[PATCH][RFC] jump_labels/x86: Use either 5 byte or 2 byte jumps

Steven Rostedt
2011-10-07T17:09:37Z

Note, this is just hacked together and needs to be cleaned up. Please do
not comment on formatting or other sloppiness of this patch. I know it's
sloppy and I left debug statements in. I want the comments to be on the
idea of the patch.

I created a new file called scripts/update_jump_label.[ch] based on some
of the work of recordmcount.c. This is executed at build time on all
object files just like recordmcount is. But it does not add any new
sections, it just modifies the code at build time to convert all jump
labels into nops.

The idea is in arch/x86/include/asm/jump_label.h to not place a nop, but
instead to insert a jmp to the label. Depending on how gcc optimizes the
code, the jmp will be either end up being a 2 byte or 5 byte jump.

After an object is compiled, update_jump_label is executed on this file
and it reads the ELF relocation table to find the jump label locations
and examines what jump was used. It then converts the jump into either a
2 byte or 5 byte nop that is appropriate.

At boot time, the jump labels no longer need to be converted (although
we may do so in the future to use better nops depending on the machine
that is used). When jump labels are enabled, the code is examined to see
if a two byte or 5 byte version was used, and the appropriate update is
made.

I just booted this patch and it worked. I was able to enable and disable
trace points using jump labels. Benchmarks are welcomed :)

Comments and thoughts?

-- Steve

Sloppy-signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/Makefile b/Makefile
index 31f967c..8368f42 100644
--- a/Makefile
+++ b/Makefile
@@ -245,7 +245,7 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \

HOSTCC = gcc
HOSTCXX = g++
-HOSTCFLAGS = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer
+HOSTCFLAGS = -Wall -Wmissing-prototypes -Wstrict-prototypes -g -fomit-frame-pointer
HOSTCXXFLAGS = -O2

# Decide whether to build built-in, modular, or both.
@@ -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/arch/x86/Kconfig b/arch/x86/Kconfig
index 6a47bb2..6de726a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -61,6 +61,7 @@ config X86
select HAVE_ARCH_KMEMCHECK
select HAVE_USER_RETURN_NOTIFIER
select HAVE_ARCH_JUMP_LABEL
+ select HAVE_BUILD_TIME_JUMP_LABEL
select HAVE_TEXT_POKE_SMP
select HAVE_GENERIC_HARDIRQS
select HAVE_SPARSE_IRQ
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index a32b18c..872b3e1 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -14,7 +14,7 @@
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
asm goto("1:"
- JUMP_LABEL_INITIAL_NOP
+ "jmp %l[l_yes]\n"
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
_ASM_PTR "1b, %l[l_yes], %c0 \n\t"
diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 3fee346..1f7f88f 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -16,34 +16,75 @@

#ifdef HAVE_JUMP_LABEL

+static unsigned char nop_short[] = { P6_NOP2 };
+
union jump_code_union {
char code[JUMP_LABEL_NOP_SIZE];
struct {
char jump;
int offset;
} __attribute__((packed));
+ struct {
+ char jump_short;
+ char offset_short;
+ } __attribute__((packed));
};

void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type)
{
union jump_code_union code;
+ unsigned char op;
+ unsigned size;
+ unsigned char nop;
+
+ /* Use probe_kernel_read()? */
+ op = *(unsigned char *)entry->code;
+ nop = ideal_nops[NOP_ATOMIC5][0];

if (type == JUMP_LABEL_ENABLE) {
- code.jump = 0xe9;
- code.offset = entry->target -
- (entry->code + JUMP_LABEL_NOP_SIZE);
- } else
- memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
+ if (op == 0xe9 || op == 0xeb)
+ /* Already enabled. Warn? */
+ return;
+
+ /* FIXME for all archs */
+ if (op == nop_short[0]) {
+ size = 2;
+ code.jump_short = 0xeb;
+ code.offset = entry->target -
+ (entry->code + 2);
+ /* Check for overflow ? */
+ } else if (op == nop) {
+ size = JUMP_LABEL_NOP_SIZE;
+ code.jump = 0xe9;
+ code.offset = entry->target - (entry->code + size);
+ } else
+ return; /* WARN ? */
+
+ } else {
+ if (op == nop_short[0] || nop)
+ /* Already disabled, warn? */
+ return;
+
+ if (op == 0xe9) {
+ size = JUMP_LABEL_NOP_SIZE;
+ memcpy(&code, ideal_nops[NOP_ATOMIC5], size);
+ } else if (op == 0xeb) {
+ size = 2;
+ memcpy(&code, nop_short, size);
+ } else
+ return; /* WARN ? */
+ }
get_online_cpus();
mutex_lock(&text_mutex);
- text_poke_smp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
+ text_poke_smp((void *)entry->code, &code, size);
mutex_unlock(&text_mutex);
put_online_cpus();
}

