When fall-through warnings was enabled by default, commit d93512ef0f0e
("Makefile: Globally enable fall-through warning"), the following
warnings was starting to show up:
../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
through [-Wimplicit-fallthrough=]
if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
^
../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
case 2:
^~~~
../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
through [-Wimplicit-fallthrough=]
if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
^
../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
default:
^~~~~~~
Rework so that the compiler doesn't warn about fall-through. Rework so
the code looks like the arm code. Since the comment in the function
indicates taht this is supposed to behave the same way as arm32 because
it handles 32-bit tasks also.
Cc: [email protected] # v3.16+
Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
Signed-off-by: Anders Roxell <[email protected]>
---
arch/arm64/kernel/hw_breakpoint.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index dceb84520948..ea616adf1cf1 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -535,14 +535,17 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
case 0:
/* Aligned */
break;
- case 1:
- /* Allow single byte watchpoint. */
- if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
- break;
case 2:
/* Allow halfword watchpoints and breakpoints. */
if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
break;
+ /* Fall through */
+ case 1:
+ case 3:
+ /* Allow single byte watchpoint. */
+ if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
+ break;
+ /* Fall through */
default:
return -EINVAL;
}
--
2.20.1
On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote:
> When fall-through warnings was enabled by default, commit d93512ef0f0e
> ("Makefile: Globally enable fall-through warning"), the following
> warnings was starting to show up:
>
> ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
> ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
> through [-Wimplicit-fallthrough=]
> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> ^
> ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
> case 2:
> ^~~~
> ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
> through [-Wimplicit-fallthrough=]
> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> ^
> ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
> default:
> ^~~~~~~
>
> Rework so that the compiler doesn't warn about fall-through. Rework so
> the code looks like the arm code. Since the comment in the function
> indicates taht this is supposed to behave the same way as arm32 because
Typo: s/taht/that/
> it handles 32-bit tasks also.
>
> Cc: [email protected] # v3.16+
> Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
> Signed-off-by: Anders Roxell <[email protected]>
The patch itself looks fine, but I don't think this needs a CC to
stable, nor does it require that fixes tag, as there's no functional
problem.
If anything, it fixes:
d93512ef0f0e (" Makefile: Globally enable fall-through warning")
... given the commit message for that patch states:
Now that all the fall-through warnings have been addressed in the
kernel, enable the fall-through warning globally.
... and the existence of this patch implies otherwise.
IIUC that patch isn't even in mainline yet, but given this is simple I
imagine that Will and Catalin might be happy to pick this up for the
next rc.
Thanks,
Mark.
> ---
> arch/arm64/kernel/hw_breakpoint.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> index dceb84520948..ea616adf1cf1 100644
> --- a/arch/arm64/kernel/hw_breakpoint.c
> +++ b/arch/arm64/kernel/hw_breakpoint.c
> @@ -535,14 +535,17 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
> case 0:
> /* Aligned */
> break;
> - case 1:
> - /* Allow single byte watchpoint. */
> - if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> - break;
> case 2:
> /* Allow halfword watchpoints and breakpoints. */
> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> break;
> + /* Fall through */
> + case 1:
> + case 3:
> + /* Allow single byte watchpoint. */
> + if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> + break;
> + /* Fall through */
> default:
> return -EINVAL;
> }
> --
> 2.20.1
>
On Fri, Jul 26, 2019 at 01:10:57PM +0100, Mark Rutland wrote:
> On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote:
> > When fall-through warnings was enabled by default, commit d93512ef0f0e
> > ("Makefile: Globally enable fall-through warning"), the following
> > warnings was starting to show up:
> >
> > ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
> > ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
> > through [-Wimplicit-fallthrough=]
> > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> > ^
> > ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
> > case 2:
> > ^~~~
> > ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
> > through [-Wimplicit-fallthrough=]
> > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> > ^
> > ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
> > default:
> > ^~~~~~~
> >
> > Rework so that the compiler doesn't warn about fall-through. Rework so
> > the code looks like the arm code. Since the comment in the function
> > indicates taht this is supposed to behave the same way as arm32 because
>
> Typo: s/taht/that/
>
> > it handles 32-bit tasks also.
