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x86: Fix rflags in FAKE_STACK_FRAME

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The x86_64 kernel pushes the fake kernel stack in
arch/x86/kernel/entry_64.S:FAKE_STACK_FRAME, and
rflags register in it does not conform to the specification.

Although Intel's manual[1] says bit 1 of it shall be set to 1,
this bit is cleared to 0 on pushing the fake stack.

[1] Intel(R) 64 and IA-32 Architectures Software Developer's Manual
    Vol.1 3-21 Figure 3-8. EFLAGS Register

If it is not on purpose, it is better to be fixed, because
it can lead some tools misunderstanding the stack frame. For example,
"crash" utility[2] actually detects it and warns you like
below:

       RIP: ffffffff8005dfa2  RSP: ffff8104ce0c7f58  RFLAGS: 00000200
       [...]

       bt: WARNING: possibly bogus exception frame

Signed-off-by: Seiichi Ikarashi <[email protected]>
Tested-by: Masayoshi MIZUMA <[email protected]>
Cc: Jan Beulich <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Linus Torvalds <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Seiichi Ikarashi 2011-12-06 17:58:14 +09:00 • committed by Ingo Molnar
commit 1cf8343f55
4 changed files with 4 additions and 3 deletions
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2
drivers/lguest/x86/core.c
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@ -697,7 +697,7 @@ void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start)
* interrupts are enabled. We always leave interrupts enabled while
* running the Guest.
*/
regs->eflags = X86_EFLAGS_IF | 0x2;
regs->eflags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
/*
* The "Extended Instruction Pointer" register says where the Guest is