ftrace: Add C version of recordmcount compile time code

Currently, the mcount callers are found with a perl script that does
an objdump on every file in the kernel. This is a C version of that
same code which should increase the performance time of compiling
the kernel with dynamic ftrace enabled.
Signed-off-by: John Reiser <jreiser@bitwagon.com>

[ Updated the code to include .text.unlikely section as well as
  changing the format to follow Linux coding style. ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

scripts/recordmcount.c

+/*
+ * recordmcount.c: construct a table of the locations of calls to 'mcount'
+ * so that ftrace can find them quickly.
+ * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>.  All rights reserved.
+ * Licensed under the GNU General Public License, version 2 (GPLv2).
+ *
+ * Restructured to fit Linux format, as well as other updates:
+ *  Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
+ */
+
+/*
+ * Strategy: alter the .o file in-place.
+ *
+ * Append a new STRTAB that has the new section names, followed by a new array
+ * ElfXX_Shdr[] that has the new section headers, followed by the section
+ * contents for __mcount_loc and its relocations.  The old shstrtab strings,
+ * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
+ * kilobytes.)  Subsequent processing by /bin/ld (or the kernel module loader)
+ * will ignore the garbage regions, because they are not designated by the
+ * new .e_shoff nor the new ElfXX_Shdr[].  [In order to remove the garbage,
+ * then use "ld -r" to create a new file that omits the garbage.]
+ */
+
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <elf.h>
+#include <fcntl.h>
+#include <setjmp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static int fd_map;	/* File descriptor for file being modified. */
+static int mmap_failed; /* Boolean flag. */
+static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
+static char gpfx;	/* prefix for global symbol name (sometimes '_') */
+static struct stat sb;	/* Remember .st_size, etc. */
+static jmp_buf jmpenv;	/* setjmp/longjmp per-file error escape */
+
+/* setjmp() return values */
+enum {
+	SJ_SETJMP = 0,  /* hardwired first return */
+	SJ_FAIL,
+	SJ_SUCCEED
+};
+
+/* Per-file resource cleanup when multiple files. */
+static void
+cleanup(void)
+{
+	if (!mmap_failed)
+		munmap(ehdr_curr, sb.st_size);
+	else
+		free(ehdr_curr);
+	close(fd_map);
+}
+
+static void __attribute__((noreturn))
+fail_file(void)
+{
+	cleanup();
+	longjmp(jmpenv, SJ_FAIL);
+}
+
+static void __attribute__((noreturn))
+succeed_file(void)
+{
+	cleanup();
+	longjmp(jmpenv, SJ_SUCCEED);
+}
+
+/* ulseek, uread, ...:  Check return value for errors. */
+
+static off_t
+ulseek(int const fd, off_t const offset, int const whence)
+{
+	off_t const w = lseek(fd, offset, whence);
+	if ((off_t)-1 == w) {
+		perror("lseek");
+		fail_file();
+	}
+	return w;
+}
+
+static size_t
+uread(int const fd, void *const buf, size_t const count)
+{
+	size_t const n = read(fd, buf, count);
+	if (n != count) {
+		perror("read");
+		fail_file();
+	}
+	return n;
+}
+
+static size_t
+uwrite(int const fd, void const *const buf, size_t const count)
+{
+	size_t const n = write(fd, buf, count);
+	if (n != count) {
+		perror("write");
+		fail_file();
+	}
+	return n;
+}
+
+static void *
+umalloc(size_t size)
+{
+	void *const addr = malloc(size);
+	if (0 == addr) {
+		fprintf(stderr, "malloc failed: %zu bytes\n", size);
+		fail_file();
+	}
+	return addr;
+}
+
+/*
+ * Get the whole file as a programming convenience in order to avoid
+ * malloc+lseek+read+free of many pieces.  If successful, then mmap
+ * avoids copying unused pieces; else just read the whole file.
+ * Open for both read and write; new info will be appended to the file.
+ * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
+ * do not propagate to the file until an explicit overwrite at the last.
+ * This preserves most aspects of consistency (all except .st_size)
+ * for simultaneous readers of the file while we are appending to it.
+ * However, multiple writers still are bad.  We choose not to use
+ * locking because it is expensive and the use case of kernel build
+ * makes multiple writers unlikely.
