• Jungseok Lee's avatar
    arm64: Synchronise dump_backtrace() with perf callchain · 9f93f3e9
    Jungseok Lee authored
    
    
    Unlike perf callchain relying on walk_stackframe(), dump_backtrace()
    has its own backtrace logic. A major difference between them is the
    moment a symbol is recorded. Perf writes down a symbol *before*
    calling unwind_frame(), but dump_backtrace() prints it out *after*
    unwind_frame(). As a result, the last valid symbol cannot be hooked
    in case of dump_backtrace(). This patch addresses the issue as
    synchronising dump_backtrace() with perf callchain.
    
    A simple test and its results are as follows:
    
    - crash trigger
    
     $ sudo echo c > /proc/sysrq-trigger
    
    - current status
    
     Call trace:
     [<fffffe00003dc738>] sysrq_handle_crash+0x24/0x30
     [<fffffe00003dd2ac>] __handle_sysrq+0x128/0x19c
     [<fffffe00003dd730>] write_sysrq_trigger+0x60/0x74
     [<fffffe0000249fc4>] proc_reg_write+0x84/0xc0
     [<fffffe00001f2638>] __vfs_write+0x44/0x104
     [<fffffe00001f2e60>] vfs_write+0x98/0x1a8
     [<fffffe00001f3730>] SyS_write+0x50/0xb0
    
    - with this change
    
     Call trace:
     [<fffffe00003dc738>] sysrq_handle_crash+0x24/0x30
     [<fffffe00003dd2ac>] __handle_sysrq+0x128/0x19c
     [<fffffe00003dd730>] write_sysrq_trigger+0x60/0x74
     [<fffffe0000249fc4>] proc_reg_write+0x84/0xc0
     [<fffffe00001f2638>] __vfs_write+0x44/0x104
     [<fffffe00001f2e60>] vfs_write+0x98/0x1a8
     [<fffffe00001f3730>] SyS_write+0x50/0xb0
     [<fffffe00000939ec>] el0_svc_naked+0x20/0x28
    
    Note that this patch does not cover a case where MMU is disabled. The
    last stack frame of swapper, for example, has PC in a form of physical
    address. Unfortunately, a simple conversion using phys_to_virt() cannot
    cover all scenarios since PC is retrieved from LR - 4, not LR. It is
    a big tradeoff to change both head.S and unwind_frame() for only a few
    of symbols in *.S. Thus, this hunk does not take care of the case.
    
    Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
    Cc: James Morse <james.morse@arm.com>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Signed-off-by: default avatarJungseok Lee <jungseoklee85@gmail.com>
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    9f93f3e9
traps.c 13.2 KB