[RFC][PATCH v4 27/32] objtool: mcount: Generic location and relocation table types

From: Matt Helsley <mhelsley@vmware.com>
To: <linux-kernel@vger.kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Sami Tolvanen <samitolvanen@google.com>,
	Julien Thierry <jthierry@redhat.com>,
	Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
	Matt Helsley <mhelsley@vmware.com>
Subject: [RFC][PATCH v4 27/32] objtool: mcount: Generic location and relocation table types
Date: Tue, 2 Jun 2020 12:50:20 -0700	[thread overview]
Message-ID: <311ccd169cec877d0c1993772818f0e5cdf11dc4.1591125127.git.mhelsley@vmware.com> (raw)
In-Reply-To: <cover.1591125127.git.mhelsley@vmware.com>

Rather than building the exact ELF section data we need and
avoiding libelf's conversion step, use more GElf types
and then libelf's elfxx_xlatetof() functions to convert
the mcount locations (GElf_Addr) and associated relocations.

This converts sift_rel_mcount() so that it doesn't use the
recordmcount wrapper. The next patch will move it out of the
wrapper.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
---
 tools/objtool/recordmcount.c |  44 +++----------
 tools/objtool/recordmcount.h | 120 ++++++++++++++---------------------
 2 files changed, 59 insertions(+), 105 deletions(-)

diff --git a/tools/objtool/recordmcount.c b/tools/objtool/recordmcount.c
index 06a8f8ddefa7..ef3c360a3db9 100644
--- a/tools/objtool/recordmcount.c
+++ b/tools/objtool/recordmcount.c
@@ -210,7 +210,7 @@ static int is_mcounted_section_name(char const *const txtname)
 		strcmp(".cpuidle.text", txtname) == 0;
 }
 
-static unsigned get_mcountsym(struct reloc *reloc)
+static unsigned int get_mcount_sym_info(struct reloc *reloc)
 {
 	struct symbol *sym = reloc->sym;
 	char const *symname = sym->name;
@@ -321,16 +321,16 @@ static int nop_mcount(struct section * const rels,
 {
 	struct reloc *reloc;
 	struct section *txts = find_section_by_index(lf, rels->sh.sh_info);
-	unsigned mcountsym = 0;
+	unsigned int mcount_sym_info = 0;
 	int once = 0;
 
 	list_for_each_entry(reloc, &rels->reloc_list, list) {
 		int ret = -1;
 
-		if (!mcountsym)
-			mcountsym = get_mcountsym(reloc);
+		if (!mcount_sym_info)
+			mcount_sym_info = get_mcount_sym_info(reloc);
 
-		if (mcountsym == GELF_R_INFO(reloc->sym->idx, reloc->type) && !is_fake_mcount(reloc)) {
+		if (mcount_sym_info == GELF_R_INFO(reloc->sym->idx, reloc->type) && !is_fake_mcount(reloc)) {
 			if (make_nop) {
 				ret = make_nop(txts, reloc->offset);
 				if (ret < 0)
@@ -391,6 +391,9 @@ static unsigned tot_relsize(unsigned int *rel_entsize)
  */
 static int mcount_adjust = 0;
 
+/* Size of an entry in __mcount_loc; 4 or 8 */
+static size_t loc_size;
+
 /* 32 bit and 64 bit are very similar */
 #include "recordmcount.h"
 #define RECORD_MCOUNT_64
@@ -408,34 +411,6 @@ static int arm_is_fake_mcount(struct reloc const *rp)
 	return 1;
 }
 
