From: Mathieu Desnoyers via lttng-dev <lttng-dev@lists.lttng.org>
To: "Ondřej Surý" <ondrej@sury.org>
Cc: lttng-dev@lists.lttng.org
Subject: Re: [lttng-dev] [PATCH 6/7] Fix: uatomic_or() need retyping to uintptr_t in rculfhash.c
Date: Tue, 21 Mar 2023 10:44:12 -0400 [thread overview]
Message-ID: <b4b783ec-6d57-e658-7ac9-84e5a996b8b3@efficios.com> (raw)
In-Reply-To: <25F238AC-69EB-47BB-BEAF-B513C44B652E@sury.org>
On 2023-03-21 06:15, Ondřej Surý wrote:
>
>> On 20. 3. 2023, at 19:31, Mathieu Desnoyers <mathieu.desnoyers@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)
> ondrej@sury.org
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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next prev parent reply other threads:[~2023-03-21 14:44 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-17 21:37 [lttng-dev] [PATCH 0/7] Replace the custom code with gcc/clang __atomic builtins Ondřej Surý via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 1/7] Require __atomic builtins to build Ondřej Surý via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 2/7] Use gcc __atomic builtis for <urcu/uatomic.h> implementation Ondřej Surý via lttng-dev
2023-03-20 18:03 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:13 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:28 ` Ondřej Surý via lttng-dev
2023-03-20 18:38 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:41 ` Mathieu Desnoyers via lttng-dev
2023-03-20 19:38 ` Duncan Sands via lttng-dev
2023-03-21 20:26 ` Mathieu Desnoyers via lttng-dev
2023-03-22 8:24 ` Duncan Sands via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 3/7] Use __atomic_thread_fence() for cmm_barrier() Ondřej Surý via lttng-dev
2023-03-20 18:06 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:14 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 4/7] Replace the internal pointer manipulation with __atomic builtins Ondřej Surý via lttng-dev
2023-03-20 18:25 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 5/7] Use __atomic builtins to implement CMM_{LOAD, STORE}_SHARED Ondřej Surý via lttng-dev
2023-03-20 18:28 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 6/7] Fix: uatomic_or() need retyping to uintptr_t in rculfhash.c Ondřej Surý via lttng-dev
2023-03-20 18:31 ` Mathieu Desnoyers via lttng-dev
2023-03-21 10:15 ` Ondřej Surý via lttng-dev
2023-03-21 14:44 ` Mathieu Desnoyers via lttng-dev [this message]
2023-03-21 14:45 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 7/7] Experiment: Add explicit memory barrier in free_completion() Ondřej Surý via lttng-dev
2023-03-20 18:37 ` Mathieu Desnoyers via lttng-dev
2023-03-21 10:21 ` Ondřej Surý via lttng-dev
2023-03-21 14:46 ` Mathieu Desnoyers via lttng-dev
2023-03-21 14:48 ` Ondřej Surý via lttng-dev
2023-03-21 14:49 ` Mathieu Desnoyers via lttng-dev
2023-03-21 14:59 ` [lttng-dev] TSAN and the tests Ondřej Surý via lttng-dev
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