+ */
+static void *mmap_file(char const *fname)
+{
+	void *addr;
+
+	fd_map = open(fname, O_RDWR);
+	if (0 > fd_map || 0 > fstat(fd_map, &sb)) {
+		perror(fname);
+		fail_file();
+	}
+	if (!S_ISREG(sb.st_mode)) {
+		fprintf(stderr, "not a regular file: %s\n", fname);
+		fail_file();
+	}
+	addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
+		    fd_map, 0);
+	mmap_failed = 0;
+	if (MAP_FAILED == addr) {
+		mmap_failed = 1;
+		addr = umalloc(sb.st_size);
+		uread(fd_map, addr, sb.st_size);
+	}
+	return addr;
+}
+
+/* w8rev, w8nat, ...: Handle endianness. */
+
+static uint64_t w8rev(uint64_t const x)
+{
+	return   ((0xff & (x >> (0 * 8))) << (7 * 8))
+	       | ((0xff & (x >> (1 * 8))) << (6 * 8))
+	       | ((0xff & (x >> (2 * 8))) << (5 * 8))
+	       | ((0xff & (x >> (3 * 8))) << (4 * 8))
+	       | ((0xff & (x >> (4 * 8))) << (3 * 8))
+	       | ((0xff & (x >> (5 * 8))) << (2 * 8))
+	       | ((0xff & (x >> (6 * 8))) << (1 * 8))
+	       | ((0xff & (x >> (7 * 8))) << (0 * 8));
+}
+
+static uint32_t w4rev(uint32_t const x)
+{
+	return   ((0xff & (x >> (0 * 8))) << (3 * 8))
+	       | ((0xff & (x >> (1 * 8))) << (2 * 8))
+	       | ((0xff & (x >> (2 * 8))) << (1 * 8))
+	       | ((0xff & (x >> (3 * 8))) << (0 * 8));
+}
+
+static uint32_t w2rev(uint16_t const x)
+{
+	return   ((0xff & (x >> (0 * 8))) << (1 * 8))
+	       | ((0xff & (x >> (1 * 8))) << (0 * 8));
+}
+
+static uint64_t w8nat(uint64_t const x)
+{
+	return x;
+}
+
+static uint32_t w4nat(uint32_t const x)
+{
+	return x;
+}
+
+static uint32_t w2nat(uint16_t const x)
+{
+	return x;
+}
+
+static uint64_t (*w8)(uint64_t);
+static uint32_t (*w)(uint32_t);
+static uint32_t (*w2)(uint16_t);
+
+/* Names of the sections that could contain calls to mcount. */
+static int
+is_mcounted_section_name(char const *const txtname)
+{
+	return 0 == strcmp(".text",          txtname) ||
+		0 == strcmp(".sched.text",    txtname) ||
+		0 == strcmp(".spinlock.text", txtname) ||
+		0 == strcmp(".irqentry.text", txtname) ||
+		0 == strcmp(".text.unlikely", txtname);
+}
+
+/* Append the new shstrtab, Elf32_Shdr[], __mcount_loc and its relocations. */
+static void append32(Elf32_Ehdr *const ehdr,
+		     Elf32_Shdr *const shstr,
+		     uint32_t const *const mloc0,
+		     uint32_t const *const mlocp,
+		     Elf32_Rel const *const mrel0,
+		     Elf32_Rel const *const mrelp,
+		     unsigned int const rel_entsize,
+		     unsigned int const symsec_sh_link)
+{
+	/* Begin constructing output file */
+	Elf32_Shdr mcsec;
+	char const *mc_name = (sizeof(Elf32_Rela) == rel_entsize)
+		? ".rela__mcount_loc"
+		:  ".rel__mcount_loc";
+	unsigned const old_shnum = w2(ehdr->e_shnum);
+	uint32_t const old_shoff = w(ehdr->e_shoff);
+	uint32_t const old_shstr_sh_size   = w(shstr->sh_size);
+	uint32_t const old_shstr_sh_offset = w(shstr->sh_offset);
+	uint32_t t = 1 + strlen(mc_name) + w(shstr->sh_size);
+	uint32_t new_e_shoff;
+
+	shstr->sh_size = w(t);
+	shstr->sh_offset = w(sb.st_size);
