linux-kernel - [RFC][PATCH 27/36] objtool: mcount: Use ELF header from objtool

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Date:   Fri, 10 Apr 2020 12:35:50 -0700
From:   Matt Helsley <mhelsley@...are.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Julien Thierry <jthierry@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Matt Helsley <mhelsley@...are.com>
Subject: [RFC][PATCH 27/36] objtool: mcount: Use ELF header from objtool

The ELF header is the very first structure in an ELF file.
Rather than cast it from the file mapping we use the ELF
header extracted via objtool's ELF code.

This should be the last usage of the open-coded mapping of
the ELF file. We will remove the mapping in a later step.

Signed-off-by: Matt Helsley <mhelsley@...are.com>
---
 tools/objtool/recordmcount.c | 37 +++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

diff --git a/tools/objtool/recordmcount.c b/tools/objtool/recordmcount.c
index 6de744aaf4c8..409f0ef82211 100644
--- a/tools/objtool/recordmcount.c
+++ b/tools/objtool/recordmcount.c
@@ -523,21 +523,19 @@ static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 static int do_file(char const *const fname)
 {
 	unsigned int reltype = 0;
-	Elf32_Ehdr *ehdr;
 	int rc = -1;
 
-	ehdr = mmap_file(fname);
-	if (!ehdr)
+	if (!mmap_file(fname))
 		goto out;
 
 	w = w4nat;
 	w2 = w2nat;
 	w8 = w8nat;
-	switch (ehdr->e_ident[EI_DATA]) {
+	switch (lf->ehdr.e_ident[EI_DATA]) {
 		static unsigned int const endian = 1;
 	default:
 		fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
-			ehdr->e_ident[EI_DATA], fname);
+			lf->ehdr.e_ident[EI_DATA], fname);
 		goto out;
 	case ELFDATA2LSB:
 		if (*(unsigned char const *)&endian != 1) {
@@ -566,18 +564,18 @@ static int do_file(char const *const fname)
 		push_bl_mcount_thumb = push_bl_mcount_thumb_be;
 		break;
 	}  /* end switch */
-	if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 ||
-	    w2(ehdr->e_type) != ET_REL ||
-	    ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
+	if (memcmp(ELFMAG, lf->ehdr.e_ident, SELFMAG) != 0 ||
+	    lf->ehdr.e_type != ET_REL ||
+	    lf->ehdr.e_ident[EI_VERSION] != EV_CURRENT) {
 		fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 		goto out;
 	}
 
 	gpfx = '_';
-	switch (w2(ehdr->e_machine)) {
+	switch (lf->ehdr.e_machine) {
 	default:
 		fprintf(stderr, "unrecognized e_machine %u %s\n",
-			w2(ehdr->e_machine), fname);
+			lf->ehdr.e_machine, fname);
 		goto out;
 	case EM_386:
 		reltype = R_386_32;
@@ -618,37 +616,36 @@ static int do_file(char const *const fname)
 		break;
 	}  /* end switch */
 
-	switch (ehdr->e_ident[EI_CLASS]) {
+	switch (lf->ehdr.e_ident[EI_CLASS]) {
 	default:
 		fprintf(stderr, "unrecognized ELF class %d %s\n",
-			ehdr->e_ident[EI_CLASS], fname);
+			lf->ehdr.e_ident[EI_CLASS], fname);
 		goto out;
 	case ELFCLASS32:
-		if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
-		||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
+		if (lf->ehdr.e_ehsize != sizeof(Elf32_Ehdr)
+		||  lf->ehdr.e_shentsize != sizeof(Elf32_Shdr)) {
 			fprintf(stderr,
 				"unrecognized ET_REL file: %s\n", fname);
 			goto out;
 		}
-		if (w2(ehdr->e_machine) == EM_MIPS) {
+		if (lf->ehdr.e_machine == EM_MIPS) {
 			reltype = R_MIPS_32;
 			is_fake_mcount = MIPS_is_fake_mcount;
 		}
 		rc = do32(reltype);
 		break;
 	case ELFCLASS64: {
-		Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
-		if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
-		||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
+		if (lf->ehdr.e_ehsize != sizeof(Elf64_Ehdr)
+		||  lf->ehdr.e_shentsize != sizeof(Elf64_Shdr)) {
 			fprintf(stderr,
 				"unrecognized ET_REL file: %s\n", fname);
 			goto out;
 		}
-		if (w2(ghdr->e_machine) == EM_S390) {
+		if (lf->ehdr.e_machine == EM_S390) {
 			reltype = R_390_64;
 			mcount_adjust_64 = -14;
 		}
-		if (w2(ghdr->e_machine) == EM_MIPS) {
+		if (lf->ehdr.e_machine == EM_MIPS) {
 			reltype = R_MIPS_64;
 			Elf64_r_info = MIPS64_r_info;
 			is_fake_mcount = MIPS_is_fake_mcount;
-- 
2.20.1