Re: [RFC PATCH] target/i386: allow access_ptr to force slow path on failed probe

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> On 8/8/24 02:02, Alex Bennée wrote:
>> When we are using TCG plugin memory callbacks probe_access_internal
>> will return TLB_MMIO to force the slow path for memory access. This
>> results in probe_access returning NULL but the x86 access_ptr function
>> happily accepts an empty haddr resulting in segfault hilarity.
>> Check for an empty haddr to prevent the segfault and enable plugins
>> to
>> track all the memory operations for the x86 save/restore helpers.
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2489
>> Fixes: 6d03226b42 (plugins: force slow path when plugins instrument memory ops)
>> ---
>>   target/i386/tcg/access.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>> diff --git a/target/i386/tcg/access.c b/target/i386/tcg/access.c
>> index 56a1181ea5..8ea5c453a0 100644
>> --- a/target/i386/tcg/access.c
>> +++ b/target/i386/tcg/access.c
>> @@ -58,6 +58,10 @@ static void *access_ptr(X86Access *ac, vaddr addr, unsigned len)
>>         assert(addr >= ac->vaddr);
>>   +    if (!ac->haddr1) {
>> +        return NULL;
>> +    }
>> +
>>   #ifdef CONFIG_USER_ONLY
>>       assert(offset <= ac->size1 - len);
>>       return ac->haddr1 + offset;
>
> You need to remove the test_ptr macro below as well.

So we fall-back to the slow path for linux-user as well?

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro