On Tue, Nov 06, 2018 at 03:19:35PM +0800, Zhaoyang Huang wrote: > From: Zhaoyang Huang <[email protected]> > > In some cases, the instruction of "bl foo1" will be the last one of the > foo2[1], which will cause the lr be the first instruction of the adjacent > foo3[2]. Hence, the backtrace will show the weird result as bellow[3]. > The patch will fix it by miner 4 of the lr when dump_backtrace
This has come up in the past (and a similar patch has been applied, then reverted). In general, we don't know that a function call was made via BL, and therefore cannot know that LR - 4 is the address of the caller. The caller could set up the LR as it likes, then B or BR to the callee, and depending on how the basic blocks get laid out in memory, LR - 4 might point at something completely different. More ideally, the compiler wouldn't end a function with a BL. When does that happen, and is there some way we could arrange for that to not happen? e.g. somehow pad a NOP after the BL. Thanks, Mark. > > [1] > 0xffffff80081e6b04 <handle_mm_fault+3996>: adrp x0, 0xffffff8008ca8000 > 0xffffff80081e6b08 <handle_mm_fault+4000>: add x0, x0, #0x5a8 > 0xffffff80081e6b0c <handle_mm_fault+4004>: bl 0xffffff80081b0ca0 > <panic> > 0xffffff80081e6b10 <access_remote_vm>: stp x29, x30, [sp,#-64]! > 0xffffff80081e6b14 <access_remote_vm+4>: mov x29, sp > > [2] > crash_arm64> rd ffffffc02eec3bd0 2 > ffffffc02eec3bd0: ffffffc02eec3cb0 ffffff80081e6b10 > > [3] > wrong: > [<ffffff80081b0d90>] panic+0xf0/0x24c > [<ffffff80081e6b10>] access_remote_vm+0x0/0x5c > [<ffffff800809d7b0>] do_page_fault+0x290/0x3b8 > [<ffffff8008081570>] do_mem_abort+0x64/0xdc > > correct: > [ffffffc02eec3bd0] panic at ffffff80081b0da4 > [ffffffc02eec3cb0] handle_mm_fault at ffffff80081e6b0c > [ffffffc02eec3d80] do_page_fault at ffffff800809d7ac > [ffffffc02eec3df0] do_mem_abort at ffffff800808156c > > Signed-off-by: Zhaoyang Huang <[email protected]> > --- > arch/arm64/kernel/traps.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index d399d45..7a097cc 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -113,7 +113,7 @@ void dump_backtrace(struct pt_regs *regs, struct > task_struct *tsk) > > if (tsk == current) { > frame.fp = (unsigned long)__builtin_frame_address(0); > - frame.pc = (unsigned long)dump_backtrace; > + frame.pc = (unsigned long)dump_backtrace + 4; > } else { > /* > * task blocked in __switch_to > @@ -130,7 +130,7 @@ void dump_backtrace(struct pt_regs *regs, struct > task_struct *tsk) > do { > /* skip until specified stack frame */ > if (!skip) { > - dump_backtrace_entry(frame.pc); > + dump_backtrace_entry(frame.pc - 4); > } else if (frame.fp == regs->regs[29]) { > skip = 0; > /* > -- > 1.9.1 >
