From 7a293cd7cc3b44ccb58accbf1d6801f021ded0a3 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 5 Mar 2018 03:44:48 -0500 Subject: [PATCH] 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. Backports commit 5b8d7289e9e92a0d7bcecb93cd189e245fef10cd from qemu --- qemu/target/arm/translate.c | 27 ++++++--------------------- 1 file changed, 6 insertions(+), 21 deletions(-) diff --git a/qemu/target/arm/translate.c b/qemu/target/arm/translate.c index 4b4a3c39..0ac39aca 100644 --- a/qemu/target/arm/translate.c +++ b/qemu/target/arm/translate.c @@ -12083,29 +12083,14 @@ 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,