[Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya Srivastava]

Local symbols prefixed with '.L' do not emit symbol table entries, as
they have special meaning for the assembler.

'.L' prefixed symbols can be used within a code region, but should be
avoided for denoting a range of code via 'SYM_*_START/END' annotations.

Add a new check to emit warning on finding the usage of '.L' symbols
in '.S' files.

Suggested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7030c4d6d126..87d96a039e64 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3590,6 +3590,12 @@ sub process {
 			}
 		}
 
+# check for .L prefix local symbols in .S files
+		if ($realfile =~ /\.S$/ && $line =~ /\.L\S+/) {
+			WARN("AVOID_L_PREFIX",
+			     "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
+		}
+
 # check we are in a valid source file C or perl if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
 
-- 
2.17.1

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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Dwaipayan Ray]

On Sat, Jan 16, 2021 at 5:52 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
>
> Local symbols prefixed with '.L' do not emit symbol table entries, as
> they have special meaning for the assembler.
>
> '.L' prefixed symbols can be used within a code region, but should be
> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>
> Add a new check to emit warning on finding the usage of '.L' symbols
> in '.S' files.
>
> Suggested-by: Mark Brown <broonie@kernel.org>
> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
> ---
>  scripts/checkpatch.pl | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 7030c4d6d126..87d96a039e64 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -3590,6 +3590,12 @@ sub process {
>                         }
>                 }
>
> +# check for .L prefix local symbols in .S files
> +               if ($realfile =~ /\.S$/ && $line =~ /\.L\S+/) {
> +                       WARN("AVOID_L_PREFIX",
> +                            "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
> +               }
> +
>  # check we are in a valid source file C or perl if not then ignore this hunk
>                 next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
>
> --
> 2.17.1

From an earlier conversation:
>   So basically, you can use an .L symbol *inside* a function or a code
>   segment, you just can't use the .L symbol to contain the code using a
>   SYM_*_START/END annotation pair.

So this check warns on all uses of the .L prefix
I think that might be incorrect.

Thanks,
Dwaipayan.
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya]

On 16/1/21 6:13 pm, Dwaipayan Ray wrote:
> On Sat, Jan 16, 2021 at 5:52 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
>>
>> Local symbols prefixed with '.L' do not emit symbol table entries, as
>> they have special meaning for the assembler.
>>
>> '.L' prefixed symbols can be used within a code region, but should be
>> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>>
>> Add a new check to emit warning on finding the usage of '.L' symbols
>> in '.S' files.
>>
>> Suggested-by: Mark Brown <broonie@kernel.org>
>> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
>> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
>> ---
>>  scripts/checkpatch.pl | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>> index 7030c4d6d126..87d96a039e64 100755
>> --- a/scripts/checkpatch.pl
>> +++ b/scripts/checkpatch.pl
>> @@ -3590,6 +3590,12 @@ sub process {
>>                         }
>>                 }
>>
>> +# check for .L prefix local symbols in .S files
>> +               if ($realfile =~ /\.S$/ && $line =~ /\.L\S+/) {
>> +                       WARN("AVOID_L_PREFIX",
>> +                            "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
>> +               }
>> +
>>  # check we are in a valid source file C or perl if not then ignore this hunk
>>                 next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
>>
>> --
>> 2.17.1
> 
> From an earlier conversation:
>>   So basically, you can use an .L symbol *inside* a function or a code
>>   segment, you just can't use the .L symbol to contain the code using a
>>   SYM_*_START/END annotation pair.
> 
> So this check warns on all uses of the .L prefix
> I think that might be incorrect.
> 

Hey Dwaipayan,
I think you missed this:

> - If the line contains ".L" prefixed symbol, give user a
> warning/check, so that they can ensure that the line is not inside
> START/END block. (As we may not be able to make sure about the same,
> if the START/END line is not in the patch; otherwise we could run a
> while loop)

At best, I think, we could use $context_function, which should work
for patches, but again, this will not work for files.

Do you have any suggestions?

Thanks
Aditya
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Dwaipayan Ray]

On Sat, Jan 16, 2021 at 6:48 PM Aditya <yashsri421@gmail.com> wrote:
>
> On 16/1/21 6:13 pm, Dwaipayan Ray wrote:
> > On Sat, Jan 16, 2021 at 5:52 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
> >>
> >> Local symbols prefixed with '.L' do not emit symbol table entries, as
> >> they have special meaning for the assembler.
> >>
> >> '.L' prefixed symbols can be used within a code region, but should be
> >> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
> >>
> >> Add a new check to emit warning on finding the usage of '.L' symbols
> >> in '.S' files.
> >>
> >> Suggested-by: Mark Brown <broonie@kernel.org>
> >> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
> >> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
> >> ---
> >>  scripts/checkpatch.pl | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> >> index 7030c4d6d126..87d96a039e64 100755
> >> --- a/scripts/checkpatch.pl
> >> +++ b/scripts/checkpatch.pl
> >> @@ -3590,6 +3590,12 @@ sub process {
> >>                         }
> >>                 }
> >>
> >> +# check for .L prefix local symbols in .S files
> >> +               if ($realfile =~ /\.S$/ && $line =~ /\.L\S+/) {
> >> +                       WARN("AVOID_L_PREFIX",
> >> +                            "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
> >> +               }
> >> +
> >>  # check we are in a valid source file C or perl if not then ignore this hunk
> >>                 next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
> >>
> >> --
> >> 2.17.1
> >
> > From an earlier conversation:
> >>   So basically, you can use an .L symbol *inside* a function or a code
> >>   segment, you just can't use the .L symbol to contain the code using a
> >>   SYM_*_START/END annotation pair.
> >
> > So this check warns on all uses of the .L prefix
> > I think that might be incorrect.
> >
>
> Hey Dwaipayan,
> I think you missed this:
>
> > - If the line contains ".L" prefixed symbol, give user a
> > warning/check, so that they can ensure that the line is not inside
> > START/END block. (As we may not be able to make sure about the same,
> > if the START/END line is not in the patch; otherwise we could run a
> > while loop)
>

Then again what percentage of users actually intended to use
it in a local scope? That is actually a correct usage and checkpatch will
keep complaining - there will be no way to remove the warning.

