[PATCH 1/2] jump labels: Add infrastructure to update jump labels at compiletime

[Steven Rostedt]

From: Steven Rostedt <srostedt@xxxxxxxxxx>

Add the infrastructure to allow architectures to modify the jump label
locations at compile time. This is mainly for x86, where the jmps may
be either 2 bytes or 5 bytes. Instead of wasting 5 bytes for all jump labels,
this code will let x86 put in a jmp instead of a 5 byte nop. Then the
assembler will make either a 2 byte or 5 byte jmp depending on where
the target is.

At compile time, this code will replace the jmps with either a 2 byte
or 5 byte nop depending on the size of the jmp that was added.

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 Makefile                    |    7 +
 arch/Kconfig                |    6 +
 scripts/Makefile            |    1 +
 scripts/Makefile.build      |   15 ++-
 scripts/update_jump_label.c |  335 +++++++++++++++++++++++++++++++++++++++++++
 scripts/update_jump_label.h |  283 ++++++++++++++++++++++++++++++++++++
 6 files changed, 645 insertions(+), 2 deletions(-)
 create mode 100644 scripts/update_jump_label.c
 create mode 100644 scripts/update_jump_label.h

diff --git a/Makefile b/Makefile
index adddd11..2b3fdf3 100644
--- a/Makefile
+++ b/Makefile
@@ -611,6 +611,13 @@ ifdef CONFIG_DYNAMIC_FTRACE
 endif
 endif
 
+ifdef CONFIG_JUMP_LABEL
+	ifdef CONFIG_HAVE_BUILD_TIME_JUMP_LABEL
+		BUILD_UPDATE_JUMP_LABEL := y
+		export BUILD_UPDATE_JUMP_LABEL
+	endif
+endif
+
 # We trigger additional mismatches with less inlining
 ifdef CONFIG_DEBUG_SECTION_MISMATCH
 KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
diff --git a/arch/Kconfig b/arch/Kconfig
index 4b0669c..8fa6934 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -169,6 +169,12 @@ config HAVE_PERF_EVENTS_NMI
 	  subsystem.  Also has support for calculating CPU cycle events
 	  to determine how many clock cycles in a given period.
 
+config HAVE_BUILD_TIME_JUMP_LABEL
+       bool
+       help
+	If an arch uses scripts/update_jump_label to patch in jump nops
+	at build time, then it must enable this option.
+
 config HAVE_ARCH_JUMP_LABEL
 	bool
 
diff --git a/scripts/Makefile b/scripts/Makefile
index df7678f..738b65c 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -13,6 +13,7 @@ hostprogs-$(CONFIG_LOGO)         += pnmtologo
 hostprogs-$(CONFIG_VT)           += conmakehash
 hostprogs-$(CONFIG_IKCONFIG)     += bin2c
 hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
+hostprogs-$(BUILD_UPDATE_JUMP_LABEL) += update_jump_label
 
 always		:= $(hostprogs-y) $(hostprogs-m)
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index d2b366c..8a84b80 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -258,6 +258,15 @@ cmd_modversions =								\
 	fi;
 endif
 
+ifdef BUILD_UPDATE_JUMP_LABEL
+update_jump_label_source := $(srctree)/scripts/update_jump_label.c \
+			$(srctree)/scripts/update_jump_label.h
+cmd_update_jump_label =						\
+	if [ $(@) != "scripts/mod/empty.o" ]; then		\
+		$(objtree)/scripts/update_jump_label "$(@)";	\
+	fi;
+endif
+
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
 ifdef BUILD_C_RECORDMCOUNT
 ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
@@ -294,6 +303,7 @@ define rule_cc_o_c
 	$(cmd_modversions)						  \
 	$(call echo-cmd,record_mcount)					  \
 	$(cmd_record_mcount)						  \
+	$(cmd_update_jump_label)					  \
 	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
 	                                              $(dot-target).tmp;  \
 	rm -f $(depfile);						  \
@@ -301,13 +311,14 @@ define rule_cc_o_c
 endef
 
