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From: "Mattias Rönnblom" <hofors@lysator.liu.se>
To: Bruce Richardson <bruce.richardson@intel.com>,
	Tyler Retzlaff <roretzla@linux.microsoft.com>
Cc: "Morten Brørup" <mb@smartsharesystems.com>,
	dev@dpdk.org, "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
	"Anatoly Burakov" <anatoly.burakov@intel.com>,
	"David Christensen" <drc@linux.vnet.ibm.com>,
	"Harry van Haaren" <harry.van.haaren@intel.com>,
	"Konstantin Ananyev" <konstantin.v.ananyev@yandex.ru>,
	"Min Zhou" <zhoumin@loongson.cn>,
	"Ruifeng Wang" <ruifeng.wang@arm.com>,
	"Stanislaw Kardach" <kda@semihalf.com>,
	thomas@monjalon.net
Subject: Re: [PATCH] RFC: use C11 alignas instead of GCC attribute aligned
Date: Tue, 30 Jan 2024 19:18:46 +0100	[thread overview]
Message-ID: <948697d6-53a4-424c-a761-6da1a1cbed02@lysator.liu.se> (raw)
In-Reply-To: <Zbk4_cI3niWzhc1-@bricha3-MOBL.ger.corp.intel.com>

On 2024-01-30 18:59, Bruce Richardson wrote:
> On Tue, Jan 30, 2024 at 09:39:28AM -0800, Tyler Retzlaff wrote:
>> On Tue, Jan 30, 2024 at 09:08:21AM +0100, Mattias Rönnblom wrote:
> <snip>
>>>
>>> Sorry if I've missed some discussion on the list, but the current
>>> pattern of putting __rte_aligned(X) at the end doesn't work with MSVC,
>>> or why are we doing this? C11 purism doesn't seem like much of a
>>> driving force.
>>
>> __rte_aligned(X) at the end doesn't work with MSVC __declspec(align(n))
>>
>>>
>>> If one defined a macro as __declspec(align(X)) on MSVC and
>>> __attribute__(__aligned__(X)) on other compilers, could it do the work
>>> of both the above RTE_ALIGNAS() and RTE_ALIGN_TYPE()?
>>>
>>> <a> struct <b> { int a; } <c>;
>>
>> yes for struct/union. but only when placed at location you mark as <b>
>> when compiling both C and C++ for all toolchains.
>>
> I can see this restriction on placement potentially causing problems. Maybe
> we should consider defining macros with the "struct" keywork included. For
> example, (using gcc attributes here):
> 
> #define rte_aligned_struct(n) struct __attribute((aligned(n)))
> 
> rte_aligned_struct my_struct {
> 	int a;
> }
> 
> Probably that's taking things a bit far away from standard C, but it may
> cut down on placement errors.

It doesn't go well with the fact alignment is just one of several 
attributes one may want to add to a struct (__rte_packed is another).

A quick scan of the DPDK source tree suggests DPDK developers are pretty 
good at putting the old __rte_cache_aligned consistently after the 
struct declaration (i.e., position <c> per above). Conservative as they 
may be, perhaps they could be rewired to consistently put it somewhere else.

  parent reply	other threads:[~2024-01-30 18:18 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-15 17:39 Tyler Retzlaff
2023-11-15 17:39 ` [PATCH] eal: " Tyler Retzlaff
2023-11-15 18:13   ` Bruce Richardson
2023-11-15 18:27     ` Tyler Retzlaff
2023-11-15 20:08   ` Morten Brørup
2023-11-15 21:03     ` Tyler Retzlaff
2023-11-15 22:43       ` Stanisław Kardach
2023-11-16 10:12   ` Mattias Rönnblom
2024-01-25 18:37 ` [PATCH] RFC: " Tyler Retzlaff
2024-01-25 22:53   ` Morten Brørup
2024-01-25 23:31     ` Tyler Retzlaff
2024-01-26 10:05     ` Mattias Rönnblom
2024-01-26 10:18       ` Morten Brørup
2024-01-27 19:15         ` Mattias Rönnblom
2024-01-28  8:57           ` Morten Brørup
2024-01-28 10:00             ` Mattias Rönnblom
2024-01-29 19:43               ` Tyler Retzlaff
2024-01-30  8:08                 ` Mattias Rönnblom
2024-01-30 17:39                   ` Tyler Retzlaff
2024-01-30 17:59                     ` Bruce Richardson
2024-01-30 18:01                       ` Bruce Richardson
2024-01-30 18:04                       ` Tyler Retzlaff
2024-01-30 18:18                       ` Mattias Rönnblom [this message]
2024-01-31 16:04                     ` Mattias Rönnblom
2024-01-30  8:09                 ` Morten Brørup
2024-01-30  9:28                   ` Mattias Rönnblom
2024-01-30 10:17                     ` Morten Brørup
2024-01-30 13:00                       ` Morten Brørup
2024-01-30 17:54                   ` Tyler Retzlaff

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