In the FPU emulator code of the MIPS, the Cause bits of the FCSR register
are not currently writeable by the ctc1 instruction. In odd corner cases,
this can cause problems. For example, a case existed where a divide-by-zero
exception was generated by the FPU, and the signal handler attempted to
restore the FPU registers to their state before the exception occurred. In
this particular setup, writing the old value to the FCSR register would
cause another divide-by-zero exception to occur immediately. The solution
is to change the ctc1 instruction emulator code to allow the Cause bits of
the FCSR register to be writeable. This is the behaviour of the hardware
that the code is emulating.
This problem was found by Shane McDonald, but the credit for the fix goes
to Kevin Kissell. In Kevin's words:
I submit that the bug is indeed in that ctc_op: case of the emulator. The
Cause bits (17:12) are supposed to be writable by that instruction, but the
CTC1 emulation won't let them be updated by the instruction. I think that
actually if you just completely removed lines 387-388 [...] things would
work a good deal better. At least, it would be a more accurate emulation of
the architecturally defined FPU. If I wanted to be really, really pedantic
(which I sometimes do), I'd also protect the reserved bits that aren't
necessarily writable.
Signed-off-by: Shane McDonald <mcdonald.shane@gmail.com>
To: anemo@mba.ocn.ne.jp
To: kevink@paralogos.com
To: sshtylyov@mvista.com
Patchwork: http://patchwork.linux-mips.org/patch/1205/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
---
On SMP systems, the collection of statistics can cause cache line
bouncing in the lines associated with the counters. Also there are
races incrementing the counters on multiple CPUs.
To fix both problems, we collect the statistics in per-CPU variables,
and add them up in the debugfs read operation.
As a test I ran the LTP float_bessel test on a 12 CPU Octeon system.
Without CONFIG_DEBUG_FS : 2602 seconds.
With CONFIG_DEBUG_FS: 2640 seconds.
With non-cpu-local atomic statistics: 14569 seconds.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Running a 64-bit kernel on a 64-bit CPU without an FPU would cause the
emulator to run in 32-bit mode. The c0_Status.FR bit is wired to zero
on systems without an FPU, so using that bit to decide how the emulator
behaves doesn't allow for proper emulation on 64-bit FPU-less
processors.
Instead, we need to select the emulator mode based on the user-space
ABI. Since the thread flag TIF_32BIT_REGS is used to set c0_Status.FR,
we can just use it to decide if the emulator should be in 32-bit or
64-bit mode.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Arguably using the address error handler has always been ugly. But with
processors that handle unaligned loads and stores in hardware the
current mechanism ceases to work so switch it to a BREAK instruction and
allocate break code 514 to the FPU emulator.
Yoichi Yuasa provided a build fix for CONFIG_BUG=n.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
debugfs_create_*() returns NULL on error. Make its caller debugfs_fpuemu
return -ENODEV on error.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Declaring emulpc and contpc as "unsigned long" can get rid of some casts.
This also get rid of some sparse warnings.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Export contents of struct mips_fpu_emulator_stats via debugfs.
There is no way to read these statistics for now but they (at least
the "emulated" count) might be sometimes useful for performance tuning
on FPU-less CPUs.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Make sure cpu_has_fpu (which uses smp_processor_id()) is used only in
atomic context.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
The struct mips_fpu_soft_struct and mips_fpu_hard_struct are
completely same now and the kernel fpu emulator assumes that. This
patch unifies them to mips_fpu_struct and get rid of mips_fpu_union.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
VA_TO_REG. Who ever wrote this apparently did enjoy the C Puzzle Book.
ISBN 0201604612, a little old but still fun reading for the next
blackout ;)
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This patch has fixed the following warnings.
arch/mips/kernel/genex.S:250:5: warning: "CONFIG_64BIT" is not defined
arch/mips/math-emu/cp1emu.c:1128:5: warning: "__mips64" is not defined
arch/mips/math-emu/cp1emu.c:1206:5: warning: "__mips64" is not defined
arch/mips/math-emu/cp1emu.c:1270:5: warning: "__mips64" is not defined
arch/mips/math-emu/cp1emu.c:323:5: warning: "__mips64" is not defined
arch/mips/math-emu/cp1emu.c:808:5: warning: "__mips64" is not defined
arch/mips/math-emu/cp1emu.c:953:5: warning: "__mips64" is not defined
arch/mips/mm/tlbex.c:519:5: warning: "CONFIG_64BIT" is not defined
include/asm/reg.h:73:5: warning: "CONFIG_64BIT" is not defined
Signed-off-by: Yoichi Yuasa <yuasa@hh.iij4u.or.jp>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
