joncampbell123/dosbox-x
1
0
Fork 0
mirror of https://github.com/joncampbell123/dosbox-x.git synced 2025-10-14 02:17:36 +08:00
Code Issues Packages Projects Releases Wiki Activity

Update CPUID to always return SEP set for Pentium II, and to signal availability through the stepping number, because Intel set a feature bit not actually implemented until a later model, and OSes will not attempt SYSENTER unless stepping 3 or higher

Browse Source
This commit is contained in:
Jonathan Campbell
2021-11-22 07:34:34 -08:00
parent 2d28bd963e
commit 853611aef7
1 changed files with 17 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
src/cpu/cpu.cpp
View File

@@ -2956,13 +2956,28 @@ bool CPU_CPUID(void) {
if (enable_msr) reg_edx |= 0x20; /* ModelSpecific/MSR */
if (enable_cmpxchg8b) reg_edx |= 0x100; /* CMPXCHG8B */
} else if (CPU_ArchitectureType == CPU_ARCHTYPE_PENTIUMII || CPU_ArchitectureType == CPU_ARCHTYPE_EXPERIMENTAL) {
reg_eax=0x632; /* intel pentium II */
/* NTS: Most operating systems will not attempt SYSENTER/SYSEXIT unless this returns model 3, stepping 3, or higher. */
/* From Intel [https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-2b-manual.pdf]:
*
* "The SYSENTER and SYSEXIT instructions were introduced into the IA-32 architecture in the Pentium II processor."
*
* "An operating system that qualifies the SEP flag must also qualify the processor family and model to ensure that
* the SYSENTER/SYSEXIT instructions are actually present"
*
* "When the CPUID instruction is executed on the Pentium Pro processor (model 1), the processor returns a the SEP
* flag as set, but does not support the SYSENTER/SYSEXIT instructions."
*
* Therefore, always return with bit 11 (SEP) set whether or not SYSCALL is enabled because Intel made a stupid mistake.
*
* This website [https://www.geoffchappell.com/studies/windows/km/cpu/sep.htm?tx=256] notes how the Windows NT kernel
* follows this rule, and the Linux kernel does too */
reg_eax=enable_syscall?0x633:0x631; /* intel pentium II */
reg_ebx=0; /* Not Supported */
reg_ecx=0; /* No features */
reg_edx=0x00008011; /* FPU+TimeStamp/RDTSC */
if (enable_msr) reg_edx |= 0x20; /* ModelSpecific/MSR */
if (enable_cmpxchg8b) reg_edx |= 0x100; /* CMPXCHG8B */
if (enable_syscall) reg_edx |= 0x800; /* SEP Fast System Call aka SYSENTER/SYSEXIT */
reg_edx |= 0x800; /* SEP Fast System Call aka SYSENTER/SYSEXIT [SEE NOTES AT TOP OF THIS IF STATEMENT] */
} else {
return false;
}