Date: Thu, 09 Feb 2012 14:41:08 -0800 From: Oleksandr Tymoshenko <gonzo@freebsd.org> To: Robert Millan <rmh@debian.org> Cc: freebsd-mips@freebsd.org Subject: Re: [PATCH] Retrieval of TLS pointer via RDHWR Message-ID: <4F344B84.4040107@freebsd.org> In-Reply-To: <AANLkTimg3CUk0p8YPyepiumEHvKo2F6jdVA0=1CefYrQ@mail.gmail.com> References: <AANLkTimg3CUk0p8YPyepiumEHvKo2F6jdVA0=1CefYrQ@mail.gmail.com>
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On 08/12/2010 8:34 AM, Robert Millan wrote: > This patch implements support for retrieving the TLS pointer via RDHWR > instruction. > > It is implemented through emulation for platforms that don't provide > this instruction natively (such as gxemul/malta). Platforms that do > provide it would need a separate patch. > > Reading register $29 with RDHWR is becoming the de-facto standard to > implement TLS. According to linux-mips wiki, MIPS Technologies has > reserved hardware register $29 for ABI use. Furthermore current GCC [1] > makes the following assumptions: > - RDHWR is natively available or otherwise emulated by the kernel > - Register $29 holds the TLS pointer > > [1] gcc-4.4.4/gcc/config/mips/mips.md reads: > > ;; The TLS base pointer is accessed via "rdhwr $3, $29". No current > ;; MIPS architecture defines this register, and no current > ;; implementation provides it; instead, any OS which supports TLS is > ;; expected to trap and emulate this instruction. rdhwr is part of the > ;; MIPS 32r2 specification, but we use it on any architecture because > ;; we expect it to be emulated. Hi Robert, It's a shame that it took a year to commit this patch :( but finally it made it to SVN. I modified it a little bit to be more universal and MIPS64-compatible.
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