Acked-by: Andy Lutomirski <[email protected]> On Tue, Mar 24, 2015 at 11:50 AM, Denys Vlasenko <[email protected]> wrote: > 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]> >
-- Andy Lutomirski AMA Capital Management, LLC -- 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/
