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    powerpc/64e: Fix hang when debugging programs with relocated kernel · fd615f69
    LiuHailong authored
    
    
    Debug interrupts can be taken during interrupt entry, since interrupt
    entry does not automatically turn them off.  The kernel will check
    whether the faulting instruction is between [interrupt_base_book3e,
    __end_interrupts], and if so clear MSR[DE] and return.
    
    However, when the kernel is built with CONFIG_RELOCATABLE, it can't use
    LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e) and
    LOAD_REG_IMMEDIATE(r15,__end_interrupts), as they ignore relocation.
    Thus, if the kernel is actually running at a different address than it
    was built at, the address comparison will fail, and the exception entry
    code will hang at kernel_dbg_exc.
    
    r2(toc) is also not usable here, as r2 still holds data from the
    interrupted context, so LOAD_REG_ADDR() doesn't work either.  So we use
    the *name@got* to get the EV of two labels directly.
    
    Test programs test.c shows as follows:
    int main(int argc, char *argv[])
    {
    	if (access("/proc/sys/kernel/perf_event_paranoid", F_OK) == -1)
    		printf("Kernel doesn't have perf_event support\n");
    }
    
    Steps to reproduce the bug, for example:
     1) ./gdb ./test
     2) (gdb) b access
     3) (gdb) r
     4) (gdb) s
    
    Signed-off-by: default avatarLiu Hailong <liu.hailong6@zte.com.cn>
    Signed-off-by: default avatarJiang Xuexin <jiang.xuexin@zte.com.cn>
    Reviewed-by: default avatarJiang Biao <jiang.biao2@zte.com.cn>
    Reviewed-by: default avatarLiu Song <liu.song11@zte.com.cn>
    Reviewed-by: default avatarHuang Jian <huang.jian@zte.com.cn>
    [scottwood: cleaned up commit message, and specified bad behavior
     as a hang rather than an oops to correspond to mainline kernel behavior]
    Fixes: 1cb6e064
    
     ("powerpc/book3e: support CONFIG_RELOCATABLE")
    Cc: <stable@vger.kernel.org> # 4.4.x-
    Signed-off-by: default avatarScott Wood <oss@buserror.net>
    fd615f69