---

yaml
---
r: 350215
b: refs/heads/master
c: 9efb58d
h: refs/heads/master
i:
  350213: 4b33185
  350211: b1960e2
  350207: 6c71417
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 166df91daf38f619d4ca90b58ff90983de6e40d2
+refs/heads/master: 9efb58de919efa8312861d454be014094f6f0ffc

trunk/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)