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Tue, 05 Dec 2023 06:11:23 -0800 (PST) Message-ID: Date: Tue, 5 Dec 2023 15:11:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] xen: make include/xen/unaligned.h usable on all architectures Content-Language: en-US To: Julien Grall Cc: Andrew Cooper , George Dunlap , Stefano Stabellini , Wei Liu , Arnd Bergmann , Juergen Gross , xen-devel@lists.xenproject.org References: <20231205100756.18920-1-jgross@suse.com> <20231205100756.18920-2-jgross@suse.com> <1984c65c-72d8-4850-9886-f2b0766224a5@xen.org> <96ed8aa3-f92f-4b33-a846-549cfda14548@xen.org> <3789ced7-e320-4e32-bda9-3039551a7117@suse.com> <652bdb77-6f2d-4fe0-9ae1-132be50962e3@xen.org> <57eb9981-26e6-4281-ab31-78fb5b7427b1@suse.com> From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 05.12.2023 15:01, Julien Grall wrote: > On 05/12/2023 13:59, Jan Beulich wrote: >> On 05.12.2023 14:46, Julien Grall wrote: >>> On 05/12/2023 13:41, Juergen Gross wrote: >>>> On 05.12.23 14:31, Julien Grall wrote: >>>>> Anyway, given you don't seem to have a use-case yet, I would simply to >>>>> consider to surround the declaration with an a config which can be >>>>> selected if unaligned access is supported. >>>> >>>> Like in xen/common/lzo.c et al? >>> >>> Just to clarify, I am suggesting to add in unaligned.h: >>> >>> #ifdef CONFIG_HAS_UNALIGNED_ACCESS >>> >>> your definitions >>> >>> #endif >> >> But that would be wrong: HAS_UNALIGNED_ACCESS would be there to indicate >> one does _not_ need any special accessors. > > I am guessing you are disagreeing on the name rather than the concept? > If so, what about CONFIG_UNALIGNED_ACCESS_ALLOWED? Not really, no. Of course the name needs to properly express the purpose. But I don't see why a Kconfig control would be appropriate here. You simply want to provide accessors to unaligned data. Nobody needs to use them, but when you have to, they ought to be there. A Kconfig control (of the name you suggested first) would be helpful to not penalize architectures which can do unaligned accesses without any helpers (in case the code generated through the helpers turned out sub-optimal). Jan