 # Built-in and composite module parts
-$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
+$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(update_jump_label_source) FORCE
 	$(call cmd,force_checksrc)
 	$(call if_changed_rule,cc_o_c)
 
 # Single-part modules are special since we need to mark them in $(MODVERDIR)
 
-$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
+$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) \
+		  $(update_jump_label_source) FORCE
 	$(call cmd,force_checksrc)
 	$(call if_changed_rule,cc_o_c)
 	@{ echo $(@:.o=.ko); echo $@; } > $(MODVERDIR)/$(@F:.o=.mod)
diff --git a/scripts/update_jump_label.c b/scripts/update_jump_label.c
new file mode 100644
index 0000000..399d898
--- /dev/null
+++ b/scripts/update_jump_label.c
@@ -0,0 +1,335 @@
+/*
+ * update_jump_label.c: replace jmps with nops at compile time.
+ * Copyright 2010 Steven Rostedt <srostedt@xxxxxxxxxx>, Red Hat Inc.
+ *  Parsing of the elf file was influenced by recordmcount.c
+ *  originally written by and copyright to John F. Reiser <jreiser@xxxxxxxxxxxx>.
+ */
+
+/*
+ * Note, this code is originally designed for x86, but may be used by
+ * other archs to do the nop updates at compile time instead of at boot time.
+ * X86 uses this as an optimization, as jmps can be either 2 bytes or 5 bytes.
+ * Inserting a 2 byte where possible helps with both CPU performance and
+ * icache strain.
+ */
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <getopt.h>
+#include <elf.h>
+#include <fcntl.h>
+#include <setjmp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <unistd.h>
+
+static int fd_map;	/* File descriptor for file being modified. */
+static struct stat sb;	/* Remember .st_size, etc. */
+static int mmap_failed; /* Boolean flag. */
+
+static void die(const char *err, const char *fmt, ...)
+{
+	va_list ap;
+
+	if (err)
+		perror(err);
+
+	if (fmt) {
+		va_start(ap, fmt);
+		fprintf(stderr, "Fatal error:  ");
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, "\n");
+		va_end(ap);
+	}
+
+	exit(1);
+}
+
+static void usage(char **argv)
+{
+	char *arg = argv[0];
+	char *p = arg+strlen(arg);
+
+	while (p >= arg && *p != '/')
+		p--;
+	p++;
+
+	printf("usage: %s file\n"
+	       "\n", p);
+	exit(-1);
+}
+
+/* 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);
+
+/* 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 (w == (off_t)-1)
+		die("lseek", NULL);
+
+	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)
+		die("read", NULL);
+
+	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)
+		die("write", NULL);
+
+	return n;
+}
+
+static void *
+umalloc(size_t size)
+{
+	void *const addr = malloc(size);
+	if (addr == 0)
+		die("malloc", "malloc failed: %zu bytes\n", size);
+
+	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 (fd_map < 0 || fstat(fd_map, &sb) < 0)
+		die(fname, "failed to open file");
+
+	if (!S_ISREG(sb.st_mode))
+		die(NULL, "not a regular file: %s\n", fname);
+
