Re: PATCH: don't call cleanup handlers after a regular return from the thread start function

[Rich Felker <dalias@libc.org>]

On Tue, Aug 05, 2014 at 06:51:34PM +0200, Jens Gustedt wrote:
> Don't call cleanup handlers after a regular return from the thread
> start function
> 
> The chained list of cleanup handler function uses list items that are
> local to the respective function of a cleanup block. In case of a
> return out of the middle of a cleanup block, using these list items
> can lead to UB.
> 
> POSIX lists three different cases in which a cleanup handler that is
> established on the cleanup stack has to be executed. Regular return
> from the thread start function is not among these cases.
> 
> Linux manpages are more explicit and state:
> 
>     Clean-up handlers are not called if the thread terminates by
>     performing a return from the thread start function.
> 
> This patch aligns musl to that behavior.

Could you clarify why this patch is necessary? I think such a return
is explicitly UB:

"The effect of the use of return, break, continue, and goto to
prematurely leave a code block described by a pair of
pthread_cleanup_push() and pthread_cleanup_pop() functions calls is
undefined."

http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_cleanup_pop.html

I don't see why the thread start function should be treated as special
here.

Rich