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target/arm: Take an exception if PC is misaligned

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For A64, any input to an indirect branch can cause this.

For A32, many indirect branch paths force the branch to be aligned,
but BXWritePC does not.  This includes the BX instruction but also
other interworking changes to PC.  Prior to v8, this case is UNDEFINED.
With v8, this is CONSTRAINED UNPREDICTABLE and may either raise an
exception or force align the PC.

We choose to raise an exception because we have the infrastructure,
it makes the generated code for gen_bx simpler, and it has the
possibility of catching more guest bugs.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Richard Henderson 2021-11-03 00:03:49 -04:00 • committed by Peter Maydell
parent 936a6b8603
commit ee03027a2c
6 changed files with 87 additions and 20 deletions
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1
target/arm/helper.h
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@ -47,6 +47,7 @@ DEF_HELPER_FLAGS_3(sel_flags, TCG_CALL_NO_RWG_SE,
DEF_HELPER_2(exception_internal, void, env, i32)
DEF_HELPER_4(exception_with_syndrome, void, env, i32, i32, i32)
DEF_HELPER_2(exception_bkpt_insn, void, env, i32)
DEF_HELPER_2(exception_pc_alignment, noreturn, env, tl)
DEF_HELPER_1(setend, void, env)
DEF_HELPER_2(wfi, void, env, i32)
DEF_HELPER_1(wfe, void, env)