+	addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
+		    fd_map, 0);
+
+	mmap_failed = 0;
+	if (addr == MAP_FAILED) {
+		mmap_failed = 1;
+		addr = umalloc(sb.st_size);
+		uread(fd_map, addr, sb.st_size);
+	}
+	return addr;
+}
+
+static void munmap_file(void *addr)
+{
+	if (!mmap_failed)
+		munmap(addr, sb.st_size);
+	else
+		free(addr);
+	close(fd_map);
+}
+
+static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
+static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
+static unsigned char ideal_nop2_x86[2] = { 0x66, 0x90 };
+static unsigned char *ideal_nop;
+
+static int (*make_nop)(void *map, size_t const offset);
+
+static int make_nop_x86(void *map, size_t const offset)
+{
+	unsigned char *op;
+	unsigned char *nop;
+	int size;
+
+	/* Determine which type of jmp this is 2 byte or 5. */
+	op = map + offset;
+	switch (*op) {
+	case 0xeb: /* 2 byte */
+		size = 2;
+		nop = ideal_nop2_x86;
+		break;
+	case 0xe9: /* 5 byte */
+		size = 5;
+		nop = ideal_nop;
+		break;
+	default:
+		die(NULL, "Bad jump label section (bad op %x)\n", *op);
+		__builtin_unreachable();
+	}
+
+	/* convert to nop */
+	ulseek(fd_map, offset, SEEK_SET);
+	uwrite(fd_map, nop, size);
+	return 0;
+}
+
+/* 32 bit and 64 bit are very similar */
+#include "update_jump_label.h"
+#define UPDATE_JUMP_LABEL_64
+#include "update_jump_label.h"
+
+static int do_file(const char *fname)
+{
+	Elf32_Ehdr *const ehdr = mmap_file(fname);
+	unsigned int reltype = 0;
+
+	w = w4nat;
+	w2 = w2nat;
+	w8 = w8nat;
+	switch (ehdr->e_ident[EI_DATA]) {
+		static unsigned int const endian = 1;
+	default:
+		die(NULL, "unrecognized ELF data encoding %d: %s\n",
+			ehdr->e_ident[EI_DATA], fname);
+		break;
+	case ELFDATA2LSB:
+		if (*(unsigned char const *)&endian != 1) {
+			/* main() is big endian, file.o is little endian. */
+			w = w4rev;
+			w2 = w2rev;
+			w8 = w8rev;
+		}
+		break;
+	case ELFDATA2MSB:
+		if (*(unsigned char const *)&endian != 0) {
+			/* main() is little endian, file.o is big endian. */
+			w = w4rev;
+			w2 = w2rev;
+			w8 = w8rev;
+		}
+		break;
+	}  /* end switch */
+
+	if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 ||
+	    w2(ehdr->e_type) != ET_REL ||
+	    ehdr->e_ident[EI_VERSION] != EV_CURRENT)
+		die(NULL, "unrecognized ET_REL file %s\n", fname);
+
+	switch (w2(ehdr->e_machine)) {
+	default:
+		die(NULL, "unrecognized e_machine %d %s\n",
+		    w2(ehdr->e_machine), fname);
+		break;
+	case EM_386:
+		reltype = R_386_32;
+		make_nop = make_nop_x86;
+		ideal_nop = ideal_nop5_x86_32;
+		break;
+	case EM_ARM:	 reltype = R_ARM_ABS32;
+			 break;
+	case EM_IA_64:	 reltype = R_IA64_IMM64; break;
+	case EM_MIPS:	 /* reltype: e_class    */ break;
+	case EM_PPC:	 reltype = R_PPC_ADDR32;   break;
+	case EM_PPC64:	 reltype = R_PPC64_ADDR64; break;
+	case EM_S390:    /* reltype: e_class    */ break;
+	case EM_SH:	 reltype = R_SH_DIR32;                 break;
+	case EM_SPARCV9: reltype = R_SPARC_64;     break;
+	case EM_X86_64:
+		make_nop = make_nop_x86;
