On 19.01.2014, at 17:51, Peter Maydell <peter.mayd...@linaro.org> wrote:
> On 19 January 2014 16:32, Alexander Graf <ag...@suse.de> wrote:
>> When QEMU gets compiled with --enable-debug-tcg we can check for temporary
>> leakage. Implement the necessary target code for this and fail emulation
>> when we hit a leakage.
>>
>> This hopefully ensures that we don't get new leaks.
>>
>> Signed-off-by: Alexander Graf <ag...@suse.de>
>> ---
>> target-ppc/translate.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/target-ppc/translate.c b/target-ppc/translate.c
>> index 02cd18e..759133c 100644
>> --- a/target-ppc/translate.c
>> +++ b/target-ppc/translate.c
>> @@ -10412,6 +10412,7 @@ static inline void
>> gen_intermediate_code_internal(PowerPCCPU *cpu,
>> max_insns = CF_COUNT_MASK;
>>
>> gen_tb_start();
>> + tcg_clear_temp_count();
>> /* Set env in case of segfault during code fetch */
>> while (ctx.exception == POWERPC_EXCP_NONE
>> && tcg_ctx.gen_opc_ptr < gen_opc_end) {
>> @@ -10511,6 +10512,12 @@ static inline void
>> gen_intermediate_code_internal(PowerPCCPU *cpu,
>> */
>> break;
>> }
>> + if (tcg_check_temp_count()) {
>> + fprintf(stderr, "Opcode %02x %02x %02x (%08x) leaked
>> temporaries\n",
>> + opc1(ctx.opcode), opc2(ctx.opcode), opc3(ctx.opcode),
>> + ctx.opcode);
>> + exit(1);
>
> Exiting is pretty harsh; ARM just warns and continues. In my
> experience most of the TCG temp leaks happen on paths
> where the decoder has done some setup, then discovered
> later that the instruction should throw an exception and
> the exception generating code path exits the decoder function
> early without freeing the TCG temp. Since we always finish
> the TB immediately in this case, it's never possible to actually
> run out of TCG temporaries. So I felt that continuing was better
> than gratuitously stopping the guest from running in these cases,
> since it's hard to be certain you've caught them all unless you
> care to run the decoder through the complete set of instructions
> from 0x00000000 to 0xffffffff. (That is actually possible in less
> than geological time if you write a special purpose test harness.)
Well, the check only ever happens when QEMU gets compiled with
--enable-debug-tcg, so I figured it's easier for me to catch new problems or
problems with unit tests if we get a harsh abort :).
Alex
