* [PATCH 21/31] Add debugger entry points for MIPS
@ 2016-01-28 19:47 Jeffrey Merkey
2016-01-28 21:41 ` kbuild test robot
2016-02-01 12:26 ` Maciej W. Rozycki
0 siblings, 2 replies; 5+ messages in thread
From: Jeffrey Merkey @ 2016-01-28 19:47 UTC (permalink / raw)
To: linux-kernel; +Cc: ralf, james.hogan, linux.mdb, linux-mips
This patch series adds an export which can be set by system debuggers to
direct the hard lockup and soft lockup detector to trigger a breakpoint
exception and enter a debugger if one is active. It is assumed that if
someone sets this variable, then an breakpoint handler of some sort will
be actively loaded or registered via the notify die handler chain.
This addition is extremely useful for debugging hard and soft lockups
real time and quickly from a console debugger.
Signed-off-by: Jeffrey Merkey <jeffmerkey@gmail.com>
---
arch/mips/include/asm/kdebug.h | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/arch/mips/include/asm/kdebug.h b/arch/mips/include/asm/kdebug.h
index 8e3d08e..af5999e 100644
--- a/arch/mips/include/asm/kdebug.h
+++ b/arch/mips/include/asm/kdebug.h
@@ -16,4 +16,16 @@ enum die_val {
DIE_UPROBE_XOL,
};
+
+void arch_breakpoint(void)
+{
+ __asm__ __volatile__(
+ ".globl breakinst\n\t"
+ ".set\tnoreorder\n\t"
+ "nop\n"
+ "breakinst:\tbreak\n\t"
+ "nop\n\t"
+ ".set\treorder");
+}
+
#endif /* _ASM_MIPS_KDEBUG_H */
--
1.8.3.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 21/31] Add debugger entry points for MIPS
2016-01-28 19:47 [PATCH 21/31] Add debugger entry points for MIPS Jeffrey Merkey
@ 2016-01-28 21:41 ` kbuild test robot
2016-02-01 12:26 ` Maciej W. Rozycki
1 sibling, 0 replies; 5+ messages in thread
From: kbuild test robot @ 2016-01-28 21:41 UTC (permalink / raw)
To: Jeffrey Merkey
Cc: kbuild-all, linux-kernel, ralf, james.hogan, linux.mdb, linux-mips
[-- Attachment #1: Type: text/plain, Size: 2270 bytes --]
Hi Jeffrey,
[auto build test ERROR on v4.5-rc1]
[also build test ERROR on next-20160128]
[cannot apply to tip/x86/core]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
url: https://github.com/0day-ci/linux/commits/Jeffrey-Merkey/Add-hard-soft-lockup-debugger-entry-points/20160129-035852
config: mips-jz4740 (attached as .config)
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=mips
All errors (new ones prefixed by >>):
kernel/sys.o: In function `arch_breakpoint':
>> sys.c:(.text+0x880): multiple definition of `arch_breakpoint'
kernel/sysctl.o:sysctl.c:(.text+0x134c): first defined here
kernel/sys.o: In function `arch_breakpoint':
>> sys.c:(.text+0x884): multiple definition of `breakinst'
kernel/sysctl.o:sysctl.c:(.text+0x1350): first defined here
kernel/notifier.o: In function `arch_breakpoint':
notifier.c:(.text+0x678): multiple definition of `arch_breakpoint'
kernel/sysctl.o:sysctl.c:(.text+0x134c): first defined here
kernel/notifier.o: In function `arch_breakpoint':
notifier.c:(.text+0x67c): multiple definition of `breakinst'
kernel/sysctl.o:sysctl.c:(.text+0x1350): first defined here
kernel/sched/built-in.o: In function `arch_breakpoint':
(.text+0x3b0): multiple definition of `arch_breakpoint'
kernel/sysctl.o:sysctl.c:(.text+0x134c): first defined here
kernel/sched/built-in.o: In function `arch_breakpoint':
(.text+0x3b4): multiple definition of `breakinst'
kernel/sysctl.o:sysctl.c:(.text+0x1350): first defined here
kernel/kprobes.o: In function `arch_breakpoint':
kprobes.c:(.text+0x1690): multiple definition of `arch_breakpoint'
