On Fri, 2013-06-07 at 07:45 +0000, Zang Roy-R61911 wrote:
>
> > -----Original Message-----
> > From: Benjamin Herrenschmidt [mailto:b...@kernel.crashing.org]
> > Another question...
> >
> > Do you guys happen to have a patch to emulate fsqrt in the kernel ?
> >
> > Fedora 19 seems to be using it ... among others.
> You mean this one
> arch/powerpc/math-emu/fsqrt.c ?
No. This is for setups that have no FPU, I don't think that will work
with an actual FPU.
fsqrt is an optional instruction in the architecture and FSL chips don't
use it. However it looks like Fedora is compiled with a toolchain that
generates it.
I've successfully launched the Fedora installer using this hack in the
kernel:
>From f75adba1ee91691d431e283184e15412114000d1 Mon Sep 17 00:00:00 2001
From: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Date: Fri, 7 Jun 2013 18:42:44 +1000
Subject: [PATCH] Gross hack
---
arch/powerpc/include/asm/ppc-opcode.h | 2 ++
arch/powerpc/kernel/Makefile | 4 ++-
arch/powerpc/kernel/fsqrt-emu.c | 44 +++++++++++++++++++++++++++++++++
arch/powerpc/kernel/traps.c | 7 ++++++
4 files changed, 56 insertions(+), 1 deletion(-)
create mode 100644 arch/powerpc/kernel/fsqrt-emu.c
diff --git a/arch/powerpc/include/asm/ppc-opcode.h
b/arch/powerpc/include/asm/ppc-opcode.h
index eccfc16..146c5e9 100644
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h
@@ -88,6 +88,8 @@
#define PPC_INST_DCBA_MASK 0xfc0007fe
#define PPC_INST_DCBAL 0x7c2005ec
#define PPC_INST_DCBZL 0x7c2007ec
+#define PPC_INST_FSQRT 0xfc00002c
+#define PPC_INST_FSQRT_MASK 0xfc1f07fe
#define PPC_INST_ICBT 0x7c00002c
#define PPC_INST_ISEL 0x7c00001e
#define PPC_INST_ISEL_MASK 0xfc00003e
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index f960a79..64c9962 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -26,6 +26,8 @@ CFLAGS_REMOVE_ftrace.o = -pg -mno-sched-epilog
CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
endif
+CFLAGS_REMOVE_fsqrt-emu.o = -msoft-float
+
obj-y := cputable.o ptrace.o syscalls.o \
irq.o align.o signal_32.o pmc.o vdso.o \
process.o systbl.o idle.o \
@@ -34,7 +36,7 @@ obj-y := cputable.o ptrace.o
syscalls.o \
udbg.o misc.o io.o dma.o \
misc_$(CONFIG_WORD_SIZE).o vdso32/
obj-$(CONFIG_PPC64) += setup_64.o sys_ppc32.o \
- signal_64.o ptrace32.o \
+ signal_64.o ptrace32.o fsqrt-emu.o \
paca.o nvram_64.o firmware.o
obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_ppc970.o cpu_setup_pa6t.o
diff --git a/arch/powerpc/kernel/fsqrt-emu.c b/arch/powerpc/kernel/fsqrt-emu.c
new file mode 100644
index 0000000..2da4f71
--- /dev/null
+++ b/arch/powerpc/kernel/fsqrt-emu.c
@@ -0,0 +1,44 @@
+#include <linux/kernel.h>
+#include <linux/preempt.h>
+#include <linux/sched.h>
+#include <asm/ptrace.h>
+#include <asm/processor.h>
+#include <asm/switch_to.h>
+
+static double crackpot_sqrt(double val)
+{
+ int i;
+ float x, y;
+ const float f = 1.5F;
+
+ x = val * 0.5F;
+ y = val;
+ i = * ( int * ) &y;
+ i = 0x5f3759df - ( i >> 1 );
+ y = * ( float * ) &i;
+ y = y * ( f - ( x * y * y ) );
+ y = y * ( f - ( x * y * y ) );
+ return val * y;
+}
+
+int emulate_fsqrt_inst(struct pt_regs *regs, u32 instword)
+{
+ unsigned int frt_r = (instword >> 21) & 0x1f;
+ unsigned int frb_r = (instword >> 21) & 0x1f;
+ double frt, frb;
+
+ /* XXX THIS WHOLE THING IS JUST A HACK ! */
+ preempt_disable();
+ enable_kernel_fp();
+ frb = current->thread.fpr[frb_r][0];
+ frt = crackpot_sqrt(frb);
+ current->thread.fpr[frt_r][0] = frt;
+ if (instword & 1)
+ regs->ccr &= 0xff00ffff;
+ preempt_enable();
+
+ return 0;
+}
+
+
+
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 6dfbb38..e677792 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -938,6 +938,8 @@ static int emulate_isel(struct pt_regs *regs, u32 instword)
return 0;
}
+extern int emulate_fsqrt_inst(struct pt_regs *regs, u32 instword);
+
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
static inline bool tm_abort_check(struct pt_regs *regs, int cause)
{
@@ -1018,6 +1020,11 @@ static int emulate_instruction(struct pt_regs *regs)
return emulate_isel(regs, instword);
}
+ if ((instword & PPC_INST_FSQRT_MASK) == PPC_INST_FSQRT) {
+ PPC_WARN_EMULATED(isel, regs);
+ return emulate_fsqrt_inst(regs, instword);
+ }
+
#ifdef CONFIG_PPC64
/* Emulate the mfspr rD, DSCR. */
if ((((instword & PPC_INST_MFSPR_DSCR_USER_MASK) ==
--
1.7.10.4
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