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From:   Matt Helsley <mhelsley@vmware.com>
To:     <linux-kernel@vger.kernel.org>
CC:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Julien Thierry <jthierry@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Matt Helsley <mhelsley@vmware.com>
Subject: [RFC][PATCH 12/36] objtool: mcount: Use libelf for section header names
Date:   Fri, 10 Apr 2020 12:35:35 -0700
Message-ID: <f48713a3beab412085c7a1ec2a03fd0476794cbd.1586468801.git.mhelsley@vmware.com>
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Rather than passing in the string table contents as a parameter,
pass in the section index of the string table and rely on libelf
string table accessor functions to look up section names.

Note that modifying the string table with libelf will come later
so append_func() is unchanged.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
---
 tools/objtool/elf.c          |  3 +-
 tools/objtool/elf.h          |  1 +
 tools/objtool/recordmcount.c |  2 +-
 tools/objtool/recordmcount.h | 89 ++++++++++++++----------------------
 4 files changed, 37 insertions(+), 58 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 88ce3efa394c..4528d2669ac2 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -122,8 +122,7 @@ struct section *find_section_by_name(struct elf *elf, const char *name)
 	return NULL;
 }
 
-static struct section *find_section_by_index(struct elf *elf,
-					     unsigned int idx)
+struct section *find_section_by_index(struct elf *elf, unsigned int idx)
 {
 	struct section *sec;
 
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index 5ad29bb84692..317da07ee10d 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -116,6 +116,7 @@ static inline u32 rela_hash(struct rela *rela)
 
 struct elf *elf_read(const char *name, int flags);
 struct section *find_section_by_name(struct elf *elf, const char *name);
+struct section *find_section_by_index(struct elf *elf, unsigned int idx);
 struct symbol *find_func_by_offset(struct section *sec, unsigned long offset);
 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
 struct symbol *find_symbol_by_name(struct elf *elf, const char *name);
diff --git a/tools/objtool/recordmcount.c b/tools/objtool/recordmcount.c
index df16783434ae..e69d2cccce2d 100644
--- a/tools/objtool/recordmcount.c
+++ b/tools/objtool/recordmcount.c
@@ -177,7 +177,7 @@ static void *mmap_file(char const *fname)
 	file_updated = 0;
 	sb.st_size = 0;
 
-	lf = elf_read(fname, O_RDONLY);
+	lf = elf_read(fname, O_RDWR);
 	if (!lf) {
 		perror(fname);
 		return NULL;
diff --git a/tools/objtool/recordmcount.h b/tools/objtool/recordmcount.h
index 3250a461895d..b487308992ce 100644
--- a/tools/objtool/recordmcount.h
+++ b/tools/objtool/recordmcount.h
@@ -25,7 +25,6 @@
 #undef sift_rel_mcount
 #undef nop_mcount
 #undef find_secsym_ndx
-#undef __has_rel_mcount
 #undef has_rel_mcount
 #undef tot_relsize
 #undef get_mcountsym
@@ -55,7 +54,6 @@
 # define sift_rel_mcount	sift64_rel_mcount
 # define nop_mcount		nop_mcount_64
 # define find_secsym_ndx	find64_secsym_ndx
-# define __has_rel_mcount	__has64_rel_mcount
 # define has_rel_mcount		has64_rel_mcount
 # define tot_relsize		tot64_relsize
 # define get_sym_str_and_relp	get_sym_str_and_relp_64
@@ -88,7 +86,6 @@
 # define sift_rel_mcount	sift32_rel_mcount
 # define nop_mcount		nop_mcount_32
 # define find_secsym_ndx	find32_secsym_ndx
-# define __has_rel_mcount	__has32_rel_mcount
 # define has_rel_mcount		has32_rel_mcount
 # define tot_relsize		tot32_relsize
 # define get_sym_str_and_relp	get_sym_str_and_relp_32
@@ -197,6 +194,7 @@ static int append_func(Elf_Ehdr *const ehdr,
 
 	shstr->sh_size = _w(t);
 	shstr->sh_offset = _w(sb.st_size);
+
 	t += sb.st_size;
 	t += (_align & -t);  /* word-byte align */
 	new_e_shoff = t;
@@ -260,7 +258,7 @@ static int append_func(Elf_Ehdr *const ehdr,
 		return -1;
 	if (uwrite(ehdr, sizeof(*ehdr)) < 0)
 		return -1;
-	return 0;
+	return elf_write(lf);
 }
 
 static unsigned get_mcountsym(Elf_Sym const *const sym0,
@@ -285,7 +283,7 @@ static unsigned get_mcountsym(Elf_Sym const *const sym0,
 	return mcountsym;
 }
 
