[Qemu-devel] [PATCH v2] mips: Correct MIPS16/microMIPS branch size calculation

[Maciej W. Rozycki]

Correct MIPS16/microMIPS branch size calculation in PC adjustment 
needed:

- to set the value of CP0.ErrorEPC at the entry to the reset exception,

- for the purpose of branch reexecution in the context of device I/O.

Follow the approach taken in `exception_resume_pc' for ordinary, Debug 
and NMI exceptions.

MIPS16 and microMIPS branches can be 2 or 4 bytes in size and that has 
to be reflected in calculation.  Original MIPS ISA branches, which is 
where this code originates from, are always 4 bytes long, just as all 
original MIPS ISA instructions.

Signed-off-by: Nathan Froyd <address@hidden>
Signed-off-by: Maciej W. Rozycki <address@hidden>
---
 Another change that has waited for too long, with the original 
discussion archived here:

http://lists.nongnu.org/archive/html/qemu-devel/2012-06/msg01230.html

Resending with what hopefully is a better description and updated to 
reflect the move of `cpu_io_recompile' from exec.c to translate-all.c.

 Please apply,

  Maciej

qemu-mips-b16.diff
Index: qemu-git-trunk/target-mips/translate.c
===================================================================
--- qemu-git-trunk.orig/target-mips/translate.c 2014-11-07 18:34:30.927788566 
+0000
+++ qemu-git-trunk/target-mips/translate.c      2014-11-07 18:34:35.428958223 
+0000
@@ -19452,7 +19452,8 @@ void cpu_state_reset(CPUMIPSState *env)
     if (env->hflags & MIPS_HFLAG_BMASK) {
         /* If the exception was raised from a delay slot,
            come back to the jump.  */
-        env->CP0_ErrorEPC = env->active_tc.PC - 4;
+        env->CP0_ErrorEPC = (env->active_tc.PC
+                             - (env->hflags & MIPS_HFLAG_B16 ? 2 : 4));
     } else {
         env->CP0_ErrorEPC = env->active_tc.PC;
     }
Index: qemu-git-trunk/translate-all.c
===================================================================
--- qemu-git-trunk.orig/translate-all.c 2014-11-07 17:33:13.037575065 +0000
+++ qemu-git-trunk/translate-all.c      2014-11-07 18:34:35.428958223 +0000
@@ -1534,7 +1534,7 @@ void cpu_io_recompile(CPUState *cpu, uin
        branch.  */
 #if defined(TARGET_MIPS)
     if ((env->hflags & MIPS_HFLAG_BMASK) != 0 && n > 1) {
-        env->active_tc.PC -= 4;
+        env->active_tc.PC -= (env->hflags & MIPS_HFLAG_B16 ? 2 : 4);
         cpu->icount_decr.u16.low++;
         env->hflags &= ~MIPS_HFLAG_BMASK;
     }