• Anton Blanchard's avatar
    powerpc/perf: Fix ABIv2 kernel backtraces · 85101af1
    Anton Blanchard authored
    ABIv2 kernels are failing to backtrace through the kernel. An example:
    
    39.30%  readseek2_proce  [kernel.kallsyms]    [k] find_get_entry
                |
                --- find_get_entry
                   __GI___libc_read
    
    The problem is in valid_next_sp() where we check that the new stack
    pointer is at least STACK_FRAME_OVERHEAD below the previous one.
    
    ABIv1 has a minimum stack frame size of 112 bytes consisting of 48 bytes
    and 64 bytes of parameter save area. ABIv2 changes that to 32 bytes
    with no paramter save area.
    
    STACK_FRAME_OVERHEAD is in theory the minimum stack frame size,
    but we over 240 uses of it, some of which assume that it includes
    space for the parameter area.
    
    We need to work through all our stack defines and rationalise them
    but let's fix perf now by creating STACK_FRAME_MIN_SIZE and using
    in valid_next_sp(). This fixes the issue:
    
    30.64%  readseek2_proce  [kernel.kallsyms]    [k] find_get_entry
                |
                --- find_get_entry
                   pagecache_get_page
                   generic_file_read_iter
                   new_sync_read
                   vfs_read
                   sys_read
                   syscall_exit
                   __GI___libc_read
    
    Cc: stable@vger.kernel.org # 3.16+
    Reported-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
    85101af1
ptrace.h 7.16 KB