[Qemu-devel] [PATCH v2 1/2] linux-user: Fix MIPS ISA transitions during signal handling

[Kwok Cheung Yeung <kcy@codesourcery.com>]

Processors supporting the MIPS16 or microMIPS ISAs set bit 0 in target
addresses to indicate that the target is written using a compressed ISA.

During signal handling, when jumping to or returning from a signal
handler, bit 0 of the destination PC is inspected and MIPS_HFLAG_M16 in
hflags cleared or set accordingly.  Bit 0 of the PC is then cleared.

Signed-off-by: Kwok Cheung Yeung <kcy@codesourcery.com>
---
 linux-user/signal.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 1055507..dc34ae7 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -2620,6 +2620,15 @@ get_sigframe(struct target_sigaction *ka, CPUMIPSState *regs, size_t frame_size)
     return (sp - frame_size) & ~7;
 }
 
+static void mips_set_hflags_isa_mode_from_pc(CPUMIPSState *env)
+{
+    if (env->insn_flags & (ASE_MIPS16 | ASE_MICROMIPS)) {
+        env->hflags &= ~MIPS_HFLAG_M16;
+        env->hflags |= (env->active_tc.PC & 1) << MIPS_HFLAG_M16_SHIFT;
+        env->active_tc.PC &= ~(target_ulong) 1;
+    }
+}
+
 # if defined(TARGET_ABI_MIPSO32)
 /* compare linux/arch/mips/kernel/signal.c:setup_frame() */
 static void setup_frame(int sig, struct target_sigaction * ka,
@@ -2662,6 +2671,7 @@ static void setup_frame(int sig, struct target_sigaction * ka,
     * since it returns to userland using eret
     * we cannot do this here, and we must set PC directly */
     regs->active_tc.PC = regs->active_tc.gpr[25] = ka->_sa_handler;
+    mips_set_hflags_isa_mode_from_pc(regs);
     unlock_user_struct(frame, frame_addr, 1);
     return;
 
@@ -2709,6 +2719,7 @@ long do_sigreturn(CPUMIPSState *regs)
 #endif
 
     regs->active_tc.PC = regs->CP0_EPC;
+    mips_set_hflags_isa_mode_from_pc(regs);
     /* I am not sure this is right, but it seems to work
     * maybe a problem with nested signals ? */
     regs->CP0_EPC = 0;
@@ -2771,6 +2782,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,
     * since it returns to userland using eret
     * we cannot do this here, and we must set PC directly */
     env->active_tc.PC = env->active_tc.gpr[25] = ka->_sa_handler;
+    mips_set_hflags_isa_mode_from_pc(env);
     unlock_user_struct(frame, frame_addr, 1);
     return;
 
@@ -2804,6 +2816,7 @@ long do_rt_sigreturn(CPUMIPSState *env)
         goto badframe;
 
     env->active_tc.PC = env->CP0_EPC;
+    mips_set_hflags_isa_mode_from_pc(env);
     /* I am not sure this is right, but it seems to work
     * maybe a problem with nested signals ? */
     env->CP0_EPC = 0;
-- 
1.8.1.2