Execute syscall in other process

tracexecv2.c

#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <sys/ptrace.h>
#include <sys/syscall.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/user.h>
#include <sys/wait.h>

long try_(long err, const char * cmd, int line) {
    if (err < 0 && errno != 0) {
        printf("line : %d\n", line);
        perror(cmd);
        exit(1);
    }
    return err;
}

#define try(x) try_(x, #x, __LINE__)

#ifdef __amd64__
typedef struct user_regs_struct regs_struct;
#define IP(regs) regs.rip
#define SP(regs) regs.rsp
#define SYSCALL_RESULT(regs) regs.rax
#endif

#ifdef __arm__
typedef struct user_regs regs_struct;
#define IP(regs) regs.uregs[15]
#define SP(regs) regs.uregs[13]
#define SYSCALL_RESULT(regs) regs.uregs[0]
#endif

#define ALIGN(addr) ((addr) & ~(sizeof(long)-1))

long tsyscall(pid_t pid, long number, ...) {
    long asm_orig;
    va_list ap;
    regs_struct regs_orig, regs;
    try(ptrace(PTRACE_GETREGS, pid, 0, &regs_orig));
    regs = regs_orig;
    va_start(ap, number);
#ifdef __amd64__
    static uint8_t asm_syscall[8] __attribute__ ((aligned (8))) = { /*syscall*/ 0x0f, 0x05, /* ud2 */ 0x0f, 0x0b, 0, 0, 0, 0};
    regs.rax = number;
    regs.rdi = va_arg(ap, long);
    regs.rsi = va_arg(ap, long);
    regs.rdx = va_arg(ap, long);
    regs.r10 = va_arg(ap, long);
    regs.r8 = va_arg(ap, long);
    regs.r9 = va_arg(ap, long);
#endif
#ifdef __arm__
    static uint8_t asm_syscall[8] __attribute__ ((aligned (4))) = { /*swi 0*/ 0x00, 0xdf, /* illegal */ 0x00, 0xde };
    regs.uregs[7] = number;
    regs.uregs[0] = va_arg(ap, long);
    regs.uregs[1] = va_arg(ap, long);
    regs.uregs[2] = va_arg(ap, long);
    regs.uregs[3] = va_arg(ap, long);
    regs.uregs[4] = va_arg(ap, long);
    regs.uregs[5] = va_arg(ap, long);
    regs.uregs[6] = va_arg(ap, long);
#endif
    assert(sizeof(asm_orig) == sizeof(asm_syscall));
    va_end(ap);
    IP(regs) = ALIGN(IP(regs_orig));
    void * ip = (void*)IP(regs);
    errno = 0; /* must do this for error checking in peektext */
    asm_orig = try(ptrace(PTRACE_PEEKTEXT, pid, ip, 0));
    try(ptrace(PTRACE_SETREGS, pid, 0, &regs));
    try(ptrace(PTRACE_POKETEXT, pid, ip, *(long*)asm_syscall));
    try(ptrace(PTRACE_SINGLESTEP, pid, 0, 0));
    int wstatus;
    try(waitpid(pid, &wstatus, 0));
    if (WIFEXITED(wstatus)) return WEXITSTATUS(wstatus);
    try(ptrace(PTRACE_GETREGS, pid, 0, &regs));
    try(ptrace(PTRACE_POKETEXT, pid, ip, asm_orig));
    try(ptrace(PTRACE_SETREGS, pid, 0, &regs_orig));
    return SYSCALL_RESULT(regs);
}

pid_t pid;

void onexit() {
    kill(pid, SIGKILL);
    kill(pid, SIGCONT);
}

int main() {
    pid = try(fork());
    atexit(onexit);
    if (pid == 0) {
        raise(SIGSTOP);
        return 1;
    }
    try(ptrace(PTRACE_SEIZE, pid, 0, 0));
    waitpid(pid, 0, 0);
    pid_t p = tsyscall(pid, __NR_getpid);
    printf("PID: %d %d\n", pid, p);
    try(ptrace(PTRACE_DETACH, pid, 0, SIGCONT));
}