[Crash-utility] Re: [PATCH] x86_64: Add top_of_kernel_stack_padding for kernel stack

> > With kernel patch [1], x86_64 will add extra padding for kernel stack, > > as a result, the pt_regs will be shift down by the offset of padding. > > Without the patch, the values of registers read from pt_regs will be > > incorrect. > > > > Though currently the TOP_OF_KERNEL_STACK_PADDING is configured by > > Kconfig, according to kernel code comment [2], the value may be made > > dynamicly later. In addition there might be systems compiled without > > Kconfig avaliable. So in this patch, we will calculate the value of > > TOP_OF_KERNEL_STACK_PADDING. > > > > The calculation is as follows: > > > > 1) in startup_64(), there is a lea instruction as: > >     leaq (__end_init_task - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE)(%rip), %rsp > > > > 2) in rewind_stack_and_make_dead(), there is a lea instruction as: > >     leaq      -PTREGS_SIZE(%rax), %rsp > > > > The disassembled 2 instructions will be like: > > > > 1) 0xffffffff93a0007d <startup_64+3>:      lea    0x1e03ec4(%rip),%rsp        # 0xffffffff95803f48 > >                                                                                ^^^^^^^^^^^^^^^^^^^^ > > 2) 0xffffffff93a0465a <rewind_stack_and_make_dead+10>:     lea    -0xa8(%rax),%rsp > >                                                                     ^^^^ > > 0xffffffff95803f48 is the value of (__end_init_task - > > TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE), and 0xa8 is the value of > > PTREGS_SIZE, __end_init_task can be get by symbol reading. > > Calculating the value of TOP_OF_KERNEL_STACK_PADDING, which looks good, but it heavily relies on compiler. > Normally we would use this way unless there is no other choice. > > How about the following changes? Although it doesn't handle the case that the value is dynamic, let's see > how to change in the kernel in future, and then consider how to reflect it in crash-utility. > Sure, looks good to me, so let's go with this, and update it later when kernel changes. Ok. Thanks, Tao. Applied with minor changes: https://github.com/crash-utility/crash/commit/48764a14bc5856f0b0bb3068533... <https://github.com/crash-utility/crash/commit/48764a14bc5856f0b0bb3068533...