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ptrace: Stop a traced thread when it exists from execve

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This was a missing feature in the PT_TRACEME command.

This feature allows the tracer to interact with the tracee before the
tracee has started executing its program.

It will be useful for automatically inserting a breakpoint at a
debugged program's entry point.
This commit is contained in:
Itamar 2020-04-06 16:08:25 +03:00 • committed by Andreas Kling
parent 4568a628f9
commit 0431712660
3 changed files with 58 additions and 16 deletions
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57
Applications/Debugger/main.cpp
View file

@ -90,19 +90,42 @@ void run_child_and_attach(char** argv)
exit(1);
}
dbg() << "debugee should continue until before execve exit";
if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
perror("continue");
}
// we want to continue until the exit from the 'execve' sycsall
// we do this to ensure that when we start debugging the process,
// it executes the target image, and not the forked image of the debugger
// NOTE: we only need to do this when we are debugging a new process (i.e not attaching to a process that's already running!)
if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
perror("syscall");
exit(1);
}
// if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
// perror("syscall");
// exit(1);
// }
if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
perror("wait_pid");
exit(1);
}
// dbg() << "debugee should continue until after execve exit";
// sleep(3);
// if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
// perror("continue");
// }
// sleep(10);
// if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
// perror("wait_pid");
// exit(1);
// }
// dbg() << "debugee should already be running";
// if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
// perror("continue");
// }
}
VirtualAddress get_entry_point(int pid)
@ -138,9 +161,23 @@ int main(int argc, char** argv)
auto entry_point = get_entry_point(g_pid);
dbg() << "entry point:" << entry_point;
uint32_t data = ptrace(PT_PEEK, g_pid, (void*)entry_point.as_ptr(), 0);
// u8* as_bytes = reinterpret_cast<u8*>(&data);
// as_bytes[0] = 0xcc;
dbg() << "peeked data:" << (void*)data;
data = (data & ~(uint32_t)0xff) | 0xcc;
data = 0xccccccc;
if (ptrace(PT_POKE, g_pid, (void*)entry_point.as_ptr(), data) < 0) {
perror("poke");
return 1;
}
dbg() << "continuting";
if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
perror("continue");
}
dbg() << "continued";
// wait for breakpoint
if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
@ -156,20 +193,14 @@ int main(int argc, char** argv)
return 1;
}
printf("eip:0x%x\n", regs.eip);
uint32_t data = ptrace(PT_PEEK, g_pid, (void*)regs.eip, 0);
printf("peeked data: 0x%x\n", data);
if (ptrace(PT_POKE, g_pid, (void*)regs.eip, data) < 0) {
perror("poke");
return 1;
}
dbg() << "eip after breakpoint: " << (void*)regs.eip;
if (ptrace(PT_CONTINUE, g_pid, 0, 0) == -1) {
perror("continue");
}
// wait for end
if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
perror("waitpid");
return 1;