linux-kernel - [PATCH 4.9 36/49] trace: Use -mcount-record for dynamic ftrace

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Message-Id: <20210222121027.597696546@linuxfoundation.org>
Date:   Mon, 22 Feb 2021 13:36:34 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Subject: [PATCH 4.9 36/49] trace: Use -mcount-record for dynamic ftrace

From: Andi Kleen <ak@...ux.intel.com>

commit 96f60dfa5819a065bfdd2f2ba0df7d9cbce7f4dd upstream.

gcc 5 supports a new -mcount-record option to generate ftrace
tables directly. This avoids the need to run record_mcount
manually.

Use this option when available.

So far doesn't use -mcount-nop, which also exists now.

This is needed to make ftrace work with LTO because the
normal record-mcount script doesn't run over the link
time output.

It should also improve build times slightly in the general
case.
Link: http://lkml.kernel.org/r/20171127213423.27218-12-andi@firstfloor.org

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 scripts/Makefile.build |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -222,6 +222,11 @@ cmd_modversions_c =								\
 endif
 
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
+# gcc 5 supports generating the mcount tables directly
+ifneq ($(call cc-option,-mrecord-mcount,y),y)
+KBUILD_CFLAGS += -mrecord-mcount
+else
+# else do it all manually
 ifdef BUILD_C_RECORDMCOUNT
 ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
   RECORDMCOUNT_FLAGS = -w
@@ -264,6 +269,7 @@ endif
 ifdef CONFIG_GCOV_KERNEL
 objtool_args += --no-unreachable
 endif
+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