diff options
| author | Peter Maydell <peter.maydell@linaro.org> | 2017-10-09 14:48:37 +0100 |
|---|---|---|
| committer | Peter Maydell <peter.maydell@linaro.org> | 2017-10-12 13:23:14 +0100 |
| commit | 5b8d7289e9e92a0d7bcecb93cd189e245fef10cd (patch) | |
| tree | ce5d0e090280463843614016f6d1fd36619930ce | |
| parent | 296e5a0a6c393553079a641c50521ae33ff89324 (diff) | |
target-arm: Simplify insn_crosses_page()
Recent changes have left insn_crosses_page() more complicated
than it needed to be:
* it's only called from thumb_tr_translate_insn() so we know
for certain that we're looking at a Thumb insn
* the caller's check for dc->pc >= dc->next_page_start - 3
means that dc->pc can't possibly be 4 aligned, so there's
no need to check that (the check was partly there to ensure
that we didn't treat an ARM insn as Thumb, I think)
* we now have thumb_insn_is_16bit() which lets us do a precise
check of the length of the next insn, rather than opencoding
an inaccurate check
Simplify it down to just loading the first half of the insn
and calling thumb_insn_is_16bit() on it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1507556919-24992-8-git-send-email-peter.maydell@linaro.org
| -rw-r--r-- | target/arm/translate.c | 27 |
1 files changed, 6 insertions, 21 deletions
diff --git a/target/arm/translate.c b/target/arm/translate.c index 19c136c651..a5abdfa420 100644 --- a/target/arm/translate.c +++ b/target/arm/translate.c @@ -11872,29 +11872,14 @@ static bool insn_crosses_page(CPUARMState *env, DisasContext *s) { /* Return true if the insn at dc->pc might cross a page boundary. * (False positives are OK, false negatives are not.) + * We know this is a Thumb insn, and our caller ensures we are + * only called if dc->pc is less than 4 bytes from the page + * boundary, so we cross the page if the first 16 bits indicate + * that this is a 32 bit insn. */ - uint16_t insn; + uint16_t insn = arm_lduw_code(env, s->pc, s->sctlr_b); - if ((s->pc & 3) == 0) { - /* At a 4-aligned address we can't be crossing a page */ - return false; - } - - /* This must be a Thumb insn */ - insn = arm_lduw_code(env, s->pc, s->sctlr_b); - - if ((insn >> 11) >= 0x1d) { - /* Top five bits 0b11101 / 0b11110 / 0b11111 : this is the - * First half of a 32-bit Thumb insn. Thumb-1 cores might - * end up actually treating this as two 16-bit insns (see the - * code at the start of disas_thumb2_insn()) but we don't bother - * to check for that as it is unlikely, and false positives here - * are harmless. - */ - return true; - } - /* Definitely a 16-bit insn, can't be crossing a page. */ - return false; + return !thumb_insn_is_16bit(s, insn); } static int arm_tr_init_disas_context(DisasContextBase *dcbase, |