Re: [PATCH 2/6] contrib/plugins/cache: fix warning when compiling on 32bits host

[Alex Bennée]

Thomas Huth <thuth@redhat.com> writes:

> On 15/08/2024 01.36, Pierrick Bouvier wrote:
>> Found on debian stable (i386).
>> ../contrib/plugins/cache.c: In function 'vcpu_tb_trans':
>> ../contrib/plugins/cache.c:477:30: error: cast from pointer to integer of 
>> different size [-Werror=pointer-to-int-cast]
>>    477 |             effective_addr = (uint64_t) 
>> qemu_plugin_insn_haddr(insn);
>>        |
>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>> ---
>>   contrib/plugins/cache.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>> diff --git a/contrib/plugins/cache.c b/contrib/plugins/cache.c
>> index 512ef6776b7..82ed734d6d4 100644
>> --- a/contrib/plugins/cache.c
>> +++ b/contrib/plugins/cache.c
>> @@ -471,12 +471,12 @@ static void vcpu_tb_trans(qemu_plugin_id_t id, struct 
>> qemu_plugin_tb *tb)
>>       n_insns = qemu_plugin_tb_n_insns(tb);
>>       for (i = 0; i < n_insns; i++) {
>>           struct qemu_plugin_insn *insn = qemu_plugin_tb_get_insn(tb, i);
>> -        uint64_t effective_addr;
>> +        uintptr_t effective_addr;
>>             if (sys) {
>> -            effective_addr = (uint64_t) qemu_plugin_insn_haddr(insn);
>> +            effective_addr = (uintptr_t) qemu_plugin_insn_haddr(insn);
>>           } else {
>> -            effective_addr = (uint64_t) qemu_plugin_insn_vaddr(insn);
>> +            effective_addr = (uintptr_t)
>> qemu_plugin_insn_vaddr(insn);
>>           }
>
> Is this the right fix? I assume effective_addr stores an address of
> the guest, so if the guest is 64-bit and the host is 32-bit, you now
> lose the upper bits of the address...?

I think the problem is higher up, it was a mistake to have:

  void *qemu_plugin_insn_haddr(const struct qemu_plugin_insn *insn);

return *void, at least vaddr returns an explicit 64 bit value which can
hold everything (at a slight expense to 32bit emulation hosts, but
seriously stop doing that we've been in the 64bit world for some time
now).

>
> The casting for qemu_plugin_insn_vaddr is not required at all since it
> already returns an uint64_t, so you can remoe that one. For the haddr
> part, maybe do a double-cast:
>
>   effective_addr = (uint64_t)(uintptr_t)qemu_plugin_insn_haddr(insn)
>
> ?
>
>  Thomas

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro