linux-kernel - [RFC][PATCH v5 31/51] objtool: mcount: Use objtool relocation section

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Message-ID: <19fca156c1171bb723ea98f911b4f0e38ec4d8f0.1592510545.git.mhelsley@vmware.com>
Date:   Thu, 18 Jun 2020 13:38:17 -0700
From:   Matt Helsley <mhelsley@...are.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julien Thierry <jthierry@...hat.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Matt Helsley <mhelsley@...are.com>
Subject: [RFC][PATCH v5 31/51] objtool: mcount: Use objtool relocation section

Now that we add an initially-empty relocation section and share
the libelf data buffer from the beginning, we can safely use
objtools elf_create_reloc_section() function to simplify the
code further -- use the anticipated base section name, avoid
the need to set sh_info, etc. The only remaining difference
between this and the old recordmcount code is we didn't set
SHF_INFO_LINK so we clear the sh_flags as before.

Signed-off-by: Matt Helsley <mhelsley@...are.com>
---
 tools/objtool/recordmcount.h | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/tools/objtool/recordmcount.h b/tools/objtool/recordmcount.h
index 1d11dfc40d09..fc6346a7eaf5 100644
--- a/tools/objtool/recordmcount.h
+++ b/tools/objtool/recordmcount.h
@@ -92,7 +92,7 @@ static int do_func(unsigned const reltype)
 	GElf_Sxword r_offset = 0;
 
 	struct section *sec, *mlocs, *mrels;
-	const char *mc_name;
+	const char * const mc_name =  "__mcount_loc";
 
 	unsigned int rel_entsize = 0;
 	int result = -1;
@@ -119,12 +119,9 @@ static int do_func(unsigned const reltype)
 	}
 
 	is_rela = (sizeof(Elf_Rela) == rel_entsize);
-	mc_name = is_rela
-			? ".rela__mcount_loc"
-			:  ".rel__mcount_loc";
 
 	/* add section: __mcount_loc */
-	mlocs = elf_create_section(lf, mc_name + (is_rela ? 1 : 0) + strlen(".rel"), sizeof(*mloc0), 0);
+	mlocs = elf_create_section(lf, mc_name, sizeof(*mloc0), 0);
 	if (!mlocs)
 		goto out;
 	mlocs->sh.sh_link = 0;
@@ -134,17 +131,12 @@ static int do_func(unsigned const reltype)
 	mlocs->data->d_type = ELF_T_ADDR; /* elf_xlatetof() conversion */
 
 	/* add section .rel[a]__mcount_loc */
-	mrels = elf_create_section(lf, mc_name, rel_entsize, 0);
+	mrels = elf_create_reloc_section(lf, mlocs,
+					 is_rela ? SHT_RELA : SHT_REL);
 	if (!mrels)
 		goto out;
-	/* Like elf_create_rela_section() without the name bits */
-	mrels->sh.sh_type = is_rela ? SHT_RELA : SHT_REL;
-	mrels->sh.sh_flags = 0; /* clear SHF_ALLOC */
-	mrels->sh.sh_link = find_section_by_name(lf, ".symtab")->idx;
-	mrels->sh.sh_info = mlocs->idx;
-	mrels->sh.sh_addralign = 8;
+	mrels->sh.sh_flags = 0; /* clear SHF_INFO_LINK */
 	mrels->data->d_buf = mrel0;
-	mrels->data->d_type = is_rela ? ELF_T_RELA : ELF_T_REL; /* elf_xlatetof() conversion */
 
 	list_for_each_entry(sec, &lf->sections, list) {
 		char const *txtname;
-- 
2.20.1