+	t += sb.st_size;
+	t += (3u & -t);  /* 4-byte align */
+	new_e_shoff = t;
+
+	/* body for new shstrtab */
+	ulseek(fd_map, sb.st_size, SEEK_SET);
+	uwrite(fd_map, old_shstr_sh_offset + (void *)ehdr, old_shstr_sh_size);
+	uwrite(fd_map, mc_name, 1 + strlen(mc_name));
+
+	/* old(modified) Elf32_Shdr table, 4-byte aligned */
+	ulseek(fd_map, t, SEEK_SET);
+	t += sizeof(Elf32_Shdr) * old_shnum;
+	uwrite(fd_map, old_shoff + (void *)ehdr,
+	       sizeof(Elf32_Shdr) * old_shnum);
+
+	/* new sections __mcount_loc and .rel__mcount_loc */
+	t += 2*sizeof(mcsec);
+	mcsec.sh_name = w((sizeof(Elf32_Rela) == rel_entsize) + strlen(".rel")
+		+ old_shstr_sh_size);
+	mcsec.sh_type = w(SHT_PROGBITS);
+	mcsec.sh_flags = w(SHF_ALLOC);
+	mcsec.sh_addr = 0;
+	mcsec.sh_offset = w(t);
+	mcsec.sh_size = w((void *)mlocp - (void *)mloc0);
+	mcsec.sh_link = 0;
+	mcsec.sh_info = 0;
+	mcsec.sh_addralign = w(4);
+	mcsec.sh_entsize = w(4);
+	uwrite(fd_map, &mcsec, sizeof(mcsec));
+
+	mcsec.sh_name = w(old_shstr_sh_size);
+	mcsec.sh_type = (sizeof(Elf32_Rela) == rel_entsize)
+		? w(SHT_RELA)
+		: w(SHT_REL);
+	mcsec.sh_flags = 0;
+	mcsec.sh_addr = 0;
+	mcsec.sh_offset = w((void *)mlocp - (void *)mloc0 + t);
+	mcsec.sh_size   = w((void *)mrelp - (void *)mrel0);
+	mcsec.sh_link = w(symsec_sh_link);
+	mcsec.sh_info = w(old_shnum);
+	mcsec.sh_addralign = w(4);
+	mcsec.sh_entsize = w(rel_entsize);
+	uwrite(fd_map, &mcsec, sizeof(mcsec));
+
+	uwrite(fd_map, mloc0, (void *)mlocp - (void *)mloc0);
+	uwrite(fd_map, mrel0, (void *)mrelp - (void *)mrel0);
+
+	ehdr->e_shoff = w(new_e_shoff);
+	ehdr->e_shnum = w2(2 + w2(ehdr->e_shnum));  /* {.rel,}__mcount_loc */
+	ulseek(fd_map, 0, SEEK_SET);
+	uwrite(fd_map, ehdr, sizeof(*ehdr));
+}
+
+/*
+ * append64 and append32 (and other analogous pairs) could be templated
+ * using C++, but the complexity is high.  (For an example, look at p_elf.h
+ * in the source for UPX, http://upx.sourceforge.net)  So: remember to make
+ * the corresponding change in the routine for the other size.
+ */
+static void append64(Elf64_Ehdr *const ehdr,
+		     Elf64_Shdr *const shstr,
+		     uint64_t const *const mloc0,
+		     uint64_t const *const mlocp,
+		     Elf64_Rel const *const mrel0,
+		     Elf64_Rel const *const mrelp,
+		     unsigned int const rel_entsize,
+		     unsigned int const symsec_sh_link)
+{
+	/* Begin constructing output file */
+	Elf64_Shdr mcsec;
+	char const *mc_name = (sizeof(Elf64_Rela) == rel_entsize)
+		? ".rela__mcount_loc"
+		:  ".rel__mcount_loc";
+	unsigned const old_shnum = w2(ehdr->e_shnum);
+	uint64_t const old_shoff = w8(ehdr->e_shoff);
+	uint64_t const old_shstr_sh_size   = w8(shstr->sh_size);
+	uint64_t const old_shstr_sh_offset = w8(shstr->sh_offset);
+	uint64_t t = 1 + strlen(mc_name) + w8(shstr->sh_size);
+	uint64_t new_e_shoff;
+
+	shstr->sh_size = w8(t);
+	shstr->sh_offset = w8(sb.st_size);
+	t += sb.st_size;
+	t += (7u & -t);  /* 8-byte align */
+	new_e_shoff = t;
+
