On Sat, Feb 13, 2016 at 09:10:30PM -0800, Philip Guenther wrote:
> On Sat, Feb 13, 2016 at 12:31 PM, Michal Mazurek wrote:
> > When compiling a program that calls pledge(2) with "-pg" the resulting
> > binary will execute seemingly fine, but at the very end die with:
> > Abort trap (core dumped)
> > I think the problem lies in a call to profil(2).
> >
> > Is this a bug or a feature?
>
> Seems like a bug. _mcleanup() is invoked via the atexit() in gcrt0.o
> (c.f. lib/csu/crt0.c)
I would said "feature" instead of bug :)
In fact, I don't think a pledged program should not be profiled...
Profiling is for developpment code, and pledge is more for
production-code.
If profiling is needed, pledge(2) should be disabled:
1. by commenting the pledge(2) call
2. by adding `#define pledge(pr,pa) 0' after unistd.h include
3. by passing -D'pledge(pr,pa)=_nopledge' as compiler option (but I
am unsure if it makes a use of uninitialized variable or if compiler
initialize it to 0 alone).
Eventually is it acceptable to provide an unistd.h that mask pledge(2)
(and issue a #warning) when compiling with -pg ?
> Fixing things so this works will require at least two things:
> 1) pledge will need to always permit profil(NULL,0,0,0) for the
> moncontrol(0) performed by _mcleanup()
> 2) pledge will need to permit opening and writing to "gmon.out"
> (ignore the $PROFDIR stuff) if and only if profil() had been used.
>
> (The fallback code to use setitimer() if sysctl() fails seems
> pointless: when would that fail and setitimer() succeed?)
For a having a profiled program pledged it would need parts of:
- "stdio" : issetugid(), getpid(), write(), close(), munmap()
- "cpath" : open(O_CREAT)
and profil(2)
It is doable if we require at least "stdio" for profiling to work. else
it is too intrusive (require all previous syscall to be declared
PLEDGE_ALWAYS in `pledge_syscalls' array, and having a `pledge_profil'
call in each of them).
Additionnally, the fact to ignore $PROFDIR stuff would be more complex:
userland has no way to know the running program is pledged or not.
--
Sebastien Marie
