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x86: make lazy %gs optional on x86_32

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Impact: pt_regs changed, lazy gs handling made optional, add slight
        overhead to SAVE_ALL, simplifies error_code path a bit

On x86_32, %gs hasn't been used by kernel and handled lazily.  pt_regs
doesn't have place for it and gs is saved/loaded only when necessary.
In preparation for stack protector support, this patch makes lazy %gs
handling optional by doing the followings.

* Add CONFIG_X86_32_LAZY_GS and place for gs in pt_regs.

* Save and restore %gs along with other registers in entry_32.S unless
  LAZY_GS.  Note that this unfortunately adds "pushl $0" on SAVE_ALL
  even when LAZY_GS.  However, it adds no overhead to common exit path
  and simplifies entry path with error code.

* Define different user_gs accessors depending on LAZY_GS and add
  lazy_save_gs() and lazy_load_gs() which are noop if !LAZY_GS.  The
  lazy_*_gs() ops are used to save, load and clear %gs lazily.

* Define ELF_CORE_COPY_KERNEL_REGS() which always read %gs directly.

xen and lguest changes need to be verified.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Tejun Heo
2009-02-09 22:17:40 +09:00
committed by Ingo Molnar
parent d9a89a26e0
commit ccbeed3a05
11 changed files with 158 additions and 40 deletions
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5
arch/x86/kernel/ptrace.c
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@@ -75,10 +75,7 @@ static inline bool invalid_selector(u16 value)
static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long regno)
{
BUILD_BUG_ON(offsetof(struct pt_regs, bx) != 0);
regno >>= 2;
if (regno > FS)
--regno;
return &regs->bx + regno;
return &regs->bx + (regno >> 2);
}
static u16 get_segment_reg(struct task_struct *task, unsigned long offset)