+	/* body for new shstrtab */
+	ulseek(fd_map, sb.st_size, SEEK_SET);
+	uwrite(fd_map, old_shstr_sh_offset + (void *)ehdr, old_shstr_sh_size);
+	uwrite(fd_map, mc_name, 1 + strlen(mc_name));
+
+	/* old(modified) Elf64_Shdr table, 8-byte aligned */
+	ulseek(fd_map, t, SEEK_SET);
+	t += sizeof(Elf64_Shdr) * old_shnum;
+	uwrite(fd_map, old_shoff + (void *)ehdr,
+		sizeof(Elf64_Shdr) * old_shnum);
+
+	/* new sections __mcount_loc and .rel__mcount_loc */
+	t += 2*sizeof(mcsec);
+	mcsec.sh_name = w((sizeof(Elf64_Rela) == rel_entsize) + strlen(".rel")
+		+ old_shstr_sh_size);
+	mcsec.sh_type = w(SHT_PROGBITS);
+	mcsec.sh_flags = w8(SHF_ALLOC);
+	mcsec.sh_addr = 0;
+	mcsec.sh_offset = w8(t);
+	mcsec.sh_size = w8((void *)mlocp - (void *)mloc0);
+	mcsec.sh_link = 0;
+	mcsec.sh_info = 0;
+	mcsec.sh_addralign = w8(8);
+	mcsec.sh_entsize = w8(8);
+	uwrite(fd_map, &mcsec, sizeof(mcsec));
+
+	mcsec.sh_name = w(old_shstr_sh_size);
+	mcsec.sh_type = (sizeof(Elf64_Rela) == rel_entsize)
+		? w(SHT_RELA)
+		: w(SHT_REL);
+	mcsec.sh_flags = 0;
+	mcsec.sh_addr = 0;
+	mcsec.sh_offset = w8((void *)mlocp - (void *)mloc0 + t);
+	mcsec.sh_size   = w8((void *)mrelp - (void *)mrel0);
+	mcsec.sh_link = w(symsec_sh_link);
+	mcsec.sh_info = w(old_shnum);
+	mcsec.sh_addralign = w8(8);
+	mcsec.sh_entsize = w8(rel_entsize);
+	uwrite(fd_map, &mcsec, sizeof(mcsec));
+
+	uwrite(fd_map, mloc0, (void *)mlocp - (void *)mloc0);
+	uwrite(fd_map, mrel0, (void *)mrelp - (void *)mrel0);
+
+	ehdr->e_shoff = w8(new_e_shoff);
+	ehdr->e_shnum = w2(2 + w2(ehdr->e_shnum));  /* {.rel,}__mcount_loc */
+	ulseek(fd_map, 0, SEEK_SET);
+	uwrite(fd_map, ehdr, sizeof(*ehdr));
+}
+
+/*
+ * 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 uint32_t *sift32_rel_mcount(uint32_t *mlocp,
+				   unsigned const offbase,
+				   Elf32_Rel **const mrelpp,
+				   Elf32_Shdr const *const relhdr,
+				   Elf32_Ehdr const *const ehdr,
+				   unsigned const recsym,
+				   uint32_t const recval,
+				   unsigned const reltype)
+{
+	uint32_t *const mloc0 = mlocp;
+	Elf32_Rel *mrelp = *mrelpp;
+	Elf32_Shdr *const shdr0 = (Elf32_Shdr *)(w(ehdr->e_shoff)
+		+ (void *)ehdr);
+	unsigned const symsec_sh_link = w(relhdr->sh_link);
+	Elf32_Shdr const *const symsec = &shdr0[symsec_sh_link];
+	Elf32_Sym const *const sym0 = (Elf32_Sym const *)(w(symsec->sh_offset)
+		+ (void *)ehdr);
+
+	Elf32_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
+	char const *const str0 = (char const *)(w(strsec->sh_offset)
+		+ (void *)ehdr);
+
+	Elf32_Rel const *const rel0 = (Elf32_Rel const *)(w(relhdr->sh_offset)
+		+ (void *)ehdr);
+	unsigned rel_entsize = w(relhdr->sh_entsize);
+	unsigned const nrel = w(relhdr->sh_size) / rel_entsize;
+	Elf32_Rel const *relp = rel0;
+
+	unsigned mcountsym = 0;
+	unsigned t;
+
+	for (t = nrel; t; --t) {
+		if (!mcountsym) {
+			Elf32_Sym const *const symp =
+				&sym0[ELF32_R_SYM(w(relp->r_info))];
+
+			if (0 == strcmp((('_' == gpfx) ? "_mcount" : "mcount"),
