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On x86-32, Tetsuo Handa and Fengguang Wu reported unwinder warnings like: WARNING: kernel stack regs at f60bb9c8 in swapper:1 has bad 'bp' value 0ba00000 And also there were some stack dumps with a bunch of unreliable '?' symbols after an apic_timer_interrupt symbol, meaning the unwinder got confused when it tried to read the regs. The cause of those issues is that, with GCC 4.8 (and possibly older), there are cases where GCC misaligns the stack pointer in a leaf function for no apparent reason: c124a388 <acpi_rs_move_data>: c124a388: 55 push %ebp c124a389: 89 e5 mov %esp,%ebp c124a38b: 57 push %edi c124a38c: 56 push %esi c124a38d: 89 d6 mov %edx,%esi c124a38f: 53 push %ebx c124a390: 31 db xor %ebx,%ebx c124a392: 83 ec 03 sub $0x3,%esp ... c124a3e3: 83 c4 03 add $0x3,%esp c124a3e6: 5b pop %ebx c124a3e7: 5e pop %esi c124a3e8: 5f pop %edi c124a3e9: 5d pop %ebp c124a3ea: c3 ret If an interrupt occurs in such a function, the regs on the stack will be unaligned, which breaks the frame pointer encoding assumption. So on 32-bit, use the MSB instead of the LSB to encode the regs. This isn't an issue on 64-bit, because interrupts align the stack before writing to it. Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Byungchul Park <byungchul.park@lge.com> Cc: LKP <lkp@01.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/279a26996a482ca716605c7dbc7f2db9d8d91e81.1507597785.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.