diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index a9c5cc851285ad02e9ea0ee7a361ebd51ce3ceda..e3725a0f43274e5556725c1eacce2a9e639f469b 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -307,30 +307,39 @@ default_entry: movl %eax,%cr0 /* - * New page tables may be in 4Mbyte page mode and may - * be using the global pages. + * We want to start out with EFLAGS unambiguously cleared. Some BIOSes leave + * bits like NT set. This would confuse the debugger if this code is traced. So + * initialize them properly now before switching to protected mode. That means + * DF in particular (even though we have cleared it earlier after copying the + * command line) because GCC expects it. + */ + pushl $0 + popfl + +/* + * New page tables may be in 4Mbyte page mode and may be using the global pages. * - * NOTE! If we are on a 486 we may have no cr4 at all! - * Specifically, cr4 exists if and only if CPUID exists - * and has flags other than the FPU flag set. + * NOTE! If we are on a 486 we may have no cr4 at all! Specifically, cr4 exists + * if and only if CPUID exists and has flags other than the FPU flag set. */ + movl $-1,pa(X86_CPUID) # preset CPUID level movl $X86_EFLAGS_ID,%ecx pushl %ecx - popfl - pushfl - popl %eax - pushl $0 - popfl + popfl # set EFLAGS=ID pushfl - popl %edx - xorl %edx,%eax - testl %ecx,%eax - jz 6f # No ID flag = no CPUID = no CR4 + popl %eax # get EFLAGS + testl $X86_EFLAGS_ID,%eax # did EFLAGS.ID remained set? + jz 6f # hw disallowed setting of ID bit + # which means no CPUID and no CR4 + + xorl %eax,%eax + cpuid + movl %eax,pa(X86_CPUID) # save largest std CPUID function movl $1,%eax cpuid - andl $~1,%edx # Ignore CPUID.FPU - jz 6f # No flags or only CPUID.FPU = no CR4 + andl $~1,%edx # Ignore CPUID.FPU + jz 6f # No flags or only CPUID.FPU = no CR4 movl pa(mmu_cr4_features),%eax movl %eax,%cr4 @@ -377,14 +386,6 @@ default_entry: /* Shift the stack pointer to a virtual address */ addl $__PAGE_OFFSET, %esp -/* - * Initialize eflags. Some BIOS's leave bits like NT set. This would - * confuse the debugger if this code is traced. - * XXX - best to initialize before switching to protected mode. - */ - pushl $0 - popfl - /* * start system 32-bit setup. We need to re-do some of the things done * in 16-bit mode for the "real" operations. @@ -461,7 +462,6 @@ is486: movl $0x50022,%ecx # set AM, WP, NE and MP xorl %eax,%eax # Clear LDT lldt %ax - cld # gcc2 wants the direction flag cleared at all times pushl $0 # fake return address for unwinder jmp *(initial_code)