-static void get_sym_str_and_relp(GElf_Shdr const *const relhdr,
+static void get_sym_str_and_relp(const struct section * const rels,
 				 Elf_Ehdr const *const ehdr,
 				 Elf_Sym const **sym0,
 				 char const **str0,
@@ -293,10 +291,10 @@ static void get_sym_str_and_relp(GElf_Shdr const *const relhdr,
 {
 	Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
 		+ (void *)ehdr);
-	unsigned const symsec_sh_link = relhdr->sh_link;
+	unsigned const symsec_sh_link = rels->sh.sh_link;
 	Elf_Shdr const *const symsec = &shdr0[symsec_sh_link];
 	Elf_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
-	Elf_Rel const *const rel0 = (Elf_Rel const *)(relhdr->sh_offset
+	Elf_Rel const *const rel0 = (Elf_Rel const *)(rels->sh.sh_offset
 		+ (void *)ehdr);
 
 	*sym0 = (Elf_Sym const *)(_w(symsec->sh_offset)
@@ -316,7 +314,7 @@ static void get_sym_str_and_relp(GElf_Shdr const *const relhdr,
 static uint_t *sift_rel_mcount(uint_t *mlocp,
 			       unsigned const offbase,
 			       Elf_Rel **const mrelpp,
-			       GElf_Shdr const *const relhdr,
+			       const struct section * const rels,
 			       Elf_Ehdr const *const ehdr,
 			       unsigned const recsym_index,
 			       uint_t const recval,
@@ -327,12 +325,12 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
 	Elf_Sym const *sym0;
 	char const *str0;
 	Elf_Rel const *relp;
-	unsigned int rel_entsize = relhdr->sh_entsize;
-	unsigned const nrel = relhdr->sh_size / rel_entsize;
+	unsigned int rel_entsize = rels->sh.sh_entsize;
+	unsigned const nrel = rels->sh.sh_size / rel_entsize;
 	unsigned mcountsym = 0;
 	unsigned t;
 
-	get_sym_str_and_relp(relhdr, ehdr, &sym0, &str0, &relp);
+	get_sym_str_and_relp(rels, ehdr, &sym0, &str0, &relp);
 
 	for (t = nrel; t; --t) {
 		if (!mcountsym)
@@ -364,7 +362,7 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
  * that are not going to be traced. The mcount calls here will be converted
  * into nops.
  */
-static int nop_mcount(GElf_Shdr const *const relhdr,
+static int nop_mcount(const struct section * const rels,
 		      Elf_Ehdr const *const ehdr,
 		      const char *const txtname)
 {
@@ -373,14 +371,14 @@ static int nop_mcount(GElf_Shdr const *const relhdr,
 	Elf_Sym const *sym0;
 	char const *str0;
 	Elf_Rel const *relp;
-	Elf_Shdr const *const shdr = &shdr0[relhdr->sh_info];
-	unsigned int rel_entsize = relhdr->sh_entsize;
-	unsigned const nrel = relhdr->sh_size / rel_entsize;
+	Elf_Shdr const *const shdr = &shdr0[rels->sh.sh_info];
+	unsigned rel_entsize = rels->sh.sh_entsize;
+	unsigned const nrel = rels->sh.sh_size / rel_entsize;
 	unsigned mcountsym = 0;
 	unsigned t;
 	int once = 0;
 
-	get_sym_str_and_relp(relhdr, ehdr, &sym0, &str0, &relp);
+	get_sym_str_and_relp(rels, ehdr, &sym0, &str0, &relp);
 
 	for (t = nrel; t; --t) {
 		int ret = -1;
@@ -463,40 +461,27 @@ static int find_secsym_ndx(unsigned const txtndx,
 	return -1;
 }
 
