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target-mips: fix hflags modified in delay / forbidden slot 

All instructions which may change hflags terminate tb. However, this doesn't
work if such an instruction is placed in delay or forbidden slot.
gen_branch() clears MIPS_HFLAG_BMASK in ctx->hflags and then generates code
to overwrite hflags with ctx->hflags, consequently we loose any execution-time
hflags modifications. For example, in the following scenario hflag related to
Status.CU1 will not be updated:
    /* Set Status.CU1 in delay slot */
    mfc0  $24, $12, 0
    lui   $25, 0x2000
    or    $25, $25, $24
    b     check_Status_CU1
    mtc0  $25, $12, 0

With this change we clear MIPS_HFLAG_BMASK in execution-time hflags if
instruction in delay or forbidden slot wants to terminate tb for some reason
(i.e. ctx->bstate != BS_NONE).

Also, die early and loudly if "unknown branch" is encountered as this should
never happen.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
This commit is contained in:
Leon Alrae 2015-01-29 16:15:00 +00:00
parent 62c688693b
commit a5f533909e
1 changed files with 15 additions and 4 deletions
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19
target-mips/translate.c
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@ -10531,14 +10531,25 @@ static void gen_rdhwr(DisasContext *ctx, int rt, int rd)
tcg_temp_free(t0);
}
static inline void clear_branch_hflags(DisasContext *ctx)
{
ctx->hflags &= ~MIPS_HFLAG_BMASK;
if (ctx->bstate == BS_NONE) {
save_cpu_state(ctx, 0);
} else {
/* it is not safe to save ctx->hflags as hflags may be changed
in execution time by the instruction in delay / forbidden slot. */
tcg_gen_andi_i32(hflags, hflags, ~MIPS_HFLAG_BMASK);
}
}
static void gen_branch(DisasContext *ctx, int insn_bytes)
{
if (ctx->hflags & MIPS_HFLAG_BMASK) {
int proc_hflags = ctx->hflags & MIPS_HFLAG_BMASK;
/* Branches completion */
ctx->hflags &= ~MIPS_HFLAG_BMASK;
clear_branch_hflags(ctx);
ctx->bstate = BS_BRANCH;
save_cpu_state(ctx, 0);
/* FIXME: Need to clear can_do_io. */
switch (proc_hflags & MIPS_HFLAG_BMASK_BASE) {
case MIPS_HFLAG_FBNSLOT:
@ -10596,8 +10607,8 @@ static void gen_branch(DisasContext *ctx, int insn_bytes)
tcg_gen_exit_tb(0);
break;
default:
MIPS_DEBUG("unknown branch");
break;
fprintf(stderr, "unknown branch 0x%x\n", proc_hflags);
abort();
}
}
}