> >
> > Cc: [email protected] # v3.16+
> > Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
> > Signed-off-by: Anders Roxell <[email protected]>
>
> The patch itself looks fine, but I don't think this needs a CC to
> stable, nor does it require that fixes tag, as there's no functional
> problem.
Hmm... I now see I spoke too soon, and this is making the 1-byte
breakpoint work at a 3-byte offset.
Given that:
Acked-by: Mark Rutland <[email protected]>
... and the fixes and stable tags are appropriate for that portion of
the patch.
Sorry for the noise.
Thanks,
Mark.
> > ---
> > arch/arm64/kernel/hw_breakpoint.c | 11 +++++++----
> > 1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> > index dceb84520948..ea616adf1cf1 100644
> > --- a/arch/arm64/kernel/hw_breakpoint.c
> > +++ b/arch/arm64/kernel/hw_breakpoint.c
> > @@ -535,14 +535,17 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
> > case 0:
> > /* Aligned */
> > break;
> > - case 1:
> > - /* Allow single byte watchpoint. */
> > - if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> > - break;
> > case 2:
> > /* Allow halfword watchpoints and breakpoints. */
> > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> > break;
> > + /* Fall through */
> > + case 1:
> > + case 3:
> > + /* Allow single byte watchpoint. */
> > + if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> > + break;
> > + /* Fall through */
> > default:
> > return -EINVAL;
> > }
> > --
> > 2.20.1
> >
On 26/07/2019 13:27, Will Deacon wrote:
> On Fri, Jul 26, 2019 at 01:13:54PM +0100, Mark Rutland wrote:
>> On Fri, Jul 26, 2019 at 01:10:57PM +0100, Mark Rutland wrote:
>>> On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote:
>>>> When fall-through warnings was enabled by default, commit d93512ef0f0e
>>>> ("Makefile: Globally enable fall-through warning"), the following
>>>> warnings was starting to show up:
>>>>
>>>> ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
>>>> ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
>>>> through [-Wimplicit-fallthrough=]
>>>> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
>>>> ^
>>>> ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
>>>> case 2:
>>>> ^~~~
>>>> ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
>>>> through [-Wimplicit-fallthrough=]
>>>> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
>>>> ^
>>>> ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
>>>> default:
>>>> ^~~~~~~
>>>>
>>>> Rework so that the compiler doesn't warn about fall-through. Rework so
>>>> the code looks like the arm code. Since the comment in the function
>>>> indicates taht this is supposed to behave the same way as arm32 because
>>>
>>> Typo: s/taht/that/
>>>
>>>> it handles 32-bit tasks also.
>>>>
>>>> Cc: [email protected] # v3.16+
>>>> Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
>>>> Signed-off-by: Anders Roxell <[email protected]>
>>>
>>> The patch itself looks fine, but I don't think this needs a CC to
>>> stable, nor does it require that fixes tag, as there's no functional
>>> problem.
>>
>> Hmm... I now see I spoke too soon, and this is making the 1-byte
>> breakpoint work at a 3-byte offset.
>
> I still don't think it's quite right though, since it forbids a 2-byte
> watchpoint on a byte-aligned address.
Plus, AFAICS, a 1-byte watchpoint on a 2-byte-aligned address.
Not that I know anything about this code, but it does start to look like
it might want rewriting without the offending switch statement anyway.
At a glance, it looks like the intended semantic might boil down to:
if (hw->ctrl.len > offset)
return -EINVAL;
Robin.
> I think the arm64 code matches what we had on 32-bit prior to
> d968d2b801d8 ("ARM: 7497/1: hw_breakpoint: allow single-byte watchpoints
> on all addresses"), so we should have one patch bringing us up to speed
> with that change, and then another annotating the fallthroughs.
