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Wed, 24 Jul 2024 02:16:53 -0700 (PDT) Message-ID: Date: Wed, 24 Jul 2024 11:16:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH for-4.19] x86/altcall: fix clang code-gen when using altcall in loop constructs To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: Alejandro Vallejo , xen-devel@lists.xenproject.org, Andrew Cooper , Oleksii Kurochko References: <20240723093117.99487-1-roger.pau@citrix.com> <7a5da6ce-0ef0-4666-a5c4-44383469f67e@suse.com> <4a1bae1e-16d2-4536-b69a-1fff8179ee86@suse.com> Content-Language: en-US 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: 8bit On 24.07.2024 11:13, Roger Pau Monné wrote: > On Wed, Jul 24, 2024 at 10:41:43AM +0200, Jan Beulich wrote: >> On 24.07.2024 10:28, Roger Pau Monné wrote: >>> The only way I've found to cope with this is to use something like: >>> >>> #define ALT_CALL_ARG(arg, n) \ >>> union { \ >>> typeof(arg) e[(sizeof(long) + sizeof(arg) - 1) / sizeof(arg)]; \ >>> unsigned long r; \ >>> } a ## n ## __ = { \ >>> .e[0] = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); })\ >>> }; \ >>> register unsigned long a ## n ## _ asm ( ALT_CALL_arg ## n ) = \ >>> a ## n ## __.r >>> >>> An oversized array that ensures all the space of the long is covered >>> by the array, but then we need an extra variable, as we would >>> otherwise require modifying ALT_CALL{0..6}_OUT to use aX_.r instead of >>> aX_. >> >> I don't think we need to over-size the array. It just gets yet a little >> more complex then: >> >> #define ALT_CALL_ARG(arg, n) \ >> register union { \ >> struct { \ >> typeof(arg) e; \ >> char pad[sizeof(long) - sizeof(arg)]; \ >> } s; \ >> unsigned long r; \ >> } a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \ >> .s.e = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); }) \ >> } > > We could even simplify this, there's no need for the union anymore, > since struct size == sizeof(long) already: > > #define ALT_CALL_ARG(arg, n) \ > register struct { \ > typeof(arg) e; \ > char pad[sizeof(long) - sizeof(arg)]; \ > } a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \ > .e = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); }) \ > } > > The above seems to work for both the original issue and the new one. Oh, good. If the compiler's happy with not being dealt an unsigned long, even better. Maybe for consistency we want to use sizeof(void *) also in pad's definition then. Jan