void arch_jump_label_text_poke_early(jump_label_t addr)
{
+ return;
text_poke_early((void *)addr, ideal_nops[NOP_ATOMIC5],
JUMP_LABEL_NOP_SIZE);
}
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 a0fd502..bc0d89b 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..86e17bc
--- /dev/null
+++ b/scripts/update_jump_label.c
@@ -0,0 +1,349 @@
+/*
+ * update_jump_label.c: replace jmps with nops at compile time.
+ * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
+ * Parsing of the elf file was influenced by recordmcount.c
+ * originally written by and copyright to John F. Reiser <jreiser@BitWagon.com>.
+ */
+
+/*
+ * 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, 0x99 };
+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\n");
+ }
+
+ /* 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);
+
+ if (w2(ehdr->e_machine) == EM_S390) {
+ reltype = R_390_32;
+ }
+ if (w2(ehdr->e_machine) == EM_MIPS) {
+ reltype = R_MIPS_32;
+ }
+ 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);
+
+ if (w2(ghdr->e_machine) == EM_S390)
+ reltype = R_390_64;
+
+#if 0
+ if (w2(ghdr->e_machine) == EM_MIPS) {
+ reltype = R_MIPS_64;
+ Elf64_r_sym = MIPS64_r_sym;
+ }
+#endif
+ 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..6ff9846
--- /dev/null
+++ b/scripts/update_jump_label.h
@@ -0,0 +1,322 @@
+/*
+ * recordmcount.h
+ *
+ * This code was taken out of recordmcount.c written by
+ * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>. 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@redhat.com>, 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. */
+
+#if 0
+static uint_t FUNC(fn_ELF_R_SYM)(Elf_Rel const *rp)
+{
+ return ELF_R_SYM(_w(rp->r_info));
+}
+static uint_t (*FUNC(Elf_r_sym))(Elf_Rel const *rp) = FUNC(fn_ELF_R_SYM);
+#endif
+
+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);
+ }
+}
+
+/* Evade ISO C restriction: no declaration after statement in has_rel_mcount. */
+static char const *
+FUNC(__has_rel_jump_table)(Elf_Shdr const *const relhdr, /* is SHT_REL or SHT_RELA */
+ Elf_Shdr const *const shdr0,
+ char const *const shstrtab,
+ char const *const fname)
+{
+ /* .sh_info depends on .sh_type == SHT_REL[,A] */
+ Elf_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
+ char const *const txtname = &shstrtab[w(txthdr->sh_name)];
+
+ if (strcmp("__jump_table", txtname) == 0) {
+ fprintf(stderr, "warning: __mcount_loc already exists: %s\n",
+ fname);
+// succeed_file();
+ }
+ if (w(txthdr->sh_type) != SHT_PROGBITS ||
+ !(w(txthdr->sh_flags) & SHF_EXECINSTR))
+ return NULL;
+ return txtname;
+}
+
+static char const *FUNC(has_rel_jump_table)(Elf_Shdr const *const relhdr,
+ Elf_Shdr const *const shdr0,
+ char const *const shstrtab,
+ char const *const fname)
+{
+ if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
+ return NULL;
+ return FUNC(__has_rel_jump_table)(relhdr, shdr0, shstrtab, fname);
+}
+
+/* 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(*(unsigned short *)(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 1
+ printf("offset=%x target=%x shoffset=%x add=%x\n",
+ offset, targetloc, _w(targethdr->sh_offset), addend);
+#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)
+ if (0)make_nop((void *)ehdr, *(uint_t *)(data + i * sizeof(uint_t)));
+
+ free(data);
+}