[PATCH v4 11/16] objtool: Add --mnop as an option to --mcount

[Sathvika Vasireddy]

Some architectures (powerpc) may not support ftrace locations being nop'ed
out at build time. Introduce CONFIG_HAVE_OBJTOOL_NOP_MCOUNT for objtool, as
a means for architectures to enable nop'ing of ftrace locations. Add --mnop
as an option to objtool --mcount, to indicate support for the same.

Also, make sure that --mnop can be passed as an option to objtool only when
--mcount is passed.

Signed-off-by: Sathvika Vasireddy <sv at linux.ibm.com>
---
 Makefile                                |  4 +++-
 arch/x86/Kconfig                        |  1 +
 kernel/trace/Kconfig                    |  7 +++++++
 scripts/Makefile.lib                    |  1 +
 tools/objtool/builtin-check.c           | 14 ++++++++++++++
 tools/objtool/check.c                   | 19 ++++++++++---------
 tools/objtool/include/objtool/builtin.h |  1 +
 7 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index a5e9d9388649..b2230ad14748 100644
--- a/Makefile
+++ b/Makefile
@@ -857,7 +857,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
   endif
 endif
 ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
-  CC_FLAGS_USING	+= -DCC_USING_NOP_MCOUNT
+  ifdef CONFIG_HAVE_OBJTOOL_NOP_MCOUNT
+    CC_FLAGS_USING	+= -DCC_USING_NOP_MCOUNT
+  endif
 endif
 ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
   ifdef CONFIG_HAVE_C_RECORDMCOUNT
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f9920f1341c8..2a79a05c4402 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -189,6 +189,7 @@ config X86
 	select HAVE_CONTEXT_TRACKING_USER_OFFSTACK	if HAVE_CONTEXT_TRACKING_USER
 	select HAVE_C_RECORDMCOUNT
 	select HAVE_OBJTOOL_MCOUNT		if HAVE_OBJTOOL
+	select HAVE_OBJTOOL_NOP_MCOUNT		if HAVE_OBJTOOL_MCOUNT
 	select HAVE_BUILDTIME_MCOUNT_SORT
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 1052126bdca2..9c696cb24756 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -76,6 +76,13 @@ config HAVE_OBJTOOL_MCOUNT
 	help
 	  Arch supports objtool --mcount
 
+config HAVE_OBJTOOL_NOP_MCOUNT
+	bool
+	help
+	  Arch supports the objtool options --mcount with --mnop.
+	  An architecture can select this if it wants to enable nop'ing
+	  of ftrace locations.
+
 config HAVE_C_RECORDMCOUNT
 	bool
 	help
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 3fb6a99e78c4..ce14e3b8577f 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -234,6 +234,7 @@ objtool_args =								\
 	$(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=noinstr)		\
 	$(if $(CONFIG_X86_KERNEL_IBT), --ibt)				\
 	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
+	$(if $(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT), --mnop)                 \
 	$(if $(CONFIG_UNWINDER_ORC), --orc)				\
 	$(if $(CONFIG_RETPOLINE), --retpoline)				\
 	$(if $(CONFIG_RETHUNK), --rethunk)				\
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 24fbe803a0d3..9bd347d3c244 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -82,6 +82,7 @@ const struct option check_options[] = {
 	OPT_BOOLEAN(0, "dry-run", &opts.dryrun, "don't write modifications"),
 	OPT_BOOLEAN(0, "link", &opts.link, "object is a linked object"),
 	OPT_BOOLEAN(0, "module", &opts.module, "object is part of a kernel module"),
+	OPT_BOOLEAN(0, "mnop", &opts.mnop, "nop out mcount call sites"),
 	OPT_BOOLEAN(0, "no-unreachable", &opts.no_unreachable, "skip 'unreachable instruction' warnings"),
 	OPT_BOOLEAN(0, "sec-address", &opts.sec_address, "print section addresses in warnings"),
 	OPT_BOOLEAN(0, "stats", &opts.stats, "print statistics"),
@@ -150,6 +151,16 @@ static bool opts_valid(void)
 	return false;
 }
 
+static bool mnop_opts_valid(void)
+{
+	if (opts.mnop && !opts.mcount) {
+		ERROR("--mnop requires --mcount");
+		return false;
+	}
+
+	return true;
+}
+
 static bool link_opts_valid(struct objtool_file *file)
 {
 	if (opts.link)
@@ -198,6 +209,9 @@ int objtool_run(int argc, const char **argv)
 	if (!file)
 		return 1;
 
+	if (!mnop_opts_valid())
+		return 1;
+
 	if (!link_opts_valid(file))
 		return 1;
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 738de23cb9e8..35827e6c6df9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1233,17 +1233,18 @@ static void annotate_call_site(struct objtool_file *file,
 	if (opts.mcount && sym->fentry) {
 		if (sibling)
 			WARN_FUNC("Tail call to __fentry__ !?!?", insn->sec, insn->offset);
+		if (opts.mnop) {
+			if (reloc) {
+				reloc->type = R_NONE;
+				elf_write_reloc(file->elf, reloc);
+			}
 
-		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));
+			elf_write_insn(file->elf, insn->sec,
+				       insn->offset, insn->len,
+				       arch_nop_insn(insn->len));
 
-		insn->type = INSN_NOP;
+			insn->type = INSN_NOP;
+		}
 
 		list_add_tail(&insn->call_node, &file->mcount_loc_list);
 		return;
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 42a52f1a0add..0785707c5a92 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -31,6 +31,7 @@ struct opts {
 	bool backup;
 	bool dryrun;
 	bool link;
+	bool mnop;
 	bool module;
 	bool no_unreachable;
 	bool sec_address;
-- 
2.31.1