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target-mips: Correct MIPS16/microMIPS branch size calculation

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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.

Backports commit c3577479815f5bcf9d38993967bca2115af245d8 from qemu
This commit is contained in:
Maciej W. Rozycki 2018-02-11 16:09:11 -05:00 committed by Lioncash
parent 283cbd0317
commit 4d9107be8a
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GPG key ID: 4E3C3CC1031BA9C7
2 changed files with 3 additions and 2 deletions
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3
qemu/target-mips/translate.c
View file

@ -19662,7 +19662,8 @@ 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;
}

2
qemu/translate-all.c
View file

@ -1579,7 +1579,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
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;
}