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[Qemu-devel] [PULL 40/40] target-ppc: mcrfs should always update FEX/VX
From: |
David Gibson |
Subject: |
[Qemu-devel] [PULL 40/40] target-ppc: mcrfs should always update FEX/VX and only clear exception bits |
Date: |
Mon, 1 Feb 2016 13:31:08 +1100 |
From: James Clarke <address@hidden>
Here is the description of the mcrfs instruction from the PowerPC Architecture
Book, Version 2.02, Book I: PowerPC User Instruction Set Architecture
(http://www.ibm.com/developerworks/systems/library/es-archguide-v2.html), found
on page 120:
The contents of FPSCR field BFA are copied to Condition Register field BF.
All exception bits copied are set to 0 in the FPSCR. If the FX bit is
copied, it is set to 0 in the FPSCR.
Special Registers Altered:
CR field BF
FX OX (if BFA=0)
UX ZX XX VXSNAN (if BFA=1)
VXISI VXIDI VXZDZ VXIMZ (if BFA=2)
VXVC (if BFA=3)
VXSOFT VXSQRT VXCVI (if BFA=5)
However, currently every bit in FPSCR field BFA is set to 0, including ones not
on that list.
This can be seen in the following simple C program:
#include <fenv.h>
#include <stdio.h>
int main(int argc, char **argv) {
int ret;
ret = fegetround();
printf("Current rounding: %d\n", ret);
ret = fesetround(FE_UPWARD);
printf("Setting to FE_UPWARD (%d): %d\n", FE_UPWARD, ret);
ret = fegetround();
printf("Current rounding: %d\n", ret);
ret = fegetround();
printf("Current rounding: %d\n", ret);
return 0;
}
which gave the output (before this commit):
Current rounding: 0
Setting to FE_UPWARD (2): 0
Current rounding: 2
Current rounding: 0
instead of (after this commit):
Current rounding: 0
Setting to FE_UPWARD (2): 0
Current rounding: 2
Current rounding: 2
The relevant disassembly is in fegetround(), which, on my system, is:
__GI___fegetround:
<+0>: mcrfs cr7, cr7
<+4>: mfcr r3
<+8>: clrldi r3, r3, 62
<+12>: blr
What happens is that, the first time fegetround() is called, FPSCR field 7 is
retrieved. However, because of the bug in mcrfs, the entirety of field 7 is set
to 0, which includes the rounding mode.
There are other issues this will fix, such as condition flags not persisting
when they should if read, and if you were to read a specific field with some
exception bits set, but no others were set in the entire register, then the
bits would be cleared correctly, but FEX/VX would not be updated to 0 as they
should be.
Signed-off-by: James Clarke <address@hidden>
Signed-off-by: David Gibson <address@hidden>
---
target-ppc/cpu.h | 6 ++++++
target-ppc/translate.c | 21 +++++++++++++++++----
2 files changed, 23 insertions(+), 4 deletions(-)
diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
index f300c86..892f4dc 100644
--- a/target-ppc/cpu.h
+++ b/target-ppc/cpu.h
@@ -719,6 +719,12 @@ enum {
#define FP_RN1 (1ull << FPSCR_RN1)
#define FP_RN (1ull << FPSCR_RN)
+/* the exception bits which can be cleared by mcrfs - includes FX */
+#define FP_EX_CLEAR_BITS (FP_FX | FP_OX | FP_UX | FP_ZX | \
+ FP_XX | FP_VXSNAN | FP_VXISI | FP_VXIDI | \
+ FP_VXZDZ | FP_VXIMZ | FP_VXVC | FP_VXSOFT | \
+ FP_VXSQRT | FP_VXCVI)
+
/*****************************************************************************/
/* Vector status and control register */
#define VSCR_NJ 16 /* Vector non-java */
diff --git a/target-ppc/translate.c b/target-ppc/translate.c
index 0219d38..7db3145 100644
--- a/target-ppc/translate.c
+++ b/target-ppc/translate.c
@@ -2501,18 +2501,31 @@ static void gen_fmrgow(DisasContext *ctx)
static void gen_mcrfs(DisasContext *ctx)
{
TCGv tmp = tcg_temp_new();
+ TCGv_i32 tmask;
+ TCGv_i64 tnew_fpscr = tcg_temp_new_i64();
int bfa;
+ int nibble;
+ int shift;
if (unlikely(!ctx->fpu_enabled)) {
gen_exception(ctx, POWERPC_EXCP_FPU);
return;
}
- bfa = 4 * (7 - crfS(ctx->opcode));
- tcg_gen_shri_tl(tmp, cpu_fpscr, bfa);
+ bfa = crfS(ctx->opcode);
+ nibble = 7 - bfa;
+ shift = 4 * nibble;
+ tcg_gen_shri_tl(tmp, cpu_fpscr, shift);
tcg_gen_trunc_tl_i32(cpu_crf[crfD(ctx->opcode)], tmp);
- tcg_temp_free(tmp);
tcg_gen_andi_i32(cpu_crf[crfD(ctx->opcode)], cpu_crf[crfD(ctx->opcode)],
0xf);
- tcg_gen_andi_tl(cpu_fpscr, cpu_fpscr, ~(0xF << bfa));
+ tcg_temp_free(tmp);
+ tcg_gen_extu_tl_i64(tnew_fpscr, cpu_fpscr);
+ /* Only the exception bits (including FX) should be cleared if read */
+ tcg_gen_andi_i64(tnew_fpscr, tnew_fpscr, ~((0xF << shift) &
FP_EX_CLEAR_BITS));
+ /* FEX and VX need to be updated, so don't set fpscr directly */
+ tmask = tcg_const_i32(1 << nibble);
+ gen_helper_store_fpscr(cpu_env, tnew_fpscr, tmask);
+ tcg_temp_free_i32(tmask);
+ tcg_temp_free_i64(tnew_fpscr);
}
/* mffs */
--
2.5.0
- [Qemu-devel] [PULL 00/40] ppc-for-2.6 queue 20160201, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 04/40] macio: add dma_active to VMStateDescription, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 01/40] target-ppc: Use sensible POWER8/POWER8E versions, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 02/40] target-ppc: use cpu_write_xer() helper in cpu_post_load, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 14/40] pseries: Clean up error handling in spapr_vga_init(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 12/40] pseries: Clean up error handling of spapr_cpu_init(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 11/40] ppc: Clean up error handling in ppc_set_compat(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 40/40] target-ppc: mcrfs should always update FEX/VX and only clear exception bits,
David Gibson <=
- [Qemu-devel] [PULL 16/40] pseries: Clean up error handling in xics_system_init(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 21/40] target-ppc: gdbstub: fix float registers for little-endian guests, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 08/40] spapr: Remove rtas_st_buffer_direct(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 07/40] spapr: Small fixes to rtas_ibm_get_system_parameter, remove rtas_st_buffer, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 20/40] target-ppc: rename and export maybe_bswap_register(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 13/40] pseries: Clean up error handling in spapr_validate_node_memory(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 22/40] target-ppc: gdbstub: introduce avr_need_swap(), David Gibson, 2016/01/31
- [Qemu-devel] [PULL 23/40] target-ppc: gdbstub: fix altivec registers for little-endian guests, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 28/40] uninorth.c: add support for UniNorth kMacRISCPCIAddressSelect (0x48) register, David Gibson, 2016/01/31
- [Qemu-devel] [PULL 29/40] target-ppc: Remove unused kvmppc_read_segment_page_sizes() stub, David Gibson, 2016/01/31