From fd615f69a18a9d4aa5ef02a1dc83f319f75da8e7 Mon Sep 17 00:00:00 2001 From: LiuHailong Date: Tue, 7 Feb 2017 10:35:52 +0800 Subject: [PATCH] powerpc/64e: Fix hang when debugging programs with relocated kernel 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 Signed-off-by: Jiang Xuexin Reviewed-by: Jiang Biao Reviewed-by: Liu Song Reviewed-by: Huang Jian [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") Cc: # 4.4.x- Signed-off-by: Scott Wood --- arch/powerpc/kernel/exceptions-64e.S | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S index 45b453e4d0c8..acd8ca76233e 100644 --- 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