+					&str0[w(symp->st_name)]))
+				mcountsym = ELF32_R_SYM(w(relp->r_info));
+		}
+		if (mcountsym == ELF32_R_SYM(w(relp->r_info))) {
+			uint32_t const addend = w(w(relp->r_offset) - recval);
+			mrelp->r_offset = w(offbase
+				+ ((void *)mlocp - (void *)mloc0));
+			mrelp->r_info = w(ELF32_R_INFO(recsym, reltype));
+			if (sizeof(Elf32_Rela) == rel_entsize) {
+				((Elf32_Rela *)mrelp)->r_addend = addend;
+				*mlocp++ = 0;
+			} else
+				*mlocp++ = addend;
+
+			mrelp = (Elf32_Rel *)(rel_entsize + (void *)mrelp);
+		}
+		relp = (Elf32_Rel const *)(rel_entsize + (void *)relp);
+	}
+	*mrelpp = mrelp;
+	return mlocp;
+}
+
+static uint64_t *sift64_rel_mcount(uint64_t *mlocp,
+				   unsigned const offbase,
+				   Elf64_Rel **const mrelpp,
+				   Elf64_Shdr const *const relhdr,
+				   Elf64_Ehdr const *const ehdr,
+				   unsigned const recsym,
+				   uint64_t const recval,
+				   unsigned const reltype)
+{
+	uint64_t *const mloc0 = mlocp;
+	Elf64_Rel *mrelp = *mrelpp;
+	Elf64_Shdr *const shdr0 = (Elf64_Shdr *)(w8(ehdr->e_shoff)
+		+ (void *)ehdr);
+	unsigned const symsec_sh_link = w(relhdr->sh_link);
+	Elf64_Shdr const *const symsec = &shdr0[symsec_sh_link];
+	Elf64_Sym const *const sym0 = (Elf64_Sym const *)(w8(symsec->sh_offset)
+		+ (void *)ehdr);
+
+	Elf64_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
+	char const *const str0 = (char const *)(w8(strsec->sh_offset)
+		+ (void *)ehdr);
+
+	Elf64_Rel const *const rel0 = (Elf64_Rel const *)(w8(relhdr->sh_offset)
+		+ (void *)ehdr);
+	unsigned rel_entsize = w8(relhdr->sh_entsize);
+	unsigned const nrel = w8(relhdr->sh_size) / rel_entsize;
+	Elf64_Rel const *relp = rel0;
+
+	unsigned mcountsym = 0;
+	unsigned t;
+
+	for (t = nrel; 0 != t; --t) {
+		if (!mcountsym) {
+			Elf64_Sym const *const symp =
+				&sym0[ELF64_R_SYM(w8(relp->r_info))];
+			char const *symname = &str0[w(symp->st_name)];
+
+			if ('.' == symname[0])
+				++symname;  /* ppc64 hack */
+			if (0 == strcmp((('_' == gpfx) ? "_mcount" : "mcount"),
+					symname))
+				mcountsym = ELF64_R_SYM(w8(relp->r_info));
+		}
+
+		if (mcountsym == ELF64_R_SYM(w8(relp->r_info))) {
+			uint64_t const addend = w8(w8(relp->r_offset) - recval);
+
+			mrelp->r_offset = w8(offbase
+				+ ((void *)mlocp - (void *)mloc0));
+			mrelp->r_info = w8(ELF64_R_INFO(recsym, reltype));
+			if (sizeof(Elf64_Rela) == rel_entsize) {
+				((Elf64_Rela *)mrelp)->r_addend = addend;
+				*mlocp++ = 0;
+			} else
+				*mlocp++ = addend;
+
+			mrelp = (Elf64_Rel *)(rel_entsize + (void *)mrelp);
+		}
+		relp = (Elf64_Rel const *)(rel_entsize + (void *)relp);
+	}
+	*mrelpp = mrelp;
+
+	return mlocp;
+}
+
+/*
+ * Find a symbol in the given section, to be used as the base for relocating
+ * the table of offsets of calls to mcount.  A local or global symbol suffices,
+ * but avoid a Weak symbol because it may be overridden; the change in value
+ * would invalidate the relocations of the offsets of the calls to mcount.
