Hmm, I'm not sure why this hasn't gotten picked up yet. Is this expected
> > > to go through -tip or something else?
> > 
> > Note that I picked up this patch from Peter's original email, to which
> > I included a link in the commit message, but it wasn't officially
> > submitted as a patch. However, the previous discussion seems to have
> > died, so I included the patch in this series, as it cleanly solves the
> > problem of whitelisting non-call references to __fentry__. I was
> > hoping for Peter and Steven to comment on how they prefer to proceed
> > here.
> 
> Right; so I'm obviously fine with this patch and I suppose I can pick it
> (and the next) into tip/objtool/core, provided Steve is okay with this
> approach.

Hello Steven-of-the-future-after-4000-emails![1] ;)

Getting your Ack on this would be very welcome, and would unblock a
portion of this series.

Thanks! :)

[1] https://twitter.com/srostedt/status/1303697650592755712
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 e034a8f24f46..6e0b478dc065 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;
 };