linux-kernel - [RFC PATCH 1/1] scripts/recordmcount.{c,pl}: support -ffunction-sections .text.* section names

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Message-Id: <1542745158-25392-2-git-send-email-joe.lawrence@redhat.com>
Date:   Tue, 20 Nov 2018 15:19:18 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: [RFC PATCH 1/1] scripts/recordmcount.{c,pl}: support -ffunction-sections .text.* section names

When building with -ffunction-sections, the compiler will place each
function into its own ELF section, prefixed with ".text".  For example,
a simple test module with functions test_module_do_work() and
test_module_wq_func():

  % objdump --section-headers test_module.o | awk '/\.text/{print $2}'
  .text
  .text.test_module_do_work
  .text.test_module_wq_func
  .init.text
  .exit.text

Adjust the recordmcount scripts to look for ".text" as a section name
prefix.  This will ensure that those functions will be included in the
__mcount_loc relocations:

  % objdump --reloc --section __mcount_loc test_module.o
  OFFSET           TYPE              VALUE
  0000000000000000 R_X86_64_64       .text.test_module_do_work
  0000000000000008 R_X86_64_64       .text.test_module_wq_func
  0000000000000010 R_X86_64_64       .init.text

Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
---
 scripts/recordmcount.c  |  2 +-
 scripts/recordmcount.pl | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 895c40e8679f..a50a2aa963ad 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -397,7 +397,7 @@ static uint32_t w2nat(uint16_t const x)
 static int
 is_mcounted_section_name(char const *const txtname)
 {
-	return strcmp(".text",           txtname) == 0 ||
+	return strncmp(".text",          txtname, 5) == 0 ||
 		strcmp(".init.text",     txtname) == 0 ||
 		strcmp(".ref.text",      txtname) == 0 ||
 		strcmp(".sched.text",    txtname) == 0 ||
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index f599031260d5..68841d01162c 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -142,6 +142,11 @@ my %text_sections = (
      ".text.unlikely" => 1,
 );
 
+# Acceptable section-prefixes to record.
+my %text_section_prefixes = (
+     ".text." => 1,
+);
+
 # Note: we are nice to C-programmers here, thus we skip the '||='-idiom.
 $objdump = 'objdump' if (!$objdump);
 $objcopy = 'objcopy' if (!$objcopy);
@@ -519,6 +524,14 @@ while (<IN>) {
 
 	# Only record text sections that we know are safe
 	$read_function = defined($text_sections{$1});
+	if (!$read_function) {
+	    foreach my $prefix (keys %text_section_prefixes) {
+	        if (substr($1, 0, length $prefix) eq $prefix) {
+	            $read_function = 1;
+	            last;
+	        }
+	    }
+	}
 	# print out any recorded offsets
 	update_funcs();
 
-- 
1.8.3.1