Date: Thu, 18 Feb 2021 21:07:34 +0000 From: Jessica Clarke <jrtc27@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: John Baldwin <jhb@freebsd.org>, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 24fd63e0970f - main - mips: Don't set __NO_TLS to disable some uses of TLS. Message-ID: <DBFAB331-737A-44E0-BBAA-65AF2C870AA9@freebsd.org> In-Reply-To: <YC7TcMtrg8r7eAuL@kib.kiev.ua> References: <202102180035.11I0ZnL3070354@gitrepo.freebsd.org> <9687575c-dd7c-1496-850b-2018f4bca3da@FreeBSD.org> <YC7TcMtrg8r7eAuL@kib.kiev.ua>
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On 18 Feb 2021, at 20:52, Konstantin Belousov <kostikbel@gmail.com> = wrote: > On Wed, Feb 17, 2021 at 04:48:22PM -0800, John Baldwin wrote: >> On 2/17/21 4:35 PM, John Baldwin wrote: >>> The branch main has been updated by jhb: >>>=20 >>> URL: = https://cgit.FreeBSD.org/src/commit/?id=3D24fd63e0970f91189dd2acde987bd2e4= c8c04a50 >>>=20 >>> commit 24fd63e0970f91189dd2acde987bd2e4c8c04a50 >>> Author: John Baldwin <jhb@FreeBSD.org> >>> AuthorDate: 2021-02-18 00:34:23 +0000 >>> Commit: John Baldwin <jhb@FreeBSD.org> >>> CommitDate: 2021-02-18 00:34:23 +0000 >>>=20 >>> mips: Don't set __NO_TLS to disable some uses of TLS. >>> __NO_TLS was originally added to disable use of _Thread in the = locale >>> code in libc in 82dd5016bd749d1d9e1531bd1703aebeecceab34. At = the time >>> libc did not support TLS on MIPS (I believe), but TLS support = was >>> added to libc (at least _set_tp.c) for MIPS about a month after >>> __NO_TLS was added, but __NO_TLS was still left around. >>> Reviewed by: imp >>> Sponsored by: DARPA >>> Differential Revision: https://reviews.freebsd.org/D28713 >>> --- >>> sys/sys/cdefs.h | 3 +-- >>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>=20 >>> diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h >>> index 64f26480a2f5..ff18911f6acf 100644 >>> --- a/sys/sys/cdefs.h >>> +++ b/sys/sys/cdefs.h >>> @@ -768,8 +768,7 @@ >>> #endif >>> #endif /* __STDC_WANT_LIB_EXT1__ */ >>> -#if defined(__mips) || \ >>> - (defined(__powerpc64__) && (!defined(_CALL_ELF) || _CALL_ELF =3D=3D= 1)) >>> +#if defined(__powerpc64__) && (!defined(_CALL_ELF) || _CALL_ELF =3D=3D= 1) >>> #define __NO_TLS 1 >>> #endif >>=20 >> It would be really nice to kill __NO_TLS entirely. There is at least = one >> unconditional use of _Thread_local (sorry, should have used that = instead >> of _Thread above) in libc in stdlib/cxa_thread_atexit_impl.c, so it = seems >> highly unlikely that TLS is actually broken on any of our platforms = as the >> libc build would have been broken instead. >=20 > There is a difference between compile and runtime. The mentioned libc > use in cxa_thread_atexit_impl.c is to support some (I believe) rarely > used C++ feature of thread-local storage with destructors, so it might > be simply not observed often. OTOH, locale functions infect almost > everything string-related in libc, so the breakage would be quite > visible. It's also used in jemalloc for tsd_initialized which is a rather key variable, so if TLS is broken you won't get very far in userspace (source: I had to debug implementing it for CHERI-MIPS), well before you even think about getting to locale functions. > But, I wonder, what does CALL_ELF mean? Is it for old 64bit PowerPC = ABI, > that was abandoned with the switch to ELFv2? Yes, _CALL_ELF =3D=3D 2 for ELFv2. I highly doubt the defines were = needed for the ELFv1 ABI, but they're especially redundant now. Presumably David's original fixed commit[1] added powerpc64 to that list because TLS wasn't yet supported in LLVM; that happened later in 2012 and our wiki changed it to being implemented in December 2012[2]. So I suspect it should have been deleted 8 years ago. Jess [1] b0968176b3a821598a31de6698e01931d1417584 [2] = https://wiki.freebsd.org/action/diff/BuildingFreeBSDWithClang?action=3Ddif= f&rev1=3D340&rev2=3D341
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