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![Heiko Carstens](/assets/img/avatar_default.png)
If the function tracer is enabled, allow to set kprobes on the first instruction of a function (which is the function trace caller): If no kprobe is set handling of enabling and disabling function tracing of a function simply patches the first instruction. Either it is a nop (right now it's an unconditional branch, which skips the mcount block), or it's a branch to the ftrace_caller() function. If a kprobe is being placed on a function tracer calling instruction we encode if we actually have a nop or branch in the remaining bytes after the breakpoint instruction (illegal opcode). This is possible, since the size of the instruction used for the nop and branch is six bytes, while the size of the breakpoint is only two bytes. Therefore the first two bytes contain the illegal opcode and the last four bytes contain either "0" for nop or "1" for branch. The kprobes code will then execute/simulate the correct instruction. Instruction patching for kprobes and function tracer is always done with stop_machine(). Therefore we don't have any races where an instruction is patched concurrently on a different cpu. Besides that also the program check handler which executes the function trace caller instruction won't be executed concurrently to any stop_machine() execution. This allows to keep full fault based kprobes handling which generates correct pt_regs contents automatically. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
485 lines
12 KiB
C
485 lines
12 KiB
C
/*
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* recordmcount.c: construct a table of the locations of calls to 'mcount'
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* so that ftrace can find them quickly.
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* Copyright 2009 John F. Reiser <jreiser@BitWagon.com>. All rights reserved.
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* Licensed under the GNU General Public License, version 2 (GPLv2).
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*
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* Restructured to fit Linux format, as well as other updates:
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* Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
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*/
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/*
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* Strategy: alter the .o file in-place.
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*
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* Append a new STRTAB that has the new section names, followed by a new array
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* ElfXX_Shdr[] that has the new section headers, followed by the section
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* contents for __mcount_loc and its relocations. The old shstrtab strings,
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* and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
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* kilobytes.) Subsequent processing by /bin/ld (or the kernel module loader)
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* will ignore the garbage regions, because they are not designated by the
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* new .e_shoff nor the new ElfXX_Shdr[]. [In order to remove the garbage,
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* then use "ld -r" to create a new file that omits the garbage.]
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*/
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#include <sys/types.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <getopt.h>
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#include <elf.h>
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#include <fcntl.h>
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#include <setjmp.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#ifndef EM_METAG
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/* Remove this when these make it to the standard system elf.h. */
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#define EM_METAG 174
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#define R_METAG_ADDR32 2
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#define R_METAG_NONE 3
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#endif
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#ifndef EM_AARCH64
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#define EM_AARCH64 183
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#define R_AARCH64_ABS64 257
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#endif
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static int fd_map; /* File descriptor for file being modified. */
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static int mmap_failed; /* Boolean flag. */
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static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
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static char gpfx; /* prefix for global symbol name (sometimes '_') */
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static struct stat sb; /* Remember .st_size, etc. */
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static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
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static const char *altmcount; /* alternate mcount symbol name */
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static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
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/* setjmp() return values */
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enum {
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SJ_SETJMP = 0, /* hardwired first return */
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SJ_FAIL,
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SJ_SUCCEED
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};
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/* Per-file resource cleanup when multiple files. */
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static void
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cleanup(void)
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{
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if (!mmap_failed)
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munmap(ehdr_curr, sb.st_size);
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else
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free(ehdr_curr);
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close(fd_map);
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}
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static void __attribute__((noreturn))
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fail_file(void)
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{
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cleanup();
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longjmp(jmpenv, SJ_FAIL);
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}
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static void __attribute__((noreturn))
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succeed_file(void)
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{
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cleanup();
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longjmp(jmpenv, SJ_SUCCEED);
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}
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/* ulseek, uread, ...: Check return value for errors. */
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static off_t
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ulseek(int const fd, off_t const offset, int const whence)
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{
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off_t const w = lseek(fd, offset, whence);
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if (w == (off_t)-1) {
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perror("lseek");
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fail_file();
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}
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return w;
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}
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static size_t
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uread(int const fd, void *const buf, size_t const count)
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{
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size_t const n = read(fd, buf, count);
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if (n != count) {
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perror("read");
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fail_file();
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}
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return n;
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}
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static size_t
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uwrite(int const fd, void const *const buf, size_t const count)
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{
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size_t const n = write(fd, buf, count);
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if (n != count) {
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perror("write");
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fail_file();
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}
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return n;
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}
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static void *
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umalloc(size_t size)
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{
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void *const addr = malloc(size);
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if (addr == 0) {
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fprintf(stderr, "malloc failed: %zu bytes\n", size);
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fail_file();
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}
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return addr;
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}
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static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
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static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
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static unsigned char *ideal_nop;
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static char rel_type_nop;
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static int (*make_nop)(void *map, size_t const offset);
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static int make_nop_x86(void *map, size_t const offset)
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{
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uint32_t *ptr;
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unsigned char *op;
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/* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
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ptr = map + offset;
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if (*ptr != 0)
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return -1;
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op = map + offset - 1;
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if (*op != 0xe8)
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return -1;
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/* convert to nop */
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ulseek(fd_map, offset - 1, SEEK_SET);
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uwrite(fd_map, ideal_nop, 5);
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return 0;
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}
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/*
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* Get the whole file as a programming convenience in order to avoid
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* malloc+lseek+read+free of many pieces. If successful, then mmap
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* avoids copying unused pieces; else just read the whole file.
