Re: CVS commit: src/doc

[David Holland <dholland-sourcechanges%netbsd.org@localhost>]

On Mon, Jan 02, 2017 at 05:18:49AM +0100, Kamil Rytarowski wrote:
 > > Historically exect() is used by debuggers to start debuggees. While
 > > it's equivalent to using PT_TRACE_ME followed by execve(), I think the
 > > result is that the new process first stops immediately after the exec
 > > finishes so that the debugger doesn't have to worry about stepping
 > > through the exec call in its own code.
 > > 
 > > This doesn't mean it shouldn't go away (or as much away as it can,
 > > that is, to COMPAT_70) but I'm not convinced there's no case for it.
 > > 
 > 
 > So, can I change exect(3) to something like:
 > 
 > int
 > exect(const char *path, char *const argv[], char *const envp[])
 > {
 >     if (ptrace(PT_TRACE_ME, 0, NULL, 0) == -1)
 >         return -1;
 >     return execve(path, argv, envp);
 > }
 > 
 > The current implementation of exect(3) (at least philosophically)
 > predates SIGTRAP on exec().

Not really; AFAIK, with that the target will first stop at the return
from the ptrace call, and also stop at the exec, whereas with
traditional exect it will first stop after the exec completes, in
__start or in ld.elf_so.

An unsophisticated debugger expecting the latter will almost certainly
be confused by the former.

Anyway, it needs to be kept in both the kernel and libc for compat so
there's not much to be gained by mucking with it. :-/

-- 
David A. Holland
dholland%netbsd.org@localhost