On 02/09/2013 03:16 PM, Borislav Petkov wrote:
From: Borislav Petkov <b...@suse.de>
We detect CPUID function support on each CPU and save it for later use,
obviating the need to play the toggle EFLAGS.ID game every time. C code
is looking at ->cpuid_level anyway.
Signed-off-by: Borislav Petkov <b...@suse.de>
---
arch/x86/kernel/head_32.S | 48 +++++++++++++++++++++++------------------------
1 file changed, 23 insertions(+), 25 deletions(-)
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index f4d919e2cd2b..534397ba226c 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -318,30 +318,37 @@ default_entry:
movl %eax,%cr0
/*
- * New page tables may be in 4Mbyte page mode and may
- * be using the global pages.
+ * Initialize EFLAGS. Some BIOSes leave bits like NT set. This would confuse
the
+ * debugger if this code is traced. Best to initialize before switching to
+ * protected mode. As a side effect, we clear DF too because GCC expects it so.
+ */
+ pushl $0
+ popfl
+
I wouldn't really call it a "side effect". Perhaps the right thing here
is to say something like "we want to start out with %eflags
unambiguously clear".
(Note also we have had to CLD earlier because we have already copied the
command line.)
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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