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* Open for both read and write; new info will be appended to the file.
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* Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
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* do not propagate to the file until an explicit overwrite at the last.
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* This preserves most aspects of consistency (all except .st_size)
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* for simultaneous readers of the file while we are appending to it.
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* However, multiple writers still are bad. We choose not to use
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* locking because it is expensive and the use case of kernel build
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* makes multiple writers unlikely.
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*/
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static void *mmap_file(char const *fname)
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{
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void *addr;
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fd_map = open(fname, O_RDWR);
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if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
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perror(fname);
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fail_file();
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}
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if (!S_ISREG(sb.st_mode)) {
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fprintf(stderr, "not a regular file: %s\n", fname);
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fail_file();
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}
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addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
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fd_map, 0);
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mmap_failed = 0;
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if (addr == MAP_FAILED) {
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mmap_failed = 1;
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addr = umalloc(sb.st_size);
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uread(fd_map, addr, sb.st_size);
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}
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return addr;
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}
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/* w8rev, w8nat, ...: Handle endianness. */
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static uint64_t w8rev(uint64_t const x)
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{
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return ((0xff & (x >> (0 * 8))) << (7 * 8))
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| ((0xff & (x >> (1 * 8))) << (6 * 8))
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| ((0xff & (x >> (2 * 8))) << (5 * 8))
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| ((0xff & (x >> (3 * 8))) << (4 * 8))
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| ((0xff & (x >> (4 * 8))) << (3 * 8))
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| ((0xff & (x >> (5 * 8))) << (2 * 8))
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| ((0xff & (x >> (6 * 8))) << (1 * 8))
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| ((0xff & (x >> (7 * 8))) << (0 * 8));
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}
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static uint32_t w4rev(uint32_t const x)
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{
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return ((0xff & (x >> (0 * 8))) << (3 * 8))
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| ((0xff & (x >> (1 * 8))) << (2 * 8))
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| ((0xff & (x >> (2 * 8))) << (1 * 8))
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| ((0xff & (x >> (3 * 8))) << (0 * 8));
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}
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static uint32_t w2rev(uint16_t const x)
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{
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return ((0xff & (x >> (0 * 8))) << (1 * 8))
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| ((0xff & (x >> (1 * 8))) << (0 * 8));
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}
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static uint64_t w8nat(uint64_t const x)
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{
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return x;
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}
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static uint32_t w4nat(uint32_t const x)
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{
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return x;
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}
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static uint32_t w2nat(uint16_t const x)
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{
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return x;
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}
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static uint64_t (*w8)(uint64_t);
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static uint32_t (*w)(uint32_t);
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static uint32_t (*w2)(uint16_t);
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/* Names of the sections that could contain calls to mcount. */
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static int
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is_mcounted_section_name(char const *const txtname)
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{
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return strcmp(".text", txtname) == 0 ||
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strcmp(".ref.text", txtname) == 0 ||
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strcmp(".sched.text", txtname) == 0 ||
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strcmp(".spinlock.text", txtname) == 0 ||
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strcmp(".irqentry.text", txtname) == 0 ||
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strcmp(".kprobes.text", txtname) == 0 ||
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strcmp(".text.unlikely", txtname) == 0;
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}
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/* 32 bit and 64 bit are very similar */
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#include "recordmcount.h"
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#define RECORD_MCOUNT_64
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#include "recordmcount.h"
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/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
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* http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
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* We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
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* to imply the order of the members; the spec does not say so.
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* typedef unsigned char Elf64_Byte;
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* fails on MIPS64 because their <elf.h> already has it!