-/* Evade ISO C restriction: no declaration after statement in has_rel_mcount. */
-static char const * __has_rel_mcount(GElf_Shdr const *const relhdr, /* reltype */
-				     Elf_Shdr const *const shdr0,
-				     char const *const shstrtab)
+static char const *has_rel_mcount(const struct section * const rels)
 {
-	/* .sh_info depends on .sh_type == SHT_REL[,A] */
-	Elf_Shdr const *const txthdr = &shdr0[relhdr->sh_info];
-	char const *const txtname = &shstrtab[w(txthdr->sh_name)];
-
-	if (w(txthdr->sh_type) != SHT_PROGBITS ||
-	    !(_w(txthdr->sh_flags) & SHF_EXECINSTR))
+	const struct section *txts;
+	if (rels->sh.sh_type != SHT_REL && rels->sh.sh_type != SHT_RELA)
 		return NULL;
-	return txtname;
-}
-
-static char const *has_rel_mcount(GElf_Shdr const *const relhdr,
-				  Elf_Shdr const *const shdr0,
-				  char const *const shstrtab)
-{
-	if (relhdr->sh_type != SHT_REL && relhdr->sh_type != SHT_RELA)
+	txts = find_section_by_index(lf, rels->sh.sh_info);
+	if ((txts->sh.sh_type != SHT_PROGBITS) ||
+	    !(txts->sh.sh_flags & SHF_EXECINSTR))
 		return NULL;
-	return __has_rel_mcount(relhdr, shdr0, shstrtab);
+	return txts->name;
 }
 
 
-static unsigned tot_relsize(Elf_Shdr const *const shdr0,
-			    const char *const shstrtab)
+static unsigned tot_relsize(void)
 {
-	struct section *sec;
+	const struct section *sec;
 	unsigned totrelsz = 0;
 	char const *txtname;
 
 	list_for_each_entry(sec, &lf->sections, list) {
-		txtname = has_rel_mcount(&sec->sh, shdr0, shstrtab);
+		txtname = has_rel_mcount(sec);
 		if (txtname && is_mcounted_section_name(txtname))
 			totrelsz += sec->sh.sh_size;
 	}
@@ -510,11 +495,6 @@ static int do_func(Elf_Ehdr *const ehdr,
 {
 	Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
 		+ (void *)ehdr);
-	Elf_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
-	char const *const shstrtab = (char const *)(_w(shstr->sh_offset)
-		+ (void *)ehdr);
-
-	GElf_Shdr const *relhdr;
 
 	/* Upper bound on space: assume all relevant relocs are for mcount. */
 	unsigned       totrelsz;
@@ -528,14 +508,14 @@ static int do_func(Elf_Ehdr *const ehdr,
 	unsigned rel_entsize = 0;
 	unsigned symsec_sh_link = 0;
 
-	struct section *sec;
+	const struct section *sec;
 
 	int result = 0;
 
 	if (find_section_by_name(lf, "__mcount_loc") != NULL)
 		return 0;
 
-	totrelsz = tot_relsize(shdr0, shstrtab);
+	totrelsz = tot_relsize();
 	if (totrelsz == 0)
 		return 0;
 	mrel0 = umalloc(totrelsz);
@@ -554,38 +534,37 @@ static int do_func(Elf_Ehdr *const ehdr,
 	list_for_each_entry(sec, &lf->sections, list) {
 		char const *txtname;
 
-		relhdr = &sec->sh;
-		txtname = has_rel_mcount(relhdr, shdr0,
-			shstrtab);
+		txtname = has_rel_mcount(sec);
 		if (txtname && is_mcounted_section_name(txtname)) {
 			unsigned int recsym;
 			uint_t recval = 0;
 
-			symsec_sh_link = relhdr->sh_link;
-			result = find_secsym_ndx(relhdr->sh_info, txtname,
+			symsec_sh_link = sec->sh.sh_link;
+			result = find_secsym_ndx(sec->sh.sh_info, txtname,
 						&recval, &recsym,
 						&shdr0[symsec_sh_link],
 						ehdr);
 			if (result)
 				goto out;
 
-			rel_entsize = relhdr->sh_entsize;
+			rel_entsize = sec->sh.sh_entsize;
 			mlocp = sift_rel_mcount(mlocp,
 				(void *)mlocp - (void *)mloc0, &mrelp,
-				relhdr, ehdr, recsym, recval, reltype);
+				sec, ehdr, recsym, recval, reltype);
 		} else if (txtname && (warn_on_notrace_sect || make_nop)) {
 			/*
 			 * This section is ignored by ftrace, but still
 			 * has mcount calls. Convert them to nops now.
 			 */
-			if (nop_mcount(relhdr, ehdr, txtname) < 0) {
+			if (nop_mcount(sec, ehdr, txtname) < 0) {
 				result = -1;
 				goto out;
 			}
 		}
 	}
 	if (!result && mloc0 != mlocp)
-		result = append_func(ehdr, shstr, mloc0, mlocp, mrel0, mrelp,
+		result = append_func(ehdr, &shdr0[w2(ehdr->e_shstrndx)],
+				     mloc0, mlocp, mrel0, mrelp,
 				     rel_entsize, symsec_sh_link);
 out:
 	free(mrel0);
-- 
2.20.1