+		ideal_nop = ideal_nop5_x86_64;
+		reltype = R_X86_64_64;
+		break;
+	}  /* end switch */
+
+	switch (ehdr->e_ident[EI_CLASS]) {
+	default:
+		die(NULL, "unrecognized ELF class %d %s\n",
+		    ehdr->e_ident[EI_CLASS], fname);
+		break;
+	case ELFCLASS32:
+		if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
+		||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr))
+			die(NULL, "unrecognized ET_REL file: %s\n", fname);
+
+		do_func32(ehdr, fname, 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))
+			die(NULL, "unrecognized ET_REL file: %s\n", fname);
+
+		do_func64(ghdr, fname, reltype);
+		break;
+	}
+	}  /* end switch */
+
+	munmap_file(ehdr);
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	if (argc != 2)
+		usage(argv);
+
+	return do_file(argv[1]);
+}
+
diff --git a/scripts/update_jump_label.h b/scripts/update_jump_label.h
new file mode 100644
index 0000000..8810557
--- /dev/null
+++ b/scripts/update_jump_label.h
@@ -0,0 +1,283 @@
+/*
+ * update_jump_label.h
+ *
+ * This code was taken out of recordmcount.c written by
+ * Copyright 2009 John F. Reiser <jreiser@xxxxxxxxxxxx>.  All rights reserved.
+ *
+ * The original code had the same algorithms for both 32bit
+ * and 64bit ELF files, but the code was duplicated to support
+ * the difference in structures that were used. This
+ * file creates a macro of everything that is different between
+ * the 64 and 32 bit code, such that by including this header
+ * twice we can create both sets of functions by including this
+ * header once with RECORD_MCOUNT_64 undefined, and again with
+ * it defined.
+ *
+ * This conversion to macros was done by:
+ * Copyright 2010 Steven Rostedt <srostedt@xxxxxxxxxx>, Red Hat Inc.
+ *
+ * Licensed under the GNU General Public License, version 2 (GPLv2).
+ */
+
+#undef EBITS
+#undef _w
+#undef _align
+#undef _size
+
+#ifdef UPDATE_JUMP_LABEL_64
+# define EBITS			64
+# define _w			w8
+# define _align			7u
+# define _size			8
+#else
+# define EBITS			32
+# define _w			w
+# define _align			3u
+# define _size			4
+#endif
+
+#define _FBITS(x, e)	x##e
+#define FBITS(x, e)	_FBITS(x, e)
+#define FUNC(x)		FBITS(x, EBITS)
+
+#undef Elf_Addr
+#undef Elf_Ehdr
+#undef Elf_Shdr
+#undef Elf_Rel
+#undef Elf_Rela
+#undef Elf_Sym
+#undef ELF_R_SYM
+#undef ELF_R_TYPE
+
+#define __ATTACH(x, y, z)	x##y##z
+#define ATTACH(x, y, z)		__ATTACH(x, y, z)
+
+#define Elf_Addr	ATTACH(Elf, EBITS, _Addr)
+#define Elf_Ehdr	ATTACH(Elf, EBITS, _Ehdr)
+#define Elf_Shdr	ATTACH(Elf, EBITS, _Shdr)
+#define Elf_Rel		ATTACH(Elf, EBITS, _Rel)
+#define Elf_Rela	ATTACH(Elf, EBITS, _Rela)
+#define Elf_Sym		ATTACH(Elf, EBITS, _Sym)
+#define uint_t		ATTACH(uint, EBITS, _t)
+#define ELF_R_SYM	ATTACH(ELF, EBITS, _R_SYM)
+#define ELF_R_TYPE	ATTACH(ELF, EBITS, _R_TYPE)
+
+#undef get_shdr
+#define get_shdr(ehdr) ((Elf_Shdr *)(_w((ehdr)->e_shoff) + (void *)(ehdr)))
+
+#undef get_section_loc
+#define get_section_loc(ehdr, shdr)(_w((shdr)->sh_offset) + (void *)(ehdr))
