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Mon, 16 Jun 2025 06:01:30 -0700 (PDT) Message-ID: Date: Mon, 16 Jun 2025 15:01:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: [PATCH v6 5/7] x86: control memset() and memcpy() inlining From: Jan Beulich To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= References: Content-Language: en-US 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-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1750079495255124100 Content-Type: text/plain; charset="utf-8" Stop the compiler from inlining non-trivial memset() and memcpy() (for memset() see e.g. map_vcpu_info() or kimage_load_segments() for examples). This way we even keep the compiler from using REP STOSQ / REP MOVSQ when we'd prefer REP STOSB / REP MOVSB (when ERMS is available). With gcc10 this yields a modest .text size reduction (release build) of around 2k. Unfortunately these options aren't understood by the clang versions I have readily available for testing with; I'm unaware of equivalents. Note also that using cc-option-add is not an option here, or at least I couldn't make things work with it (in case the option was not supported by the compiler): The embedded comma in the option looks to be getting in the way. Requested-by: Andrew Cooper Signed-off-by: Jan Beulich Reviewed-by: Jason Andryuk --- v3: Re-base. v2: New. --- The boundary values are of course up for discussion - I wasn't really certain whether to use 16 or 32; I'd be less certain about using yet larger values. A respective Linux patch [1] uses 256 ... Similarly whether to permit the compiler to emit REP STOSQ / REP MOVSQ for known size, properly aligned blocks is up for discussion. [1] https://lore.kernel.org/lkml/20250605164733.737543-1-mjguzik@gmail.com/= T/#u --- a/xen/arch/x86/arch.mk +++ b/xen/arch/x86/arch.mk @@ -58,6 +58,9 @@ endif $(call cc-option-add,CFLAGS_stack_boundary,CC,-mpreferred-stack-boundary= =3D3) export CFLAGS_stack_boundary =20 +CFLAGS +=3D $(call cc-option,$(CC),-mmemcpy-strategy=3Dunrolled_loop:16:no= align$(comma)libcall:-1:noalign) +CFLAGS +=3D $(call cc-option,$(CC),-mmemset-strategy=3Dunrolled_loop:16:no= align$(comma)libcall:-1:noalign) + ifeq ($(CONFIG_UBSAN),y) # Don't enable alignment sanitisation. x86 has efficient unaligned access= es, # and various things (ACPI tables, hypercall pages, stubs, etc) are wont-f= ix.