ptrace weirdness with 9.0-CURRENT

[Ali Polatel]

On Wed, 9 Feb 2011 01:55:42 +0200, Kostik Belousov <kostikbel at gmail.com> wrote:
> On Wed, Feb 09, 2011 at 01:49:52AM +0200, Kostik Belousov wrote:
> > On Wed, Feb 09, 2011 at 12:42:15AM +0200, Ali Polatel wrote:
> > > Hello everyone,
> > > 
> > > I'm the developer of pinktrace - http://dev.exherbo.org/~alip/pinktrace/
> > > - a simple ptrace() wrapper library for FreeBSD and Linux. I have set up
> > > a FreeBSD-9.0-CURRENT VM today to test various new features recently
> > > added to ptrace(). This is about a behaviour difference between
> > > 8.1-RELEASE and 9.0-CURRENT which I've noticed through a unit test of
> > > pinktrace. I don't want to bother you with the internals of this library
> > > so I'll briefly explain the problem.
> > > 
> > > I've inserted the testcase I've used below. The aim is to trace a
> > > open(NULL, 0) call which should fail with EFAULT. Running this on two
> > > different VMs I get:
> > > 
> > > % uname -a
> > > FreeBSD  9.0-CURRENT FreeBSD 9.0-CURRENT #0: Wed Feb  9 05:02:31 EET 2011     root@:/usr/obj/usr/src/sys/GENERIC  amd64
> > > % sudo cat /root/world.txt
> > > --------------------------------------------------------------
> > > >>> World build completed on Wed Feb  9 00:23:30 EET 2011
> > > --------------------------------------------------------------
> > > % gcc -Wall ptrace-amd64-fbsd-return.c
> > > % ./a.out
> > > retval:0 error:0
> > > 
> > > $ uname -a
> > > FreeBSD  8.1-RELEASE FreeBSD 8.1-RELEASE #0: Mon Jul 19 02:36:49 UTC 2010     root at mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
> > > $ gcc -Wall ptrace-amd64-fbsd-return.c
> > > $ ./a.out
> > > retval:14 error:1
> > > $ 
> > > 
> > > Important note: I couldn't notice a problem with truss tracing a
> > > open(NULL, 0) call so I think this is a problem with my testcase.
> > > I'll be happy if you can shed some light on what I'm doing wrong here:
> > There is no issue with ptrace(2). Your test fails because, apparently,
> > rtld in HEAD calls setjmp(3) when resolving symbols, and setjmp(3)
> > calls sigprocmask(2). The end result is that you get SCX event for
> > sigprocmask, and not for your open(2).

Ah interesting.

> > The issue with sigprocmask call from setjmp shall be fixed, but this
> > is not an issue with ptrace(2).
> 
> The following should fix the problem.

I confirm that this patch fixes the problem, thanks!
 
> diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
> index 50ab393..948cf49 100644
> --- a/libexec/rtld-elf/rtld.c
> +++ b/libexec/rtld-elf/rtld.c
> @@ -560,7 +560,7 @@ _rtld_bind(Obj_Entry *obj, Elf_Size reloff)
>      RtldLockState lockstate;
>  
>      rlock_acquire(rtld_bind_lock, &lockstate);
> -    if (setjmp(lockstate.env) != 0)
> +    if (sigsetjmp(lockstate.env, 0) != 0)
>  	    lock_upgrade(rtld_bind_lock, &lockstate);
>      if (obj->pltrel)
>  	rel = (const Elf_Rel *) ((caddr_t) obj->pltrel + reloff);
> @@ -2142,7 +2142,7 @@ dlopen(const char *name, int mode)
>      ld_tracing = (mode & RTLD_TRACE) == 0 ? NULL : "1";
>      if (ld_tracing != NULL) {
>  	rlock_acquire(rtld_bind_lock, &lockstate);
> -	if (setjmp(lockstate.env) != 0)
> +	if (sigsetjmp(lockstate.env, 0) != 0)
>  	    lock_upgrade(rtld_bind_lock, &lockstate);
>  	environ = (char **)*get_program_var_addr("environ", &lockstate);
>  	lock_release(rtld_bind_lock, &lockstate);
> @@ -2264,7 +2264,7 @@ do_dlsym(void *handle, const char *name, void *retaddr, const Ver_Entry *ve,
>      req.lockstate = &lockstate;
>  
>      rlock_acquire(rtld_bind_lock, &lockstate);
> -    if (setjmp(lockstate.env) != 0)
> +    if (sigsetjmp(lockstate.env, 0) != 0)
>  	    lock_upgrade(rtld_bind_lock, &lockstate);
>      if (handle == NULL || handle == RTLD_NEXT ||
>  	handle == RTLD_DEFAULT || handle == RTLD_SELF) {
> diff --git a/libexec/rtld-elf/rtld.h b/libexec/rtld-elf/rtld.h
> index 8941d29..bb365a7 100644
> --- a/libexec/rtld-elf/rtld.h
> +++ b/libexec/rtld-elf/rtld.h
> @@ -276,7 +276,7 @@ typedef struct Struct_DoneList {
>  
>  struct Struct_RtldLockState {
>  	int lockstate;
> -	jmp_buf env;
> +	sigjmp_buf env;
>  };
>  
>  /*
> diff --git a/libexec/rtld-elf/rtld_lock.c b/libexec/rtld-elf/rtld_lock.c
> index e76a4da..024e1e2 100644
> --- a/libexec/rtld-elf/rtld_lock.c
> +++ b/libexec/rtld-elf/rtld_lock.c
> @@ -259,7 +259,7 @@ lock_restart_for_upgrade(RtldLockState *lockstate)
>  	case RTLD_LOCK_WLOCKED:
>  		break;
>  	case RTLD_LOCK_RLOCKED:
> -		longjmp(lockstate->env, 1);
> +		siglongjmp(lockstate->env, 1);
>  		break;
>  	default:
>  		assert(0);

-- 
Regards,
Ali Polatel
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