On 2023-03-21 06:15, Ondřej Surý wrote:
On 20. 3. 2023, at 19:31, Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
wrote:
On 2023-03-17 17:37, Ondřej Surý via lttng-dev wrote:
When adding REMOVED_FLAG to the pointers in the rculfhash
implementation, retype the generic pointer to uintptr_t to fix the
compiler error.
What is the compiler error ? I'm wondering whether the expected choice
to match the rest of this file's content would be to use "uintptr_t *" or "unsigned
long *" ?
This is the error:
rculfhash.c:1201:2: error: address argument to atomic operation must be a
pointer to integer ('struct cds_lfht_node **' invalid)
uatomic_or(&node->next, REMOVED_FLAG);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/urcu/uatomic.h:60:8: note: expanded from macro 'uatomic_or'
(void)__atomic_or_fetch((addr), (mask), __ATOMIC_RELAXED)
^ ~~~~~~
rculfhash.c:1444:3: error: address argument to atomic operation must be a
pointer to integer ('struct cds_lfht_node **' invalid)
uatomic_or(&fini_bucket->next, REMOVED_FLAG);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/urcu/uatomic.h:60:8: note: expanded from macro 'uatomic_or'
(void)__atomic_or_fetch((addr), (mask), __ATOMIC_RELAXED)
^ ~~~~~~
uintptr_t is defined as "unsigned integer type capable of holding a pointer to
void" while unsigned long is at least 32-bit;
I guess that works in a practise, but using unsigned long to retype the
pointers might blow up (thinking of x32 which I know
little about, but it's kind of hybrid architecture, isn't it?)
x32 uses 4 bytes for unsigned long, uintptr_t, and void * size. So even
that architecture is OK with casting pointer to unsigned long.
I agree with you that uintptr_t is the semantically correct type, but it
should come as a separate change across the urcu code base: currently
there are many places where void * is cast to unsigned long to do
bitwise operations.
I therefore recommend to use unsigned long here to stay similar to the
rest of the code base, and keep the transition from unsigned long to
uintptr_t for the future, as it is not an immediate issue we have to
address.
Thanks,
Mathieu
Ondrej
--
Ondřej Surý (He/Him)
ond...@sury.org
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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