Date: Mon, 18 Jan 2016 12:49:48 -0800 From: John Baldwin <jhb@freebsd.org> To: Nathan Whitehorn <nwhitehorn@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r279189 - in head/sys/powerpc: aim fpu include powerpc Message-ID: <11668266.h2pHzfGYxF@ralph.baldwin.cx> In-Reply-To: <201502222140.t1MLeSFg075690@svn.freebsd.org> References: <201502222140.t1MLeSFg075690@svn.freebsd.org>
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On Sunday, February 22, 2015 09:40:28 PM Nathan Whitehorn wrote: > Author: nwhitehorn > Date: Sun Feb 22 21:40:27 2015 > New Revision: 279189 > URL: https://svnweb.freebsd.org/changeset/base/279189 > > Log: > Kernel support for the Vector-Scalar eXtension (VSX) found on the POWER7 > and POWER8. This instruction set unifies the 32 64-bit scalar floating > point registers with the 32 128-bit vector registers into a single bank > of 64 128-bit registers. Kernel support mostly amounts to saving and > restoring the wider version of the floating point registers and making > sure that both scalar FP and vector registers are enabled once a VSX > instruction is executed. get_mcontext() and friends currently cannot > see the high bits, which will require a little more work. > > As the system compiler (GCC 4.2) does not support VSX, making use of this > from userland requires either newer GCC or clang. > > Relnotes: yes > Sponsored by: FreeBSD Foundation > > Modified: > head/sys/powerpc/aim/trap.c > head/sys/powerpc/aim/trap_subr64.S > head/sys/powerpc/fpu/fpu_emu.c > head/sys/powerpc/fpu/fpu_explode.c > head/sys/powerpc/include/cpu.h > head/sys/powerpc/include/pcb.h > head/sys/powerpc/include/psl.h > head/sys/powerpc/include/reg.h > head/sys/powerpc/include/trap.h > head/sys/powerpc/powerpc/cpu.c > head/sys/powerpc/powerpc/db_trace.c > head/sys/powerpc/powerpc/exec_machdep.c > head/sys/powerpc/powerpc/fpu.c > > Modified: head/sys/powerpc/include/reg.h > ============================================================================== > --- head/sys/powerpc/include/reg.h Sun Feb 22 21:32:57 2015 (r279188) > +++ head/sys/powerpc/include/reg.h Sun Feb 22 21:40:27 2015 (r279189) > @@ -20,7 +20,10 @@ struct reg { > > /* Must match pcb.pcb_fpu */ > struct fpreg { > - double fpreg[32]; > + union { > + double fpr; > + uint64_t vsr[2]; > + } fpreg[32]; > double fpscr; > }; This breaks the ABI of struct fpreg which changes the format of coredumps. It also breaks the ABI of older versions of programs (such as debuggers) that use ptrace(PT_GETFPREGS) (the kernel will now overflow the user-allocated buffer if a debugger built on 10.x is run under an 11.0 kernel, and PT_SETFPREGS is going to also buffer overflow and store random garbage in the FP regs). Did you mean to alter the structure's layout? I can maybe fix upstream gdb to cope with either size, but it's a bit of a PITA. In particular, gdb assumes that all the floating point registers in struct fpreg are in a packed array (so it can use starting_offset + 8 * n to extract register 'n' and only the initial offset is something that different platform targets have to configure), so fixing this means having to add a lot of special cases and duplicate code that is otherwise shared across platforms. Hmm, I see that you preserved the ABI of mcontext by just copying the doubles. I think you should do the same for 'struct fpreg' restoring its ABI and we can use MD ptrace requests to fetch the VSX state. This is what Linux effectively does. -- John Baldwin
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