target/i386: Make translator stop before the end of a page

target/i386: Make translator stop before the end of a page

Right now translator stops right *after* the end of a page, which
breaks reporting of fault locations when the last instruction of a
multi-insn translation block crosses a page boundary.

An implementation, like the one arm and s390x have, would require an
i386 length disassembler, which is burdensome to maintain. Another
alternative would be to single-step at the end of a guest page, but
this may come with a performance impact.

Fix by snapshotting disassembly state and restoring it after we figure
out we crossed a page boundary. This includes rolling back cc_op
updates and emitted ops.

Signed-off-by: Ilya Leoshkevich <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1143
Message-Id: <20220817150506[email protected]>
[rth: Simplify end-of-insn cross-page checks.]
Signed-off-by: Richard Henderson <[email protected]>