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*/
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typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
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union mips_r_info {
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Elf64_Xword r_info;
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struct {
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Elf64_Word r_sym; /* Symbol index. */
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myElf64_Byte r_ssym; /* Special symbol. */
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myElf64_Byte r_type3; /* Third relocation. */
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myElf64_Byte r_type2; /* Second relocation. */
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myElf64_Byte r_type; /* First relocation. */
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} r_mips;
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};
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static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
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{
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return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
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}
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static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
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{
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rp->r_info = ((union mips_r_info){
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.r_mips = { .r_sym = w(sym), .r_type = type }
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}).r_info;
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}
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static void
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do_file(char const *const fname)
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{
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Elf32_Ehdr *const ehdr = mmap_file(fname);
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unsigned int reltype = 0;
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ehdr_curr = ehdr;
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w = w4nat;
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w2 = w2nat;
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w8 = w8nat;
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switch (ehdr->e_ident[EI_DATA]) {
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static unsigned int const endian = 1;
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default:
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fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
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ehdr->e_ident[EI_DATA], fname);
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fail_file();
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break;
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case ELFDATA2LSB:
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if (*(unsigned char const *)&endian != 1) {
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/* main() is big endian, file.o is little endian. */
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w = w4rev;
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w2 = w2rev;
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w8 = w8rev;
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}
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break;
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case ELFDATA2MSB:
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if (*(unsigned char const *)&endian != 0) {
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/* main() is little endian, file.o is big endian. */
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w = w4rev;
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w2 = w2rev;
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w8 = w8rev;
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}
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break;
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} /* end switch */
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if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
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|| w2(ehdr->e_type) != ET_REL
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|| ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
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fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
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fail_file();
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}
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gpfx = 0;
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switch (w2(ehdr->e_machine)) {
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default:
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fprintf(stderr, "unrecognized e_machine %d %s\n",
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w2(ehdr->e_machine), fname);
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fail_file();
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break;
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case EM_386:
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reltype = R_386_32;
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make_nop = make_nop_x86;
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ideal_nop = ideal_nop5_x86_32;
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mcount_adjust_32 = -1;
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break;
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case EM_ARM: reltype = R_ARM_ABS32;
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altmcount = "__gnu_mcount_nc";
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break;
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case EM_AARCH64:
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reltype = R_AARCH64_ABS64; gpfx = '_'; break;
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case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
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case EM_METAG: reltype = R_METAG_ADDR32;
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altmcount = "_mcount_wrapper";
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rel_type_nop = R_METAG_NONE;
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/* We happen to have the same requirement as MIPS */
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is_fake_mcount32 = MIPS32_is_fake_mcount;
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break;
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case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
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case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
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case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
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case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
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case EM_SH: reltype = R_SH_DIR32; break;
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case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
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case EM_X86_64:
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make_nop = make_nop_x86;
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ideal_nop = ideal_nop5_x86_64;
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reltype = R_X86_64_64;
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mcount_adjust_64 = -1;
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break;
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} /* end switch */
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switch (ehdr->e_ident[EI_CLASS]) {
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default:
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fprintf(stderr, "unrecognized ELF class %d %s\n",
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ehdr->e_ident[EI_CLASS], fname);
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fail_file();
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break;
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case ELFCLASS32:
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if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
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|| w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
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fprintf(stderr,
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"unrecognized ET_REL file: %s\n", fname);
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fail_file();
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}
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if (w2(ehdr->e_machine) == EM_MIPS) {
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reltype = R_MIPS_32;
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is_fake_mcount32 = MIPS32_is_fake_mcount;
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}
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do32(ehdr, fname, reltype);
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break;
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case ELFCLASS64: {
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Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
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if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
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|| w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
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fprintf(stderr,
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"unrecognized ET_REL file: %s\n", fname);
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fail_file();
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}
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if (w2(ghdr->e_machine) == EM_S390) {
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reltype = R_390_64;
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mcount_adjust_64 = -14;
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}
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if (w2(ghdr->e_machine) == EM_MIPS) {
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reltype = R_MIPS_64;
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Elf64_r_sym = MIPS64_r_sym;
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Elf64_r_info = MIPS64_r_info;
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is_fake_mcount64 = MIPS64_is_fake_mcount;
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}
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do64(ghdr, fname, reltype);
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break;
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}
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} /* end switch */
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cleanup();
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}
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int
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main(int argc, char *argv[])
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{
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const char ftrace[] = "/ftrace.o";
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int ftrace_size = sizeof(ftrace) - 1;
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int n_error = 0; /* gcc-4.3.0 false positive complaint */
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int c;
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int i;
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while ((c = getopt(argc, argv, "w")) >= 0) {
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switch (c) {
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case 'w':
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warn_on_notrace_sect = 1;
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break;
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default:
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fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
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return 0;
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}
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}
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if ((argc - optind) < 1) {
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fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
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return 0;
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}
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/* Process each file in turn, allowing deep failure. */
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for (i = optind; i < argc; i++) {
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char *file = argv[i];
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int const sjval = setjmp(jmpenv);
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int len;
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/*
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* The file kernel/trace/ftrace.o references the mcount
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* function but does not call it. Since ftrace.o should
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* not be traced anyway, we just skip it.
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*/
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len = strlen(file);
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if (len >= ftrace_size &&
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strcmp(file + (len - ftrace_size), ftrace) == 0)
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continue;
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|
|
switch (sjval) {
|
|
default:
|
|
fprintf(stderr, "internal error: %s\n", file);
|
|
exit(1);
|
|
break;
|
|
case SJ_SETJMP: /* normal sequence */
|
|
/* Avoid problems if early cleanup() */
|
|
fd_map = -1;
|
|
ehdr_curr = NULL;
|
|
mmap_failed = 1;
|
|
do_file(file);
|
|
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;
|
|
}
|