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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 X-purgate-ID: tlsNG-d62444/1782812280-D1EC21E0-F9332EF6/0/0 X-purgate-type: clean X-purgate-size: 1863 On 30.06.2026 11:31, Sergii Dmytruk wrote: > On Tue, Jun 30, 2026 at 09:17:59AM +0200, Jan Beulich wrote: >> On 30.06.2026 00:18, Sergii Dmytruk wrote: >>> On Thu, Jan 22, 2026 at 04:52:36PM +0100, Jan Beulich wrote: >>>>> --- a/xen/arch/x86/boot/x86_64.S >>>>> +++ b/xen/arch/x86/boot/x86_64.S >>>>> @@ -15,7 +15,33 @@ ENTRY(__high_start) >>>>> mov $XEN_MINIMAL_CR4,%rcx >>>>> mov %rcx,%cr4 >>>>> >>>>> - mov stack_start(%rip),%rsp >>>>> + test %ebx,%ebx >>>>> + cmovz stack_start(%rip), %rsp >>>>> + jz .L_stack_set >>>>> + >>>>> + /* APs only: get stack base from APIC ID saved in %esp. */ >>>>> + mov $-1, %rax >>>> >>>> Here and below 32-bit insn would do fine. However, ... >>> >>> Are all addresses guaraneed to be below 4 GiB? >> >> You use %rax as the loop induction variable, so there isn't any address >> in it? Plus you already use ... >> >>>>> + lea x86_cpu_to_apicid(%rip), %rcx >>>>> +1: >>>>> + add $1, %rax >>>>> + cmp $NR_CPUS, %eax >> >> ... as 32-bit insn here anyway. > > But %rcx contains an address and it is added to %rax for `cmp` (quoted > below). Well, to use SCAS you will need to change how you use registers. (IOW first you need to determine whether SCAS actually can be used here, and then - if it can - you will need to arrange register use to fit it.) > Also if an address can be larger than 4 GiB, REPNE SCASL will > have to be 64-bit which is incompatible with the lookup for a 32-bit > value (unless I'm missing an instruction form that takes 64-bit address > but compares 32-bit values). Address size and operand size can be controlled independently. By default the former is 64 bits, while the suffix ('L' here) indicates the operand size wanted. Jan