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    Subject[PATCH 4.11 129/197] powerpc/64e: Fix hang when debugging programs with relocated kernel
    Date
    4.11-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: LiuHailong <liu.hailong6@zte.com.cn>

    commit fd615f69a18a9d4aa5ef02a1dc83f319f75da8e7 upstream.

    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: Liu Hailong <liu.hailong6@zte.com.cn>
    Signed-off-by: Jiang Xuexin <jiang.xuexin@zte.com.cn>
    Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
    Reviewed-by: Liu Song <liu.song11@zte.com.cn>
    Reviewed-by: Huang 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: 1cb6e0649248 ("powerpc/book3e: support CONFIG_RELOCATABLE")
    Signed-off-by: Scott Wood <oss@buserror.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/kernel/exceptions-64e.S | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    --- a/arch/powerpc/kernel/exceptions-64e.S
    +++ b/arch/powerpc/kernel/exceptions-64e.S
    @@ -735,8 +735,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
    andis. r15,r14,(DBSR_IC|DBSR_BT)@h
    beq+ 1f

    +#ifdef CONFIG_RELOCATABLE
    + ld r15,PACATOC(r13)
    + ld r14,interrupt_base_book3e@got(r15)
    + ld r15,__end_interrupts@got(r15)
    +#else
    LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
    LOAD_REG_IMMEDIATE(r15,__end_interrupts)
    +#endif
    cmpld cr0,r10,r14
    cmpld cr1,r10,r15
    blt+ cr0,1f
    @@ -799,8 +805,14 @@ kernel_dbg_exc:
    andis. r15,r14,(DBSR_IC|DBSR_BT)@h
    beq+ 1f

    +#ifdef CONFIG_RELOCATABLE
    + ld r15,PACATOC(r13)
    + ld r14,interrupt_base_book3e@got(r15)
    + ld r15,__end_interrupts@got(r15)
    +#else
    LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
    LOAD_REG_IMMEDIATE(r15,__end_interrupts)
    +#endif
    cmpld cr0,r10,r14
    cmpld cr1,r10,r15
    blt+ cr0,1f

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