runtime: add the ability to set exterrors in userspace

[brooks]

Summary

The UEXTERROR(3) macro is a partial analog to EXTERROR(9) that sets
the current user exterror state and errno. The main difference is
that it returns no value and sets errno directly since that's the
typical pattern in libraries.

Effort: CHERI upstreaming
Sponsored by: Innovate UK

[brooks]

The big thing that needs to be dealt with for this to make sense is to have a way to specify the filename that isn't a table embedded in libc. A first cut could be a special index that means no-file and perhaps using -1 as the line, but without that, we can't scale beyond files in the base system. (This also poses a problem for out of tree kernel modules.) We might also want macros like the kernel, but I'm less sure of that.

[kib]

lib/libthr/thread/thr_syscalls.c

664

Create a libc helper in the private version namespace that takes uexterrp, and call it there and in the libc' uexterr_set().

[brooks]

Add helper in libc. Tag categories as user space.

[kib]

lib/libc/gen/uexterr_gettext.c

39

Stylistically, I do not see a need in this blank line, and in the blank line at 60.

[brooks]

Add UEXTERROR() analog to EXTERROR(). It differs in that it just wraps uexterr_set and thus it gets a different name.

[brooks]

Add docs. Make uexterr_set return void.

[kib]

include/uexterror.h

9

I believe you need to add your copyright there and in other sources.

lib/libc/gen/uexterr_gettext.c

28

I think these functions should go into separate source file in libc. There is no reason to bring uexterror_set() into the static binary if only gettext() is used.

[brooks]

Move to its own file, document, update copyrights

[brooks]

include/uexterror.h

9

Indeed, can we drop the All rights reserved.? The project doesn't want that in new copyrights.

[kib]

include/uexterror.h

9

Perhaps. Ask Ed, I used the header mandated by my contract.

lib/libc/gen/uexterr_gettext.c

13–14

To be perfect, this structure should go into a dedicated .c/.o as well.

[brooks]

Move global struct uexterror and constructor to its own file

[brooks]

include/uexterror.h

9

Tagging @emaste

[kib]

lib/libc/gen/uexterror.3

130

Definitely not 15.0

[brooks]

Correct feature introduction to 16.0. Bump doc date.