Re: [RFC PATCH] target/s390x: fake instruction loading when handling 'ex'

[Alex Bennée]

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> On 19/10/22 13:35, Alex Bennée wrote:
>> The s390x EXecute instruction is a bit weird as we synthesis the
>> executed instruction from what we have stored in memory. When plugins
>> are enabled this breaks because we detect the ld_code2() loading from
>> a non zero offset without the rest of the instruction being there.
>> Work around this with a special helper to inform the rest of the
>> translator about the instruction so things stay consistent.
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Cc: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   include/exec/translator.h    | 17 +++++++++++++++++
>>   target/s390x/tcg/translate.c |  4 ++++
>>   2 files changed, 21 insertions(+)
>> diff --git a/include/exec/translator.h b/include/exec/translator.h
>> index 3b77f5f4aa..156f568701 100644
>> --- a/include/exec/translator.h
>> +++ b/include/exec/translator.h
>> @@ -211,6 +211,23 @@ translator_ldq_swap(CPUArchState *env, DisasContextBase 
>> *db,
>>       return ret;
>>   }
>>   +/**
>> + * translator_fake_ldw - fake instruction load
>> + * @insn16: 2 byte instruction
>> + * @pc: program counter of instruction
>> + *
>> + * This is a special case helper used where the instruction we are
>> + * about to translate comes from somewhere else (e.g. being
>> + * re-synthesised for s390x "ex"). It ensures we update other areas of
>> + * the translator with details of the executed instruction.
>> + */
>> +
>> +static inline void translator_fake_ldw(uint16_t insn16, abi_ptr pc)
>> +{
>> +    plugin_insn_append(pc, &insn16, sizeof(insn16));
>> +}
>> +
>> +
>>   /*
>>    * Return whether addr is on the same page as where disassembly started.
>>    * Translators can use this to enforce the rule that only single-insn
>> diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
>> index 1d2dddab1c..a07b8b2d23 100644
>> --- a/target/s390x/tcg/translate.c
>> +++ b/target/s390x/tcg/translate.c
>> @@ -6317,12 +6317,16 @@ static const DisasInsn *extract_insn(CPUS390XState 
>> *env, DisasContext *s)
>>       if (unlikely(s->ex_value)) {
>>           /* Drop the EX data now, so that it's clear on exception paths.  */
>>           TCGv_i64 zero = tcg_const_i64(0);
>> +        int i;
>>           tcg_gen_st_i64(zero, cpu_env, offsetof(CPUS390XState, ex_value));
>>           tcg_temp_free_i64(zero);
>>             /* Extract the values saved by EXECUTE.  */
>>           insn = s->ex_value & 0xffffffffffff0000ull;
>>           ilen = s->ex_value & 0xf;
>> +        for (i = 0; i < ilen; i += 2) {
>
> Is it worth guarding with #ifdef CONFIG_PLUGIN?

I don't think so. It all gets nicely dead coded away when plugins aren't
enabled.

>
>> +            translator_fake_ldw(extract64(insn, 48 - (i * 8), 16), pc + i);
>> +        }
>>           op = insn >> 56;
>>       } else {
>>           insn = ld_code2(env, s, pc);


-- 
Alex Bennée