[Qemu-devel] [PATCH v3] target-arm: allow modifying vfp fpexc en bit only

[juha . riihimaki]

From: Juha Riihimäki <address@hidden>

All other bits except for the EN in the VFP FPEXC register are defined
as subarchitecture specific and real functionality for any of the
other bits has not been implemented in QEMU. However, current code
allows modifying all bits in the VFP FPEXC register leading to
problems when guest code is writing 1's to the subarchitecture
specific bits and checking whether the bits stay up to verify the
existence of functionality which in fact does not exist in QEMU.
This patch has been revised to include the same behavior change in
the gdb register write function.

Signed-off-by: Juha Riihimäki <address@hidden>
---
 target-arm/helper.c    |    2 +-
 target-arm/translate.c |    3 +++
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 701629a..ee5df59 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -233,7 +233,7 @@ static int vfp_gdb_set_reg(CPUState *env, uint8_t *buf, int 
reg)
     switch (reg - nregs) {
     case 0: env->vfp.xregs[ARM_VFP_FPSID] = ldl_p(buf); return 4;
     case 1: env->vfp.xregs[ARM_VFP_FPSCR] = ldl_p(buf); return 4;
-    case 2: env->vfp.xregs[ARM_VFP_FPEXC] = ldl_p(buf); return 4;
+    case 2: env->vfp.xregs[ARM_VFP_FPEXC] = ldl_p(buf) & (1 << 30); return 4;
     }
     return 0;
 }
diff --git a/target-arm/translate.c b/target-arm/translate.c
index 8503b92..d19ac7f 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -2804,6 +2804,9 @@ static int disas_vfp_insn(CPUState * env, DisasContext 
*s, uint32_t insn)
                         case ARM_VFP_FPEXC:
                             if (IS_USER(s))
                                 return 1;
+                            /* TODO: VFP subarchitecture support.
+                             * For now, keep the EN bit only */
+                            tcg_gen_andi_i32(tmp, tmp, 1 << 30);
                             store_cpu_field(tmp, vfp.xregs[rn]);
                             gen_lookup_tb(s);
                             break;
-- 
1.6.5