kernel/sysctl.o:sysctl.c:(.text+0x134c): first defined here
kernel/kprobes.o: In function `arch_breakpoint':
kprobes.c:(.text+0x1694): multiple definition of `breakinst'
kernel/sysctl.o:sysctl.c:(.text+0x1350): first defined here
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 18092 bytes --]
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 21/31] Add debugger entry points for MIPS
2016-01-28 19:47 [PATCH 21/31] Add debugger entry points for MIPS Jeffrey Merkey
2016-01-28 21:41 ` kbuild test robot
@ 2016-02-01 12:26 ` Maciej W. Rozycki
2016-02-01 16:03 ` Jeff Merkey
1 sibling, 1 reply; 5+ messages in thread
From: Maciej W. Rozycki @ 2016-02-01 12:26 UTC (permalink / raw)
To: Jeffrey Merkey
Cc: linux-kernel, Ralf Baechle, James Hogan, linux.mdb, linux-mips
On Thu, 28 Jan 2016, Jeffrey Merkey wrote:
> This patch series adds an export which can be set by system debuggers to
> direct the hard lockup and soft lockup detector to trigger a breakpoint
> exception and enter a debugger if one is active. It is assumed that if
> someone sets this variable, then an breakpoint handler of some sort will
> be actively loaded or registered via the notify die handler chain.
>
> This addition is extremely useful for debugging hard and soft lockups
> real time and quickly from a console debugger.
What's the intended use case for this hook and what do you call a console
debugger?
I'm asking because from the debugging perspective the Linux kernel is a
bare metal application and for such the BREAK instruction is not the usual
choice on the MIPS target. This instruction is normally used for userland
debugging, it traps to the kernel and is handled there. Furthermore there
are a few other applications of this instruction defined as a part of the
MIPS ABI, also handled by the kernel, determined by the breakpoint code
embedded with the instruction word, e.g. to trap integer division errors.
See arch/mips/include/uapi/asm/break.h for the codes defined so far.
All this means the trap may not be appropriate for debugging the kernel
itself as you don't want to intercept it or the system won't run
correctly. You'd have to hook into the kernel itself to intercept it too.
But if you do have a working debug environment already set up around this
arrangement, then it might be fine after all. In that case I think using
a non-zero breakpoint code would make sense though, as 0 is often treated
as a random (spurious) trap (it was used by IRIX though). Or do you
detect it by the symbol name somehow?
I've got a couple of further notes on the patch itself below.
> diff --git a/arch/mips/include/asm/kdebug.h b/arch/mips/include/asm/kdebug.h
> index 8e3d08e..af5999e 100644
> --- a/arch/mips/include/asm/kdebug.h
> +++ b/arch/mips/include/asm/kdebug.h
> @@ -16,4 +16,16 @@ enum die_val {
> DIE_UPROBE_XOL,
> };
>
> +
> +void arch_breakpoint(void)
> +{
> + __asm__ __volatile__(
> + ".globl breakinst\n\t"
Please keep formatting consistent -- the rest of code below uses `\t' as
the separator, so use it here as well. We don't have an established
inline assembly formatting style, so please just keep your chosen one
consistent.
> + ".set\tnoreorder\n\t"
> + "nop\n"
> + "breakinst:\tbreak\n\t"
> + "nop\n\t"
> + ".set\treorder");
> +}
> +
> #endif /* _ASM_MIPS_KDEBUG_H */
Why do you need these NOPs around the breakpoint? You also need to mark
`breakinst' as a function symbol (`.aent' might do) or otherwise you'll
get garbled disassembly if this is built as microMIPS code.