>
> Will
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
On Fri, Jul 26, 2019 at 01:13:54PM +0100, Mark Rutland wrote:
> On Fri, Jul 26, 2019 at 01:10:57PM +0100, Mark Rutland wrote:
> > On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote:
> > > When fall-through warnings was enabled by default, commit d93512ef0f0e
> > > ("Makefile: Globally enable fall-through warning"), the following
> > > warnings was starting to show up:
> > >
> > > ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
> > > ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
> > > through [-Wimplicit-fallthrough=]
> > > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> > > ^
> > > ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
> > > case 2:
> > > ^~~~
> > > ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
> > > through [-Wimplicit-fallthrough=]
> > > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> > > ^
> > > ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
> > > default:
> > > ^~~~~~~
> > >
> > > Rework so that the compiler doesn't warn about fall-through. Rework so
> > > the code looks like the arm code. Since the comment in the function
> > > indicates taht this is supposed to behave the same way as arm32 because
> >
> > Typo: s/taht/that/
> >
> > > it handles 32-bit tasks also.
> > >
> > > Cc: [email protected] # v3.16+
> > > Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
> > > Signed-off-by: Anders Roxell <[email protected]>
> >
> > The patch itself looks fine, but I don't think this needs a CC to
> > stable, nor does it require that fixes tag, as there's no functional
> > problem.
>
> Hmm... I now see I spoke too soon, and this is making the 1-byte
> breakpoint work at a 3-byte offset.
I still don't think it's quite right though, since it forbids a 2-byte
watchpoint on a byte-aligned address.
I think the arm64 code matches what we had on 32-bit prior to
d968d2b801d8 ("ARM: 7497/1: hw_breakpoint: allow single-byte watchpoints
on all addresses"), so we should have one patch bringing us up to speed
with that change, and then another annotating the fallthroughs.
Will
On Fri, Jul 26, 2019 at 01:38:24PM +0100, Robin Murphy wrote:
> On 26/07/2019 13:27, Will Deacon wrote:
> > On Fri, Jul 26, 2019 at 01:13:54PM +0100, Mark Rutland wrote:
> > > On Fri, Jul 26, 2019 at 01:10:57PM +0100, Mark Rutland wrote:
> > > > On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote:
> > > > > When fall-through warnings was enabled by default, commit d93512ef0f0e
> > > > > ("Makefile: Globally enable fall-through warning"), the following
> > > > > warnings was starting to show up:
> > > > >
> > > > > ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
> > > > > ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
> > > > > through [-Wimplicit-fallthrough=]
> > > > > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
> > > > > ^
> > > > > ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
> > > > > case 2:
> > > > > ^~~~
> > > > > ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
> > > > > through [-Wimplicit-fallthrough=]
> > > > > if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
> > > > > ^
> > > > > ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
> > > > > default:
> > > > > ^~~~~~~
> > > > >
> > > > > Rework so that the compiler doesn't warn about fall-through. Rework so
> > > > > the code looks like the arm code. Since the comment in the function
> > > > > indicates taht this is supposed to behave the same way as arm32 because
> > > >
> > > > Typo: s/taht/that/
> > > >
> > > > > it handles 32-bit tasks also.
> > > > >
> > > > > Cc: [email protected] # v3.16+
> > > > > Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
> > > > > Signed-off-by: Anders Roxell <[email protected]>
> > > >
> > > > The patch itself looks fine, but I don't think this needs a CC to
> > > > stable, nor does it require that fixes tag, as there's no functional
> > > > problem.
> > >
> > > Hmm... I now see I spoke too soon, and this is making the 1-byte
> > > breakpoint work at a 3-byte offset.
> >
> > I still don't think it's quite right though, since it forbids a 2-byte
> > watchpoint on a byte-aligned address.
>
> Plus, AFAICS, a 1-byte watchpoint on a 2-byte-aligned address.