-/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
- * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
- * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
- * to imply the order of the members; the spec does not say so.
- *	typedef unsigned char Elf64_Byte;
- * fails on MIPS64 because their <elf.h> already has it!
- */
-
-typedef uint8_t myElf64_Byte;		/* Type for a 8-bit quantity.  */
-
-union mips_r_info {
-	Elf64_Xword r_info;
-	struct {
-		Elf64_Word r_sym;		/* Symbol index.  */
-		myElf64_Byte r_ssym;		/* Special symbol.  */
-		myElf64_Byte r_type3;		/* Third relocation.  */
-		myElf64_Byte r_type2;		/* Second relocation.  */
-		myElf64_Byte r_type;		/* First relocation.  */
-	} r_mips;
-};
-
-static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
-{
-	rp->r_info = ((union mips_r_info){
-		.r_mips = { .r_sym = w(sym), .r_type = type }
-	}).r_info;
-}
-
 static int do_file(char const *const fname)
 {
 	unsigned int reltype = 0;
@@ -551,6 +526,7 @@ static int do_file(char const *const fname)
 			reltype = R_MIPS_32;
 			is_fake_mcount = MIPS_is_fake_mcount;
 		}
+		loc_size = 4;
 		rc = do32(reltype);
 		break;
 	case ELFCLASS64: {
@@ -566,9 +542,9 @@ static int do_file(char const *const fname)
 		}
 		if (lf->ehdr.e_machine == EM_MIPS) {
 			reltype = R_MIPS_64;
-			Elf64_r_info = MIPS64_r_info;
 			is_fake_mcount = MIPS_is_fake_mcount;
 		}
+		loc_size = 8;
 		rc = do64(reltype);
 		break;
 	}
diff --git a/tools/objtool/recordmcount.h b/tools/objtool/recordmcount.h
index de31ff003032..b58f0cc58f76 100644
--- a/tools/objtool/recordmcount.h
+++ b/tools/objtool/recordmcount.h
@@ -19,86 +19,63 @@
  */
 #undef sift_rel_mcount
 #undef do_func
-#undef Elf_Shdr
-#undef Elf_Rel
 #undef Elf_Rela
-#undef ELF_R_INFO
-#undef Elf_r_info
-#undef fn_ELF_R_INFO
-#undef uint_t
-#undef _w
-#undef _size
 
 #ifdef RECORD_MCOUNT_64
 # define sift_rel_mcount	sift64_rel_mcount
 # define do_func		do64
-# define Elf_Rel		Elf64_Rel
 # define Elf_Rela		Elf64_Rela
-# define ELF_R_INFO		ELF64_R_INFO
-# define Elf_r_info		Elf64_r_info
-# define fn_ELF_R_INFO		fn_ELF64_R_INFO
-# define uint_t			uint64_t
-# define _w			w8
-# define _size			8
 #else
 # define sift_rel_mcount	sift32_rel_mcount
 # define do_func		do32
-# define Elf_Rel		Elf32_Rel
 # define Elf_Rela		Elf32_Rela
-# define ELF_R_INFO		ELF32_R_INFO
-# define Elf_r_info		Elf32_r_info
-# define fn_ELF_R_INFO		fn_ELF32_R_INFO
-# define uint_t			uint32_t
-# define _w			w
-# define _size			4
 #endif
 
-static void fn_ELF_R_INFO(Elf_Rel *const rp, unsigned sym, unsigned type)
-{
-	rp->r_info = _w(ELF_R_INFO(sym, type));
-}
-static void (*Elf_r_info)(Elf_Rel *const rp, unsigned sym, unsigned type) = fn_ELF_R_INFO;
-
 /*
  * Look at the relocations in order to find the calls to mcount.
  * Accumulate the section offsets that are found, and their relocation info,
  * onto the end of the existing arrays.
  */
-static uint_t *sift_rel_mcount(uint_t *mlocp,
-			       unsigned const offbase,
-			       Elf_Rel **const mrelpp,
+static void sift_rel_mcount(GElf_Addr **mlocpp,
+			       GElf_Sxword *r_offsetp,
+			       void **const mrelpp,
 			       const struct section * const rels,
 			       unsigned const recsym_index,
 			       unsigned long const recval,
-			       unsigned const reltype)
+			       unsigned const reltype,
+			       bool is_rela)
 {
-	uint_t *const mloc0 = mlocp;
-	Elf_Rel *mrelp = *mrelpp;
-	unsigned int rel_entsize = rels->sh.sh_entsize;
-	unsigned mcountsym = 0;
+	GElf_Rel *mrelp = *mrelpp;
+	GElf_Rela *mrelap = *mrelpp;
+	unsigned int mcount_sym_info = 0;
 	struct reloc *reloc;
 
