On Fri, 11 Aug 2017, Mark Kettenis wrote:
> The diff below implements __cxa_thread_atexit(). Calls to this function
> are emitted by the compiler to schedule running desctructors for
> thread_local objects when a thread terminates or calls exit(3). The
> Linux implementation prevents unloading of shared libraries that
> registered such destructors to prevent things from crashing. This diff
> does not implement that functionality yet. I plan to add that later.
> I expect this to be a bit of a corner case.
>
> I've chosen to implement __cxa_thread_atexit() directly instead of
> __cxa_thread_atexit_impl(). I think that is cleaner. It means we
> don't need to make changes to libc++ for this to start working. It
> looks like modern libstdc++ version will detect __cxa_thread_atexit().
>
> This adds a member to the "TIB". Tis means that you'll need to
> install the new headers and rebuild ld.so before rebuilding libpthread
> and libc.
>
> This will require a libc minor bump. But maybe it could ride the
> scheduled major bump?
Either seems fine. Couple comments below...
> --- include/tib.h 20 Apr 2017 16:07:52 -0000 1.4
> +++ include/tib.h 11 Aug 2017 14:20:30 -0000
> @@ -135,6 +135,7 @@
> */
>
> struct tib {
> + void *tib_atexit;
> int tib_thread_flags; /* internal to libpthread */
> pid_t tib_tid;
> int tib_cantcancel;
> @@ -182,6 +183,7 @@ struct tib {
> int tib_cantcancel;
> pid_t tib_tid;
> int tib_thread_flags; /* internal to libpthread */
> + void *tib_atexit;
> #if !defined(__LP64__) && !defined(__i386)
> int __tib_padding; /* padding for 8byte alignment */
> #endif
To keep this structure a multiple of 8 in size, the padding conditionals
need to swap around, so that the extra member is only present on i386.
HOWEVER, looking again at _dl_tib_allocate(), I already taught it to round
up the sizes for correct alignment of the structs! I think __tib_padding
can go away now.
...
> +DEF_STRONG(__cxa_thread_atexit);
...
> +PROTO_NORMAL(__cxa_thread_atexit);
It's not actually called inside libc, right? If not, you can delete
DEF_STRONG() and use PROTO_STD_DEPRECATED() intead of PROTO_NORMAL() (case
IIb1 in libc/include/README)
Philip