>
> Not that I know anything about this code, but it does start to look like it
> might want rewriting without the offending switch statement anyway. At a
> glance, it looks like the intended semantic might boil down to:
>
> if (hw->ctrl.len > offset)
> return -EINVAL;
Given that it's compat code, I think it's worth staying as close to the
arch/arm/ implementation as we can. Also, beware that the
ARM_BREAKPOINT_LEN_* definitions are masks because of the BAS fields in
the debug architecture.
Will
On 26/07/2019 14:05, Will Deacon wrote:
> On Fri, Jul 26, 2019 at 01:38:24PM +0100, Robin Murphy wrote:
>> On 26/07/2019 13:27, Will Deacon wrote:
>>> On Fri, Jul 26, 2019 at 01:13:54PM +0100, Mark Rutland wrote:
>>>> On Fri, Jul 26, 2019 at 01:10:57PM +0100, Mark Rutland wrote:
>>>>> On Fri, Jul 26, 2019 at 01:27:16PM +0200, Anders Roxell wrote:
>>>>>> When fall-through warnings was enabled by default, commit d93512ef0f0e
>>>>>> ("Makefile: Globally enable fall-through warning"), the following
>>>>>> warnings was starting to show up:
>>>>>>
>>>>>> ../arch/arm64/kernel/hw_breakpoint.c: In function ‘hw_breakpoint_arch_parse’:
>>>>>> ../arch/arm64/kernel/hw_breakpoint.c:540:7: warning: this statement may fall
>>>>>> through [-Wimplicit-fallthrough=]
>>>>>> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
>>>>>> ^
>>>>>> ../arch/arm64/kernel/hw_breakpoint.c:542:3: note: here
>>>>>> case 2:
>>>>>> ^~~~
>>>>>> ../arch/arm64/kernel/hw_breakpoint.c:544:7: warning: this statement may fall
>>>>>> through [-Wimplicit-fallthrough=]
>>>>>> if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
>>>>>> ^
>>>>>> ../arch/arm64/kernel/hw_breakpoint.c:546:3: note: here
>>>>>> default:
>>>>>> ^~~~~~~
>>>>>>
>>>>>> Rework so that the compiler doesn't warn about fall-through. Rework so
>>>>>> the code looks like the arm code. Since the comment in the function
>>>>>> indicates taht this is supposed to behave the same way as arm32 because
>>>>>
>>>>> Typo: s/taht/that/
>>>>>
>>>>>> it handles 32-bit tasks also.
>>>>>>
>>>>>> Cc: [email protected] # v3.16+
>>>>>> Fixes: 6ee33c2712fc ("ARM: hw_breakpoint: correct and simplify alignment fixup code")
>>>>>> Signed-off-by: Anders Roxell <[email protected]>
>>>>>
>>>>> The patch itself looks fine, but I don't think this needs a CC to
>>>>> stable, nor does it require that fixes tag, as there's no functional
>>>>> problem.
>>>>
>>>> Hmm... I now see I spoke too soon, and this is making the 1-byte
>>>> breakpoint work at a 3-byte offset.
>>>
>>> I still don't think it's quite right though, since it forbids a 2-byte
>>> watchpoint on a byte-aligned address.
>>
>> Plus, AFAICS, a 1-byte watchpoint on a 2-byte-aligned address.
[and of course, what I missed was that that's the case the fallthrough
serves... yuck indeed]
>> Not that I know anything about this code, but it does start to look like it
>> might want rewriting without the offending switch statement anyway. At a
>> glance, it looks like the intended semantic might boil down to:
>>
>> if (hw->ctrl.len > offset)
>> return -EINVAL;
>
> Given that it's compat code, I think it's worth staying as close to the
> arch/arm/ implementation as we can.
Right, I also misread the accompanying arch/arm/ patch and got the
impression that 32-bit also had a problem such that any fix would happen
in parallel - on closer inspection the current arch/arm/ code does
actually seem to make sense, even if it is horribly subtle.
> Also, beware that the
> ARM_BREAKPOINT_LEN_* definitions are masks because of the BAS fields in
> the debug architecture.
Fun... Clearly it's a bit too Friday for me to be useful here, so
apologies for the confusion :)
Robin.