+ * Often the found symbol will be the unnamed local symbol generated by
+ * GNU 'as' for the start of each section.  For example:
+ *    Num:    Value  Size Type    Bind   Vis      Ndx Name
+ *      2: 00000000     0 SECTION LOCAL  DEFAULT    1
+ */
+static unsigned find32_secsym_ndx(unsigned const txtndx,
+				  char const *const txtname,
+				  uint32_t *const recvalp,
+				  Elf32_Shdr const *const symhdr,
+				  Elf32_Ehdr const *const ehdr)
+{
+	Elf32_Sym const *const sym0 = (Elf32_Sym const *)(w(symhdr->sh_offset)
+		+ (void *)ehdr);
+	unsigned const nsym = w(symhdr->sh_size) / w(symhdr->sh_entsize);
+	Elf32_Sym const *symp;
+	unsigned t;
+
+	for (symp = sym0, t = nsym; t; --t, ++symp) {
+		unsigned int const st_bind = ELF32_ST_BIND(symp->st_info);
+
+		if (txtndx == w2(symp->st_shndx)
+			/* avoid STB_WEAK */
+		    && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
+			*recvalp = w(symp->st_value);
+			return symp - sym0;
+		}
+	}
+	fprintf(stderr, "Cannot find symbol for section %d: %s.\n",
+		txtndx, txtname);
+	fail_file();
+}
+
+static unsigned find64_secsym_ndx(unsigned const txtndx,
+				  char const *const txtname,
+				  uint64_t *const recvalp,
+				  Elf64_Shdr const *const symhdr,
+				  Elf64_Ehdr const *const ehdr)
+{
+	Elf64_Sym const *const sym0 = (Elf64_Sym const *)(w8(symhdr->sh_offset)
+		+ (void *)ehdr);
+	unsigned const nsym = w8(symhdr->sh_size) / w8(symhdr->sh_entsize);
+	Elf64_Sym const *symp;
+	unsigned t;
+
+	for (symp = sym0, t = nsym; t; --t, ++symp) {
+		unsigned int const st_bind = ELF64_ST_BIND(symp->st_info);
+
+		if (txtndx == w2(symp->st_shndx)
+			/* avoid STB_WEAK */
+		    && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
+			*recvalp = w8(symp->st_value);
+			return symp - sym0;
+		}
+	}
+	fprintf(stderr, "Cannot find symbol for section %d: %s.\n",
+		txtndx, txtname);
+	fail_file();
+}
+
+/*
+ * Evade ISO C restriction: no declaration after statement in
+ * has32_rel_mcount.
+ */
+static char const *
+__has32_rel_mcount(Elf32_Shdr const *const relhdr,  /* is SHT_REL or SHT_RELA */
+		   Elf32_Shdr const *const shdr0,
+		   char const *const shstrtab,
+		   char const *const fname)
+{
+	/* .sh_info depends on .sh_type == SHT_REL[,A] */
+	Elf32_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
+	char const *const txtname = &shstrtab[w(txthdr->sh_name)];
+
+	if (0 == strcmp("__mcount_loc", txtname)) {
+		fprintf(stderr, "warning: __mcount_loc already exists: %s\n",
+			fname);
+		succeed_file();
+	}
+	if (SHT_PROGBITS != w(txthdr->sh_type) ||
+	    !is_mcounted_section_name(txtname))
+		return NULL;
+	return txtname;
+}
+
+static char const *has32_rel_mcount(Elf32_Shdr const *const relhdr,
+				    Elf32_Shdr const *const shdr0,
+				    char const *const shstrtab,
+				    char const *const fname)
+{
+	if (SHT_REL  != w(relhdr->sh_type) && SHT_RELA != w(relhdr->sh_type))
+		return NULL;
+	return __has32_rel_mcount(relhdr, shdr0, shstrtab, fname);
+}
+
+static char const *__has64_rel_mcount(Elf64_Shdr const *const relhdr,
+				      Elf64_Shdr const *const shdr0,
+				      char const *const shstrtab,
+				      char const *const fname)
+{
+	/* .sh_info depends on .sh_type == SHT_REL[,A] */
+	Elf64_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
+	char const *const txtname = &shstrtab[w(txthdr->sh_name)];
+
+	if (0 == strcmp("__mcount_loc", txtname)) {
+		fprintf(stderr, "warning: __mcount_loc already exists: %s\n",
+			fname);
+		succeed_file();
+	}
+	if (SHT_PROGBITS != w(txthdr->sh_type) ||
+	    !is_mcounted_section_name(txtname))
+		return NULL;
+	return txtname;
+}
+
+static char const *has64_rel_mcount(Elf64_Shdr const *const relhdr,
+				    Elf64_Shdr const *const shdr0,