+
+/* Functions and pointers that do_file() may override for specific e_machine. */
+
+static void FUNC(get_sym_str_and_relp)(Elf_Shdr const *const relhdr,
+				 Elf_Ehdr const *const ehdr,
+				 Elf_Sym const **sym0,
+				 char const **str0,
+				 Elf_Rel const **relp)
+{
+	Elf_Shdr *const shdr0 = get_shdr(ehdr);
+	unsigned const symsec_sh_link = w(relhdr->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 *)get_section_loc(ehdr, relhdr);
+
+	*sym0 = (Elf_Sym const *)get_section_loc(ehdr, symsec);
+
+	*str0 = (char const *)get_section_loc(ehdr, strsec);
+
+	*relp = rel0;
+}
+
+/*
+ * Read the relocation table again, but this time its called on sections
+ * that are not going to be traced. The mcount calls here will be converted
+ * into nops.
+ */
+static void FUNC(nop_jump_label)(Elf_Shdr const *const relhdr,
+		       Elf_Ehdr const *const ehdr,
+		       const char *const txtname)
+{
+	Elf_Shdr *const shdr0 = get_shdr(ehdr);
+	Elf_Sym const *sym0;
+	char const *str0;
+	Elf_Rel const *relp;
+	Elf_Rela const *relap;
+	Elf_Shdr const *const shdr = &shdr0[w(relhdr->sh_info)];
+	unsigned rel_entsize = w(relhdr->sh_entsize);
+	unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
+	int t;
+
+	FUNC(get_sym_str_and_relp)(relhdr, ehdr, &sym0, &str0, &relp);
+
+	for (t = nrel; t > 0; t -= 3) {
+		int ret = -1;
+
+		relap = (Elf_Rela const *)relp;
+		printf("rel offset=%lx info=%lx sym=%lx type=%lx addend=%lx\n",
+		       (long)relap->r_offset, (long)relap->r_info,
+		       (long)ELF_R_SYM(relap->r_info),
+		       (long)ELF_R_TYPE(relap->r_info),
+		       (long)relap->r_addend);
+
+		if (0 && make_nop)
+			ret = make_nop((void *)ehdr, shdr->sh_offset + relp->r_offset);
+
+		/* jump label sections are paired in threes */
+		relp = (Elf_Rel const *)(rel_entsize * 3 + (void *)relp);
+	}
+}
+
+/* Find relocation section hdr for a given section */
+static const Elf_Shdr *
+FUNC(find_relhdr)(const Elf_Ehdr *ehdr, const Elf_Shdr *shdr)
+{
+	const Elf_Shdr *shdr0 = get_shdr(ehdr);
+	int nhdr = w2(ehdr->e_shnum);
+	const Elf_Shdr *hdr;
+	int i;
+
+	for (hdr = shdr0, i = 0; i < nhdr; hdr = &shdr0[++i]) {
+		if (w(hdr->sh_type) != SHT_REL &&
+		    w(hdr->sh_type) != SHT_RELA)
+			continue;
+
+		/*
+		 * The relocation section's info field holds
+		 * the section index that it represents.
+		 */
+		if (shdr == &shdr0[w(hdr->sh_info)])
+			return hdr;
+	}
+	return NULL;
+}
+
+/* Find a section headr based on name and type */
+static const Elf_Shdr *
+FUNC(find_shdr)(const Elf_Ehdr *ehdr, const char *name, uint_t type)
+{
+	const Elf_Shdr *shdr0 = get_shdr(ehdr);
+	const Elf_Shdr *shstr = &shdr0[w2(ehdr->e_shstrndx)];
+	const char *shstrtab = (char *)get_section_loc(ehdr, shstr);
+	int nhdr = w2(ehdr->e_shnum);
+	const Elf_Shdr *hdr;
+	const char *hdrname;
+	int i;
+
+	for (hdr = shdr0, i = 0; i < nhdr; hdr = &shdr0[++i]) {
+		if (w(hdr->sh_type) != type)
+			continue;
+
+		/* If we are just looking for a section by type (ie. SYMTAB) */
