• Thomas Gleixner's avatar
    x86: Prevent GCC 4.4.x (pentium-mmx et al) function prologue wreckage · 746357d6
    Thomas Gleixner authored
    When the kernel is compiled with -pg for tracing GCC 4.4.x inserts
    stack alignment of a function _before_ the mcount prologue if the
    -march=pentium-mmx is set and -mtune=generic is not set. This breaks
    the assumption of the function graph tracer which expects that the
    mcount prologue
    
           push %ebp
           mov  %esp, %ebp
    
    is the first stack operation in a function because it needs to modify
    the function return address on the stack to trap into the tracer
    before returning to the real caller.
    
    The generated code is:
    
            push   %edi
            lea    0x8(%esp),%edi
            and    $0xfffffff0,%esp
            pushl  -0x4(%edi)
            push   %ebp
            mov    %esp,%ebp
    
    so the tracer modifies the copy of the return address which is stored
    after the stack alignment and therefor does not trap the return which
    in turn breaks the call chain logic of the tracer and leads to a
    kernel panic.
    
    Aside of the fact that the generated code is horrible for no good
    reason other -march -mtune options generate the expected:
    
            push   %ebp
            mov    %esp,%ebp
            and    $0xfffffff0,%esp
    
    which does the same and keeps everything intact.
    
    After some experimenting we found out that this problem is restricted
    to gcc4.4.x and to the following -march settings:
    
    i586, pentium, pentium-mmx, k6, k6-2, k6-3, winchip-c6, winchip2, c3,
    geode
    
    By adding -mtune=generic the code generator produces always the
    expected code.
    
    So forcing -mtune=generic when CONFIG_FUNCTION_GRAPH_TRACER=y is not
    pretty, but at the moment the only way to prevent that the kernel
    trips over gcc-shrooms induced code madness.
    
    Most distro kernels have CONFIG_X86_GENERIC=y anyway which forces
    -mtune=generic as well so it will not impact those.
    
    References: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109
    	    http://lkml.org/lkml/2009/11/19/17Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    LKML-Reference: <alpine.LFD.2.00.0911200206570.24119@localhost.localdomain>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>,
    Cc: Jeff Law <law@redhat.com>
    Cc: gcc@gcc.gnu.org
    Cc: David Daney <ddaney@caviumnetworks.com>
    Cc: Andrew Haley <aph@redhat.com>
    Cc: Richard Guenther <richard.guenther@gmail.com>
    Cc: stable@kernel.org
    746357d6
Makefile_32.cpu 2.73 KB