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![Wu Zhangjin](/assets/img/avatar_default.png)
Since MIPS modules' address space differs from the core kernel space, to access the _mcount in the core kernel, the kernel functions in modules must use long call (-mlong-calls): load the _mcount address into one register and jump to the address stored by the register: c: 3c030000 lui v1,0x0 <--------> b label c: R_MIPS_HI16 _mcount c: R_MIPS_NONE *ABS* c: R_MIPS_NONE *ABS* 10: 64630000 daddiu v1,v1,0 10: R_MIPS_LO16 _mcount 10: R_MIPS_NONE *ABS* 10: R_MIPS_NONE *ABS* 14: 03e0082d move at,ra 18: 0060f809 jalr v1 label: In the old Perl version of recordmcount, we only need to record the position of the 1st R_MIPS_HI16 type of _mcount, and later, in ftrace_make_nop(), replace the instruction in this position by a "b label" and in ftrace_make_call(), replace it back. But, the default C version of recordmcount records all of the _mcount symbols, so, we must filter the 2nd _mcount like the Perl version of recordmcount does. The C version of recordmcount copes with the symbols before they are linked, So It doesn't know the type of the symbols and therefore can not filter the symbols as the Perl version of recordmcount does. But as we can see above, the 2nd _mcount symbols of the long call alawys follows the 1st _mcount symbol of the same long call, which means the offset from the 1st to the 2nd is fixed, it is 0x10-0xc = 4 here, 4 is the length of the 1st load instruciton, for MIPS has fixed length of instructions, this offset is always 4. And as we know, the _mcount is inserted into the entry of every kernel function, the offset between the other _mcount's is expected to be always bigger than 4. So, to filter the 2ns _mcount symbol of the long call, we can simply check the offset between two _mcount symbols, If it is 4, then, filter the 2nd _mcount symbol. To avoid touching too much code, an 'empty' function fn_is_fake_mcount() is added for all of the archs, and the specific archs can override it via chaning the function pointer: is_fake_mcount in do_file() with the e_machine. e.g. This patch adds MIPS_is_fake_mcount() to override the default fn_is_fake_mcount() pointed by is_fake_mcount. This fn_is_fake_mcount() checks if the _mcount symbol is fake, e.g. the 2nd _mcount symbol of the long call is fake, for there are 2 _mcount symbols mapped to one real mcount call, so, one of them is fake and must be filtered. This fn_is_fake_mcount() is called in sift_rel_mcount() after finding the _mcount symbols and before adding the _mcount symbol into mrelp, so, it can prevent the fake mcount symbol going into the last __mcount_loc table. Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com> LKML-Reference: <b866f0138224340a132d31861fa3f9300dee30ac.1288176026.git.wuzhangjin@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
407 lines
11 KiB
C
407 lines
11 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 <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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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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/* 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 ((off_t)-1 == w) {
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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 (0 == addr) {
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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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/*
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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 (0 > fd_map || 0 > fstat(fd_map, &sb)) {
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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 (MAP_FAILED == addr) {
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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 0 == strcmp(".text", txtname) ||
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0 == strcmp(".sched.text", txtname) ||
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0 == strcmp(".spinlock.text", txtname) ||
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0 == strcmp(".irqentry.text", txtname) ||
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0 == strcmp(".text.unlikely", txtname);
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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 (1 != *(unsigned char const *)&endian) {
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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 (0 != *(unsigned char const *)&endian) {
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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 (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
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|| ET_REL != w2(ehdr->e_type)
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|| EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
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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: reltype = R_386_32; break;
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case EM_ARM: reltype = R_ARM_ABS32; break;
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case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; 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: reltype = R_X86_64_64; 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 (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
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|| sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
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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 (EM_S390 == w2(ehdr->e_machine))
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reltype = R_390_32;
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if (EM_MIPS == w2(ehdr->e_machine)) {
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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 (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
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|| sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
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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 (EM_S390 == w2(ghdr->e_machine))
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reltype = R_390_64;
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if (EM_MIPS == w2(ghdr->e_machine)) {
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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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} /* end switch */
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cleanup();
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}
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int
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main(int argc, char const *argv[])
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{
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const char ftrace[] = "kernel/trace/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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if (argc <= 1) {
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fprintf(stderr, "usage: recordmcount 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 (--argc, ++argv; 0 < argc; --argc, ++argv) {
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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(argv[0]);
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if (len >= ftrace_size &&
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strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
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continue;
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switch (sjval) {
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default: {
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fprintf(stderr, "internal error: %s\n", argv[0]);
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exit(1);
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} break;
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case SJ_SETJMP: { /* normal sequence */
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/* Avoid problems if early cleanup() */
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fd_map = -1;
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ehdr_curr = NULL;
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mmap_failed = 1;
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do_file(argv[0]);
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} break;
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case SJ_FAIL: { /* error in do_file or below */
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++n_error;
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} break;
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case SJ_SUCCEED: { /* premature success */
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/* do nothing */
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} break;
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} /* end switch */
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}
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return !!n_error;
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}
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