+		if (!name)
+			return hdr;
+
+		hdrname = &shstrtab[w(hdr->sh_name)];
+		if (strcmp(hdrname, name) == 0)
+			return hdr;
+	}
+	return NULL;
+}
+
+static void
+FUNC(section_update)(const Elf_Ehdr *ehdr, const Elf_Shdr *symhdr,
+		     unsigned shtype, const Elf_Rel *rel, void *data)
+{
+	const Elf_Shdr *shdr0 = get_shdr(ehdr);
+	const Elf_Shdr *targethdr;
+	const Elf_Rela *rela;
+	const Elf_Sym *syment;
+	uint_t offset = _w(rel->r_offset);
+	uint_t info = _w(rel->r_info);
+	uint_t sym = ELF_R_SYM(info);
+	uint_t type = ELF_R_TYPE(info);
+	uint_t addend;
+	uint_t targetloc;
+
+	if (shtype == SHT_RELA) {
+		rela = (const Elf_Rela *)rel;
+		addend = _w(rela->r_addend);
+	} else
+		addend = _w(*(int *)(data + offset));
+
+	syment = (const Elf_Sym *)get_section_loc(ehdr, symhdr);
+	targethdr = &shdr0[w2(syment[sym].st_shndx)];
+	targetloc = _w(targethdr->sh_offset);
+
+	/* TODO, need a separate function for all archs */
+	if (type != R_386_32)
+		die(NULL, "Arch relocation type %d not supported", type);
+
+	targetloc += addend;
+
+#if 0
+	printf("offset=%x target=%x shoffset=%x add=%x indx=%x\n",
+	       offset, targetloc, _w(targethdr->sh_offset), addend,
+	       targetloc - _w(targethdr->sh_offset));
+#endif
+	*(uint_t *)(data + offset) = targetloc;
+}
+
+/* Overall supervision for Elf32 ET_REL file. */
+static void
+FUNC(do_func)(Elf_Ehdr *ehdr, char const *const fname, unsigned const reltype)
+{
+	const Elf_Shdr *jlshdr;
+	const Elf_Shdr *jlrhdr;
+	const Elf_Shdr *symhdr;
+	const Elf_Rel *rel;
+	unsigned size;
+	unsigned cnt;
+	unsigned i;
+	uint_t type;
+	void *jdata;
+	void *data;
+
+	jlshdr = FUNC(find_shdr)(ehdr, "__jump_table", SHT_PROGBITS);
+	if (!jlshdr)
+		return;
+
+	jlrhdr = FUNC(find_relhdr)(ehdr, jlshdr);
+	if (!jlrhdr)
+		return;
+
+	/*
+	 * Create and fill in the __jump_table section and use it to
+	 * find the offsets into the text that we want to update.
+	 * We create it so that we do not depend on the order of the
+	 * relocations, and use the table directly, as it is broken
+	 * up into sections.
+	 */
+	size = _w(jlshdr->sh_size);
+	data = umalloc(size);
+
+	jdata = (void *)get_section_loc(ehdr, jlshdr);
+	memcpy(data, jdata, size);
+
+	cnt = _w(jlrhdr->sh_size) / w(jlrhdr->sh_entsize);
+
+	rel = (const Elf_Rel *)get_section_loc(ehdr, jlrhdr);
+
+	/* Is this as Rel or Rela? */
+	type = w(jlrhdr->sh_type);
+
+	symhdr = FUNC(find_shdr)(ehdr, NULL, SHT_SYMTAB);
+
+	for (i = 0; i < cnt; i++) {
+		FUNC(section_update)(ehdr, symhdr, type, rel, data);
+		rel = (void *)rel + w(jlrhdr->sh_entsize);
+	}
+
+	/*
+	 * This is specific to x86. The jump_table is stored in three
+	 * long words. The first is the location of the jmp target we
+	 * must update.
+	 */
+	cnt = size / sizeof(uint_t);
+
+	for (i = 0; i < cnt; i += 3)
+		make_nop((void *)ehdr, *(uint_t *)(data + i * sizeof(uint_t)));
+
+	free(data);
+}
-- 
1.7.8.3


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