Maciej
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 21/31] Add debugger entry points for MIPS
2016-02-01 12:26 ` Maciej W. Rozycki
@ 2016-02-01 16:03 ` Jeff Merkey
2016-02-01 21:25 ` Ralf Baechle
0 siblings, 1 reply; 5+ messages in thread
From: Jeff Merkey @ 2016-02-01 16:03 UTC (permalink / raw)
To: Maciej W. Rozycki
Cc: Jeffrey Merkey, linux-kernel, Ralf Baechle, James Hogan, linux-mips
On 2/1/16, Maciej W. Rozycki <macro@imgtec.com> wrote:
> On Thu, 28 Jan 2016, Jeffrey Merkey wrote:
>
>> This patch series adds an export which can be set by system debuggers to
>> direct the hard lockup and soft lockup detector to trigger a breakpoint
>> exception and enter a debugger if one is active. It is assumed that if
>> someone sets this variable, then an breakpoint handler of some sort will
>> be actively loaded or registered via the notify die handler chain.
>>
>> This addition is extremely useful for debugging hard and soft lockups
>> real time and quickly from a console debugger.
>
> What's the intended use case for this hook and what do you call a console
> debugger?
>
> I'm asking because from the debugging perspective the Linux kernel is a
> bare metal application and for such the BREAK instruction is not the usual
> choice on the MIPS target. This instruction is normally used for userland
> debugging, it traps to the kernel and is handled there. Furthermore there
> are a few other applications of this instruction defined as a part of the
> MIPS ABI, also handled by the kernel, determined by the breakpoint code
> embedded with the instruction word, e.g. to trap integer division errors.
> See arch/mips/include/uapi/asm/break.h for the codes defined so far.
>
> All this means the trap may not be appropriate for debugging the kernel
> itself as you don't want to intercept it or the system won't run
> correctly. You'd have to hook into the kernel itself to intercept it too.
>
> But if you do have a working debug environment already set up around this
> arrangement, then it might be fine after all. In that case I think using
> a non-zero breakpoint code would make sense though, as 0 is often treated
> as a random (spurious) trap (it was used by IRIX though). Or do you
> detect it by the symbol name somehow?
>
> I've got a couple of further notes on the patch itself below.
>
>> diff --git a/arch/mips/include/asm/kdebug.h
>> b/arch/mips/include/asm/kdebug.h
>> index 8e3d08e..af5999e 100644
>> --- a/arch/mips/include/asm/kdebug.h
>> +++ b/arch/mips/include/asm/kdebug.h
>> @@ -16,4 +16,16 @@ enum die_val {
>> DIE_UPROBE_XOL,
>> };
>>
>> +
>> +void arch_breakpoint(void)
>> +{
>> + __asm__ __volatile__(
>> + ".globl breakinst\n\t"
>
> Please keep formatting consistent -- the rest of code below uses `\t' as
> the separator, so use it here as well. We don't have an established
> inline assembly formatting style, so please just keep your chosen one
> consistent.
>
>> + ".set\tnoreorder\n\t"
>> + "nop\n"
>> + "breakinst:\tbreak\n\t"
>> + "nop\n\t"
>> + ".set\treorder");
>> +}
>> +
>> #endif /* _ASM_MIPS_KDEBUG_H */
>
> Why do you need these NOPs around the breakpoint? You also need to mark
> `breakinst' as a function symbol (`.aent' might do) or otherwise you'll
> get garbled disassembly if this is built as microMIPS code.
>
> Maciej
>
You can drop this patch series, I am rethinking a better way to do this.
Jeff
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 21/31] Add debugger entry points for MIPS
2016-02-01 16:03 ` Jeff Merkey
@ 2016-02-01 21:25 ` Ralf Baechle
0 siblings, 0 replies; 5+ messages in thread
From: Ralf Baechle @ 2016-02-01 21:25 UTC (permalink / raw)
To: Jeff Merkey
Cc: Maciej W. Rozycki, Jeffrey Merkey, linux-kernel, James Hogan, linux-mips
On Mon, Feb 01, 2016 at 09:03:54AM -0700, Jeff Merkey wrote:
> You can drop this patch series, I am rethinking a better way to do this.
Dropped.
Ralf
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-01-28 19:47 [PATCH 21/31] Add debugger entry points for MIPS Jeffrey Merkey
2016-01-28 21:41 ` kbuild test robot
2016-02-01 12:26 ` Maciej W. Rozycki
2016-02-01 16:03 ` Jeff Merkey
2016-02-01 21:25 ` Ralf Baechle
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