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126 lines
2.6 KiB
126 lines
2.6 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* vdso_test.c: Sample code to test parse_vdso.c on x86 |
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* Copyright (c) 2011-2014 Andy Lutomirski |
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* |
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* You can amuse yourself by compiling with: |
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* gcc -std=gnu99 -nostdlib |
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* -Os -fno-asynchronous-unwind-tables -flto -lgcc_s |
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* vdso_standalone_test_x86.c parse_vdso.c |
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* to generate a small binary. On x86_64, you can omit -lgcc_s |
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* if you want the binary to be completely standalone. |
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*/ |
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#include <sys/syscall.h> |
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#include <sys/time.h> |
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#include <unistd.h> |
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#include <stdint.h> |
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#include "parse_vdso.h" |
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/* We need a libc functions... */ |
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int strcmp(const char *a, const char *b) |
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{ |
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/* This implementation is buggy: it never returns -1. */ |
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while (*a || *b) { |
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if (*a != *b) |
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return 1; |
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if (*a == 0 || *b == 0) |
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return 1; |
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a++; |
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b++; |
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} |
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return 0; |
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} |
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/* ...and two syscalls. This is x86-specific. */ |
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static inline long x86_syscall3(long nr, long a0, long a1, long a2) |
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{ |
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long ret; |
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#ifdef __x86_64__ |
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asm volatile ("syscall" : "=a" (ret) : "a" (nr), |
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"D" (a0), "S" (a1), "d" (a2) : |
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"cc", "memory", "rcx", |
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"r8", "r9", "r10", "r11" ); |
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#else |
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asm volatile ("int $0x80" : "=a" (ret) : "a" (nr), |
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"b" (a0), "c" (a1), "d" (a2) : |
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"cc", "memory" ); |
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#endif |
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return ret; |
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} |
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static inline long linux_write(int fd, const void *data, size_t len) |
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{ |
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return x86_syscall3(__NR_write, fd, (long)data, (long)len); |
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} |
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static inline void linux_exit(int code) |
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{ |
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x86_syscall3(__NR_exit, code, 0, 0); |
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} |
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void to_base10(char *lastdig, time_t n) |
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{ |
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while (n) { |
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*lastdig = (n % 10) + '0'; |
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n /= 10; |
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lastdig--; |
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} |
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} |
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__attribute__((externally_visible)) void c_main(void **stack) |
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{ |
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/* Parse the stack */ |
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long argc = (long)*stack; |
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stack += argc + 2; |
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/* Now we're pointing at the environment. Skip it. */ |
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while(*stack) |
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stack++; |
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stack++; |
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/* Now we're pointing at auxv. Initialize the vDSO parser. */ |
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vdso_init_from_auxv((void *)stack); |
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/* Find gettimeofday. */ |
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typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz); |
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gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday"); |
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if (!gtod) |
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linux_exit(1); |
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struct timeval tv; |
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long ret = gtod(&tv, 0); |
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if (ret == 0) { |
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char buf[] = "The time is .000000\n"; |
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to_base10(buf + 31, tv.tv_sec); |
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to_base10(buf + 38, tv.tv_usec); |
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linux_write(1, buf, sizeof(buf) - 1); |
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} else { |
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linux_exit(ret); |
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} |
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linux_exit(0); |
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} |
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/* |
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* This is the real entry point. It passes the initial stack into |
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* the C entry point. |
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*/ |
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asm ( |
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".text\n" |
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".global _start\n" |
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".type _start,@function\n" |
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"_start:\n\t" |
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#ifdef __x86_64__ |
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"mov %rsp,%rdi\n\t" |
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"jmp c_main" |
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#else |
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"push %esp\n\t" |
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"call c_main\n\t" |
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"int $3" |
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#endif |
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);
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