On 03/24/2015 07:43 PM, Ingo Molnar wrote: > From 0229a184997a7d4ad4398ee3ac2f5ae78c1c1a03 Mon Sep 17 00:00:00 2001 > From: Ingo Molnar <[email protected]> > Date: Tue, 24 Mar 2015 18:57:13 +0100 > Subject: [PATCH] x86/asm/entry/64: Improve the THREAD_INFO() macro explanation > > Explain the background, and add a real example. > > Cc: Alexei Starovoitov <[email protected]> > Cc: Andy Lutomirski <[email protected]> > Cc: Andy Lutomirski <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Denys Vlasenko <[email protected]> > Cc: Frederic Weisbecker <[email protected]> > Cc: H. Peter Anvin <[email protected]> > Cc: Kees Cook <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Oleg Nesterov <[email protected]> > Cc: Steven Rostedt <[email protected]> > Cc: Will Drewry <[email protected]> > Signed-off-by: Ingo Molnar <[email protected]> > --- > arch/x86/include/asm/thread_info.h | 27 +++++++++++++++++++++++---- > 1 file changed, 23 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/thread_info.h > b/arch/x86/include/asm/thread_info.h > index ad0ee3423da5..813dfbb867a7 100644 > --- a/arch/x86/include/asm/thread_info.h > +++ b/arch/x86/include/asm/thread_info.h > @@ -206,10 +206,29 @@ static inline unsigned long current_stack_pointer(void) > _ASM_SUB $(THREAD_SIZE),reg ; > > /* > - * ASM operand which evaluates to thread_info address > - * if it is known that "reg" is exactly "off" bytes below stack top. > - * Example (fetch thread_info->fieldname): > - * mov TI_fieldname+THREAD_INFO(reg, off),%eax > + * ASM operand which evaluates to a 'thread_info' address of > + * the current task, if it is known that "reg" is exactly "off" > + * bytes below the top of the stack currently. > + * > + * ( The kernel stack's size is known at build time, it is usually > + * 2 or 4 pages, and the bottom of the kernel stack contains > + * the thread_info structure. So to access the thread_info very > + * quickly from assembly code we can calculate down from the > + * top of the kernel stack to the bottom, using constant, > + * build-time calculations only. ) > + * > + * For example, to fetch the current thread_info->flags value into %eax > + * on x86-64 defconfig kernels, in syscall entry code where RSP is > + * currently at exactly SIZEOF_PTREGS bytes away from the top of the > + * stack: > + * > + * mov TI_flags+THREAD_INFO(%rsp, SIZEOF_PTREGS), %eax > + * > + * will translate to: > + * > + * 8b 84 24 b8 c0 ff ff mov -0x3f48(%rsp), %eax > + * > + * which is below the current RSP by almost 16K. > */ > #define THREAD_INFO(reg, off) ((off)-THREAD_SIZE)(reg)
Acked-by: Denys Vlasenko <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
