Query: ARM64: Behavior of el1_dbg exception while executing el0_dbg
panand at redhat.com
Fri Jan 16 04:00:09 PST 2015
On Thursday 15 January 2015 10:17 PM, Pratyush Anand wrote:
> Hi Will / Catalin,
> On Tuesday 13 January 2015 11:23 PM, Pratyush Anand wrote:
>> I will still try to find some way to capture enable_dbg macro path.H
> I did instrumented debug tap points at all the location from where
> enable_debug macro is called(see attached debug patch). But, I do not
> see that, execution reaches to any of those tap points between el0_dbg
> and el1_dbg, and tap points debug log also confirms that el1_dbg is
> raised before el0_dbg is returned.
Probably we all missed this, ARMv8 specs is very clear about it. In
section "D2.1 About debug exceptions" it says:
Software Breakpoint Instruction exceptions cannot be masked. The PE
takes Software Breakpoint Instruction exceptions regardless of both of
• The current Exception level.
• The current Security state.
So, reception of el1_dbg while executing el0_dbg seems perfectly normal
to me. If you agree then I am back with the original query which I asked
in the beginning of the
ie how can instruction_pointer be wrong when second el1_dbg is called
-> el0_dbg (After executing BRK instruction by user)
 -> el1_dbg (when uprobe break handler at  executes BRK instruction)
(At the end of this ELR_EL1 is programmed with fffffdfffc000004)
 -> el1_dbg (when kprobe break handler at  enables single stepping)
(Here ELR_EL1 was found fffffe0000092470).So When this el1_dbg was
received, then regs->pc values are not same what was programmed in
ELR_EL1 at the return of .
More information about the linux-arm-kernel