+				    char const *const shstrtab,
+				    char const *const fname)
+{
+	if (SHT_REL  != w(relhdr->sh_type) && SHT_RELA != w(relhdr->sh_type))
+		return NULL;
+	return __has64_rel_mcount(relhdr, shdr0, shstrtab, fname);
+}
+
+static unsigned tot32_relsize(Elf32_Shdr const *const shdr0,
+			      unsigned nhdr,
+			      const char *const shstrtab,
+			      const char *const fname)
+{
+	unsigned totrelsz = 0;
+	Elf32_Shdr const *shdrp = shdr0;
+	for (; 0 != nhdr; --nhdr, ++shdrp) {
+		if (has32_rel_mcount(shdrp, shdr0, shstrtab, fname))
+			totrelsz += w(shdrp->sh_size);
+	}
+	return totrelsz;
+}
+
+static unsigned tot64_relsize(Elf64_Shdr const *const shdr0,
+			      unsigned nhdr,
+			      const char *const shstrtab,
+			      const char *const fname)
+{
+	unsigned totrelsz = 0;
+	Elf64_Shdr const *shdrp = shdr0;
+
+	for (; nhdr; --nhdr, ++shdrp) {
+		if (has64_rel_mcount(shdrp, shdr0, shstrtab, fname))
+			totrelsz += w8(shdrp->sh_size);
+	}
+	return totrelsz;
+}
+
+/* Overall supervision for Elf32 ET_REL file. */
+static void
+do32(Elf32_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
+{
+	Elf32_Shdr *const shdr0 = (Elf32_Shdr *)(w(ehdr->e_shoff)
+		+ (void *)ehdr);
+	unsigned const nhdr = w2(ehdr->e_shnum);
+	Elf32_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
+	char const *const shstrtab = (char const *)(w(shstr->sh_offset)
+		+ (void *)ehdr);
+
+	Elf32_Shdr const *relhdr;
+	unsigned k;
+
+	/* Upper bound on space: assume all relevant relocs are for mcount. */
+	unsigned const totrelsz = tot32_relsize(shdr0, nhdr, shstrtab, fname);
+	Elf32_Rel *const mrel0 = umalloc(totrelsz);
+	Elf32_Rel *      mrelp = mrel0;
+
+	/* 2*sizeof(address) <= sizeof(Elf32_Rel) */
+	uint32_t *const mloc0 = umalloc(totrelsz>>1);
+	uint32_t *      mlocp = mloc0;
+
+	unsigned rel_entsize = 0;
+	unsigned symsec_sh_link = 0;
+
+	for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
+		char const *const txtname = has32_rel_mcount(relhdr, shdr0,
+			shstrtab, fname);
+		if (txtname) {
+			uint32_t recval = 0;
+			unsigned const recsym = find32_secsym_ndx(
+				w(relhdr->sh_info), txtname, &recval,
+				&shdr0[symsec_sh_link = w(relhdr->sh_link)],
+				ehdr);
+
+			rel_entsize = w(relhdr->sh_entsize);
+			mlocp = sift32_rel_mcount(mlocp,
+				(void *)mlocp - (void *)mloc0, &mrelp,
+				relhdr, ehdr, recsym, recval, reltype);
+		}
+	}
+	if (mloc0 != mlocp) {
+		append32(ehdr, shstr, mloc0, mlocp, mrel0, mrelp,
+			rel_entsize, symsec_sh_link);
+	}
+	free(mrel0);
+	free(mloc0);
+}
+
+static void
+do64(Elf64_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
+{
+	Elf64_Shdr *const shdr0 = (Elf64_Shdr *)(w8(ehdr->e_shoff)
+		+ (void *)ehdr);
+	unsigned const nhdr = w2(ehdr->e_shnum);
+	Elf64_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
+	char const *const shstrtab = (char const *)(w8(shstr->sh_offset)
+		+ (void *)ehdr);
+
+	Elf64_Shdr const *relhdr;
+	unsigned k;
+
+	/* Upper bound on space: assume all relevant relocs are for mcount. */
+	unsigned const totrelsz = tot64_relsize(shdr0, nhdr, shstrtab, fname);
+	Elf64_Rel *const mrel0 = umalloc(totrelsz);
+	Elf64_Rel *      mrelp = mrel0;
+
+	/* 2*sizeof(address) <= sizeof(Elf64_Rel) */
+	uint64_t *const mloc0 = umalloc(totrelsz>>1);
+	uint64_t *      mlocp = mloc0;
+
+	unsigned rel_entsize = 0;
+	unsigned symsec_sh_link = 0;
+
+	for ((relhdr = shdr0), k = nhdr; k; --k, ++relhdr) {
+		char const *const txtname = has64_rel_mcount(relhdr, shdr0,
+			shstrtab, fname);
+		if (txtname) {
+			uint64_t recval = 0;
+			unsigned const recsym = find64_secsym_ndx(
+				w(relhdr->sh_info), txtname, &recval,
+				&shdr0[symsec_sh_link = w(relhdr->sh_link)],
+				ehdr);
+
+			rel_entsize = w8(relhdr->sh_entsize);
