On Thu, Apr 28, 2016 at 1:44 PM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > Thanks to all the recent x86 entry code refactoring, most tasks' kernel > stacks start at the same offset right above their saved pt_regs, > regardless of which syscall was used to enter the kernel. That creates > a nice convention which makes it straightforward to identify the > "bottom" of the stack, which can be useful for stack walking code which > needs to verify the stack is sane. > > However there are still a few types of tasks which don't yet follow that > convention: > > 1) CPU idle tasks, aka the "swapper" tasks > > 2) freshly forked TIF_FORK tasks which don't have a stack at all > > Make the idle tasks conform to the new stack bottom convention by > starting their stack at a sizeof(pt_regs) offset from the end of the > stack page. > > Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > --- > arch/x86/kernel/head_64.S | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S > index 6dbd2c0..0b12311 100644 > --- a/arch/x86/kernel/head_64.S > +++ b/arch/x86/kernel/head_64.S > @@ -296,8 +296,9 @@ ENTRY(start_cpu) > * REX.W + FF /5 JMP m16:64 Jump far, absolute indirect, > * address given in m16:64. > */ > - movq initial_code(%rip),%rax > - pushq $0 # fake return address to stop unwinder > + call 1f # put return address on stack for unwinder > +1: xorq %rbp, %rbp # clear frame pointer > + movq initial_code(%rip), %rax > pushq $__KERNEL_CS # set correct cs > pushq %rax # target address in negative space > lretq > @@ -325,7 +326,7 @@ ENDPROC(start_cpu0) > GLOBAL(initial_gs) > .quad INIT_PER_CPU_VAR(irq_stack_union) > GLOBAL(initial_stack) > - .quad init_thread_union+THREAD_SIZE-8 > + .quad init_thread_union + THREAD_SIZE - SIZEOF_PTREGS As long as you're doing this, could you also set orig_ax to -1? I remember running into some oddities resulting from orig_ax containing garbage at some point. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
