* Jann Horn:
> ptrace() with requests PTRACE_PEEKTEXT, PTRACE_PEEKDATA and
> PTRACE_PEEKUSER can set errno to zero. AFAICS this is for a good reason (so
> that you can tell the difference between a successful PEEK with a result of
> -1 and a failed PEEK, even if you forget to clear errno yourself), but it
> technically violates the rules described in the errno.3 manpage.
>
> glibc snippet from sysdeps/unix/sysv/linux/ptrace.c:
>
> res = INLINE_SYSCALL (ptrace, 4, request, pid, addr, data);
> if (res >= 0 && request > 0 && request < 4)
> {
> __set_errno (0);
> return ret;
> }
glibc has various special cases like this for interfaces where the
return value is ambiguous, such as NULL from NSS functions:
<https://sourceware.org/bugzilla/show_bug.cgi?id=3195#c1>
I'm a bit reluctant to fix this due to the backwards compatibility
impact.
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