+			mlocp = sift64_rel_mcount(mlocp,
+				(void *)mlocp - (void *)mloc0, &mrelp,
+				relhdr, ehdr, recsym, recval, reltype);
+		}
+	}
+	if (mloc0 != mlocp) {
+		append64(ehdr, shstr, mloc0, mlocp, mrel0, mrelp,
+			rel_entsize, symsec_sh_link);
+	}
+	free(mrel0);
+	free(mloc0);
+}
+
+static void
+do_file(char const *const fname)
+{
+	Elf32_Ehdr *const ehdr = mmap_file(fname);
+	unsigned int reltype = 0;
+
+	ehdr_curr = ehdr;
+	w = w4nat;
+	w2 = w2nat;
+	w8 = w8nat;
+	switch (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);
+		fail_file();
+	} break;
+	case ELFDATA2LSB: {
+		if (1 != *(unsigned char const *)&endian) {
+			/* main() is big endian, file.o is little endian. */
+			w = w4rev;
+			w2 = w2rev;
+			w8 = w8rev;
+		}
+	} break;
+	case ELFDATA2MSB: {
+		if (0 != *(unsigned char const *)&endian) {
+			/* main() is little endian, file.o is big endian. */
+			w = w4rev;
+			w2 = w2rev;
+			w8 = w8rev;
+		}
+	} break;
+	}  /* end switch */
+	if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
+	||  ET_REL != w2(ehdr->e_type)
+	||  EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
+		fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
+		fail_file();
+	}
+
+	gpfx = 0;
+	switch (w2(ehdr->e_machine)) {
+	default: {
+		fprintf(stderr, "unrecognized e_machine %d %s\n",
+			w2(ehdr->e_machine), fname);
+		fail_file();
+	} break;
+	case EM_386:	 reltype = R_386_32;                   break;
+	case EM_ARM:	 reltype = R_ARM_ABS32;                break;
+	case EM_IA_64:	 reltype = R_IA64_IMM64;   gpfx = '_'; break;
+	case EM_PPC:	 reltype = R_PPC_ADDR32;   gpfx = '_'; break;
+	case EM_PPC64:	 reltype = R_PPC64_ADDR64; gpfx = '_'; break;
+	case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
+	case EM_SH:	 reltype = R_SH_DIR32;                 break;
+	case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
+	case EM_X86_64:	 reltype = R_X86_64_64;                break;
+	}  /* end switch */
+
+	switch (ehdr->e_ident[EI_CLASS]) {
+	default: {
+		fprintf(stderr, "unrecognized ELF class %d %s\n",
+			ehdr->e_ident[EI_CLASS], fname);
+		fail_file();
+	} break;
+	case ELFCLASS32: {
+		if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
+		||  sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
+			fprintf(stderr,
+				"unrecognized ET_REL file: %s\n", fname);
+			fail_file();
+		}
+		if (EM_S390 == w2(ehdr->e_machine))
+			reltype = R_390_32;
+		do32(ehdr, fname, reltype);
+	} break;
+	case ELFCLASS64: {
+		Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
+		if (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
+		||  sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
+			fprintf(stderr,
+				"unrecognized ET_REL file: %s\n", fname);
+			fail_file();
+		}
+		if (EM_S390 == w2(ghdr->e_machine))
+			reltype = R_390_64;
+		do64(ghdr, fname, reltype);
+	} break;
+	}  /* end switch */
+
+	cleanup();
+}
+
+int
+main(int argc, char const *argv[])
+{
+	int n_error = 0;  /* gcc-4.3.0 false positive complaint */
+	if (argc <= 1)
+		fprintf(stderr, "usage: recordmcount file.o...\n");
+	else  /* Process each file in turn, allowing deep failure. */
+	for (--argc, ++argv; 0 < argc; --argc, ++argv) {
+		int const sjval = setjmp(jmpenv);
+		switch (sjval) {
+		default: {
+			fprintf(stderr, "internal error: %s\n", argv[0]);
+			exit(1);
+		} break;
+		case SJ_SETJMP: {  /* normal sequence */
+			/* Avoid problems if early cleanup() */
+			fd_map = -1;
+			ehdr_curr = NULL;
+			mmap_failed = 1;
+			do_file(argv[0]);
+		} break;
+		case SJ_FAIL: {  /* error in do_file or below */
+			++n_error;
+		} break;
+		case SJ_SUCCEED: {  /* premature success */
+			/* do nothing */
+		} break;
+		}  /* end switch */
+	}
+	return !!n_error;
+}
+
+