 	list_for_each_entry(reloc, &rels->reloc_list, list) {
-		if (!mcountsym)
-			mcountsym = get_mcountsym(reloc);
-
-		if (mcountsym == GELF_R_INFO(reloc->sym->idx, reloc->type) && !is_fake_mcount(reloc)) {
-			uint_t const addend =
-				_w(reloc->offset - recval + mcount_adjust);
-			mrelp->r_offset = _w(offbase
-				+ ((void *)mlocp - (void *)mloc0));
-			Elf_r_info(mrelp, recsym_index, reltype);
-			if (rel_entsize == sizeof(Elf_Rela)) {
-				((Elf_Rela *)mrelp)->r_addend = addend;
-				*mlocp++ = 0;
-			} else
-				*mlocp++ = addend;
-
-			mrelp = (Elf_Rel *)(rel_entsize + (void *)mrelp);
+		unsigned long addend;
+
+		if (!mcount_sym_info)
+			mcount_sym_info = get_mcount_sym_info(reloc);
+
+		if (mcount_sym_info != GELF_R_INFO(reloc->sym->idx, reloc->type) || is_fake_mcount(reloc))
+			continue;
+
+		addend = reloc->offset - recval + mcount_adjust;
+		if (is_rela) {
+			mrelap->r_offset = *r_offsetp;
+			mrelap->r_info = GELF_R_INFO(recsym_index, reltype);
+			mrelap->r_addend = addend;
+			mrelap++;
+			**mlocpp = 0;
+		} else {
+			mrelp->r_offset = *r_offsetp;
+			mrelp->r_info = GELF_R_INFO(recsym_index, reltype);
+			mrelp++;
+			**mlocpp = addend;
 		}
+		(*mlocpp)++;
+		r_offsetp += loc_size;
 	}
-	*mrelpp = mrelp;
-	return mlocp;
+	*mrelpp = is_rela ? (void *)mrelap : (void *)mrelp;
 }
 
 
@@ -108,11 +85,12 @@ static int do_func(unsigned const reltype)
 	/* Upper bound on space: assume all relevant relocs are for mcount. */
 	unsigned       totrelsz;
 
-	Elf_Rel *      mrel0;
-	Elf_Rel *      mrelp;
+	void *mrel0;
+	void *mrelp;
 
-	uint_t *      mloc0;
-	uint_t *      mlocp;
+	GElf_Addr *mloc0;
+	GElf_Addr *mlocp;
+	GElf_Sxword r_offset = 0;
 
 	unsigned int rel_entsize = 0;
 
@@ -149,25 +127,28 @@ static int do_func(unsigned const reltype)
 			:  ".rel__mcount_loc";
 
 	/* add section: __mcount_loc */
-	mlocs = elf_create_section(lf, mc_name + (is_rela ? 1 : 0) + strlen(".rel"), _size, 0);
+	mlocs = elf_create_section(lf, mc_name + (is_rela ? 1 : 0) + strlen(".rel"), sizeof(*mloc0), 0);
 	if (!mlocs)
 		goto out;
 
 	mlocs->sh.sh_link = 0;
 	mlocs->sh.sh_info = 0;
-	mlocs->sh.sh_addralign = _size;
+	mlocs->sh.sh_addralign = 8;
+	mlocs->data->d_buf = mloc0;
+	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);
 	if (!mrels)
 		goto out;
-	mrels->sh.sh_type = is_rela
-				? SHT_RELA
-				: SHT_REL;
+	/* Like elf_create_rela_section() without the name bits */
+	mrels->sh.sh_type = is_rela ? SHT_RELA : SHT_REL;
 	mrels->sh.sh_flags = 0;
 	mrels->sh.sh_link = find_section_by_name(lf, ".symtab")->idx;
 	mrels->sh.sh_info = old_shnum;
-	mrels->sh.sh_addralign = _size;
+	mrels->sh.sh_addralign = 8;
+	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;
@@ -181,9 +162,8 @@ static int do_func(unsigned const reltype)
 						txtname, &recval, &recsym))
 				goto out;
 
-			mlocp = sift_rel_mcount(mlocp,
-				(void *)mlocp - (void *)mloc0, &mrelp,
-				sec, recsym, (uint_t)recval, reltype);
+			sift_rel_mcount(&mlocp, &r_offset, &mrelp, sec,
+				recsym, recval, reltype, is_rela);
 		} else if (txtname && (warn_on_notrace_sect || make_nop)) {
 			/*
 			 * This section is ignored by ftrace, but still
@@ -195,16 +175,14 @@ static int do_func(unsigned const reltype)
 	}
 
 	if (mloc0 != mlocp) {
-		/* Update the section sizes */
+		/* Update the section size and Elf_Data size */
 		mlocs->sh.sh_size = (void *)mlocp - (void *)mloc0;
 		mlocs->len = mlocs->sh.sh_size;
 		mlocs->data->d_size = mlocs->len;
-		mlocs->data->d_buf = mloc0;
 
-		mrels->sh.sh_size = (void *)mrelp - (void *)mrel0;
+		mrels->sh.sh_size = mrelp - mrel0;
 		mrels->len = mrels->sh.sh_size;
 		mrels->data->d_size = mrels->len;
-		mrels->data->d_buf = mrel0;
 
 		/* overwrite the ELF file */
 		result = elf_write(lf);
-- 
2.20.1

