linux-kernel - processor flags

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Date:	Thu, 27 Mar 2008 22:47:49 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: processor flags

Hi Peter, Ingo

could you spend a few minutes on me? ;)

You know, I'm almost complete changing the vm86 flags
with X86_EFLAGS_... but there is a hidden problem lays.
Look, in vm86.h we have the definition

#ifdef CONFIG_VM86
#define VM_MASK		0x00020000
#else
#define VM_MASK		0 /* ignored */
#endif

which has an indirect conditional compilation effect.
For example, if we take a look on include/asm-x86/ptrace.h

	static inline int v8086_mode(struct pt_regs *regs)
	{
	#ifdef CONFIG_X86_32
		return (regs->flags & VM_MASK);
	#else
		return 0;	/* No V86 mode support in long mode */
	#endif
	}

so if we don't have CONFIG_VM86 defined this function *always*
returning 0 so there I can't just change VM_MASK to X86_EFLAGS_VM.

Another piece of code from traps_32.c:do_general_protection

	if (regs->flags & VM_MASK)
		goto gp_in_vm86;

so if we didn't set CONFIG_VM86 i think this part is just thrown out
by gcc. So as we see, this VM_MASK original flag is not *just* a flag
but also says gcc which part of code to compile.

And now I'm in confusion - the way of changing this code I see is the
following:

- or use additional #ifdef CONFIG_VM86 in code where VM_MASK is used
  (that would be ugly IMHO)
- rename VM_MASK to say X86_EFLAGS_VM86 with that #ifdef remained
- rest VM_MASK as it is

How do you think?

		- Cyrill -
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