NetBSD Problem Report #58796

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Date: Thu, 31 Oct 2024 19:02:51 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: arm/mcontext.h has nested extern for _lwp_getprivate
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>Number:         58796
>Category:       misc
>Synopsis:       arm/mcontext.h has nested extern for _lwp_getprivate
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    misc-bug-people
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 31 19:05:00 +0000 2024
>Closed-Date:    Mon Mar 17 00:00:36 +0000 2025
>Last-Modified:  Mon Mar 17 00:00:36 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current, 10, 9, ...
>Organization:
The NestedexternLWP Private Foundation
>Environment:
>Description:
<lwp.h> (include/lwp.h) declares _lwp_getprivate, the out-of-line syscall stub in libc to query the lwp's private pointer.

<machine/mcontext.h> (sys/arch/*/include/mcontext.h) defines _lwp_getprivate_fast or _lwp_gettcb_fast and _lwp_settcb.  The Arm version is defined in terms of _lwp_getprivate as a fallback for some broken Arm cores.

Currently, all users of _lwp_getprivate/gettcb/settcb_fast are expected to (a) define _RTLD_SOURCE, _LIBC_SOURCE, or __LIBPTHREAD_SOURCE__, and (b) include <lwp.h>, which includes <machine/mcontext.h> via <sys/ucontext.h>, and which _then_ declares _lwp_getprivate.

So the declaration of _lwp_getprivate isn't available by the time Arm's <machine/mcontext.h> (sys/arch/arm/include/mcontext.h) needs it, and adding #include <lwp.h> to Arm's <machine/mcontext.h> would create a circular dependency with <lwp.h>.
>How-To-Repeat:
code inspection, and/or build with -Werror=nested-extern
>Fix:
1. Move the definitions of _lwp_getprivate/gettcb/settcb_fast (plus TLS_TP_OFFSET and TLS_DTV_OFFSET, and whatever other parts are directly relevant) to a new header file <machine/lwp_private.h>.

2. Use #include <lwp.h> in the Arm and PowerPC <machine/lwp_private.h> implementations (and whichever other ones need _lwp_getprivate/setprivate or similar).

3. Include <machine/lwp_private.h> explicitly in all users of _lwp_getprivate/gettcb/settcb_fast instead of using the kooky _RTLD_SOURCE/_LIBC_SOURCE/__LIBPTHREAD_SOURCE__ conditionalization.

>Release-Note:

>Audit-Trail:

State-Changed-From-To: open->closed
State-Changed-By: riastradh@NetBSD.org
State-Changed-When: Mon, 17 Mar 2025 00:00:36 +0000
State-Changed-Why:
fixed in HEAD, not worth pullup

https://mail-index.netbsd.org/source-changes/2024/11/30/msg154647.html



>Unformatted:

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