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    SubjectRe: Current utrace breaks UML
    On Tue, May 22, 2007 at 11:46:11PM -0700, Roland McGrath wrote:
    > Do you have a test case for PTRACE_SYSEMU that does not work right?

    UML, obviously. Below is a smaller test. orig_eax is wrong, so you
    can't read the system call number from the process.

    With kernel-2.6.20-1.2948, it prints out a bunch of -1's. On FC5
    kernels, you get more reasonable numbers.

    Jeff

    --
    Work email - jdike at linux dot intel dot com


    #include <stdlib.h>
    #include <stdio.h>
    #include <asm/unistd.h>
    #include <sys/mman.h>
    #include <sys/ptrace.h>
    #include <asm/ptrace.h>
    #include <sys/wait.h>

    #define PTRACE_SYSEMU 31
    #define PAGE_SIZE 4096

    static inline long stub_syscall0(long syscall)
    {
    long ret;

    __asm__ volatile ("int $0x80" : "=a" (ret) : "0" (syscall));

    return ret;
    }

    static void child(void)
    {
    if(ptrace(PTRACE_TRACEME, 0, 0, 0) < 0){
    perror("traceme");
    exit(1);
    }

    kill(getpid(), SIGUSR1);
    stub_syscall0(__NR_getpid);
    }

    int main(void)
    {
    void *stack;
    unsigned long sp, regs[FRAME_SIZE];
    int pid, n, status;

    stack = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    if(stack == MAP_FAILED){
    perror("mmap");
    exit(1);
    }

    sp = (unsigned long) stack + PAGE_SIZE - sizeof(void *);
    pid = fork();
    if(pid < 0)
    perror("fork");
    else if(pid == 0){
    child();
    }
    else {
    while(1){
    n = waitpid(pid, &status, WUNTRACED);
    if(n < 0){
    perror("waitpid");
    exit(1);
    }

    n = ptrace(PTRACE_GETREGS, pid, 0, regs);
    if(n < 0){
    perror("PTRACE_GETREGS");
    exit(1);
    }

    printf("Status 0x%x orig_eax 0x%x\n", status,
    regs[ORIG_EAX]);

    if(ptrace(PTRACE_SYSEMU, pid, 0, 0)){
    perror("PTRACE_SYSEMU");
    exit(1);
    }
    }
    }

    return 0;
    }
    -
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