> At best, I think, we could use $context_function, which should work
> for patches, but again, this will not work for files.
>
> Do you have any suggestions?
>

Does $context_function work for .S files? Am not sure.
But again that will not help much.

The main concern is not to allow .L prefix within a
SYM_*_START...SYM_*_END annotation pair.

That means something like this will be disallowed:

SYM_FUNC_START(memset)
    .L ... etc
SYM_FUNC_END(memset)

One possible way can be to extract the context after getting
a SYM_*_START. Following which the lines could be checked
for a .L preifx.

But complexity wise I dont know if it would be worth it.

Thanks & Regards,
Dwaipayan.
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya]

On 16/1/21 7:08 pm, Dwaipayan Ray wrote:
> On Sat, Jan 16, 2021 at 6:48 PM Aditya <yashsri421@gmail.com> wrote:
>>
>> On 16/1/21 6:13 pm, Dwaipayan Ray wrote:
>>> On Sat, Jan 16, 2021 at 5:52 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
>>>>
>>>> Local symbols prefixed with '.L' do not emit symbol table entries, as
>>>> they have special meaning for the assembler.
>>>>
>>>> '.L' prefixed symbols can be used within a code region, but should be
>>>> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>>>>
>>>> Add a new check to emit warning on finding the usage of '.L' symbols
>>>> in '.S' files.
>>>>
>>>> Suggested-by: Mark Brown <broonie@kernel.org>
>>>> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
>>>> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
>>>> ---
>>>>  scripts/checkpatch.pl | 6 ++++++
>>>>  1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>>>> index 7030c4d6d126..87d96a039e64 100755
>>>> --- a/scripts/checkpatch.pl
>>>> +++ b/scripts/checkpatch.pl
>>>> @@ -3590,6 +3590,12 @@ sub process {
>>>>                         }
>>>>                 }
>>>>
>>>> +# check for .L prefix local symbols in .S files
>>>> +               if ($realfile =~ /\.S$/ && $line =~ /\.L\S+/) {
>>>> +                       WARN("AVOID_L_PREFIX",
>>>> +                            "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
>>>> +               }
>>>> +
>>>>  # check we are in a valid source file C or perl if not then ignore this hunk
>>>>                 next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
>>>>
>>>> --
>>>> 2.17.1
>>>
>>> From an earlier conversation:
>>>>   So basically, you can use an .L symbol *inside* a function or a code
>>>>   segment, you just can't use the .L symbol to contain the code using a
>>>>   SYM_*_START/END annotation pair.
>>>
>>> So this check warns on all uses of the .L prefix
>>> I think that might be incorrect.
>>>
>>
>> Hey Dwaipayan,
>> I think you missed this:
>>
>>> - If the line contains ".L" prefixed symbol, give user a
>>> warning/check, so that they can ensure that the line is not inside
>>> START/END block. (As we may not be able to make sure about the same,
>>> if the START/END line is not in the patch; otherwise we could run a
>>> while loop)
>>
> 
> Then again what percentage of users actually intended to use
> it in a local scope? That is actually a correct usage and checkpatch will
> keep complaining - there will be no way to remove the warning.
> 
>> At best, I think, we could use $context_function, which should work
>> for patches, but again, this will not work for files.
>>
>> Do you have any suggestions?
>>
> 
> Does $context_function work for .S files? Am not sure.> But again that will not help much.
> 
> The main concern is not to allow .L prefix within a
> SYM_*_START...SYM_*_END annotation pair.
> 
> That means something like this will be disallowed:
> 
> SYM_FUNC_START(memset)
>     .L ... etc
> SYM_FUNC_END(memset)
> 

Yes, $context_function works inside .S files.
So, I think if it is inside one of the SYM_*_START contexts, it should
work for us.

> One possible way can be to extract the context after getting
> a SYM_*_START. Following which the lines could be checked
> for a .L preifx.
> > But complexity wise I dont know if it would be worth it.
> 

I think, we could do this for files.

But I am not sure about the complexity part.
Lukas, what do you think?

Thanks
Aditya
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Lukas Bulwahn]

On Sat, Jan 16, 2021 at 3:57 PM Aditya <yashsri421@gmail.com> wrote:
>
> On 16/1/21 7:08 pm, Dwaipayan Ray wrote:
> > On Sat, Jan 16, 2021 at 6:48 PM Aditya <yashsri421@gmail.com> wrote:
> >>
> >> On 16/1/21 6:13 pm, Dwaipayan Ray wrote:
> >>> On Sat, Jan 16, 2021 at 5:52 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
> >>>>
> >>>> Local symbols prefixed with '.L' do not emit symbol table entries, as
> >>>> they have special meaning for the assembler.
> >>>>
> >>>> '.L' prefixed symbols can be used within a code region, but should be
> >>>> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
> >>>>
> >>>> Add a new check to emit warning on finding the usage of '.L' symbols
> >>>> in '.S' files.
> >>>>
> >>>> Suggested-by: Mark Brown <broonie@kernel.org>
> >>>> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
> >>>> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
> >>>> ---
> >>>>  scripts/checkpatch.pl | 6 ++++++
> >>>>  1 file changed, 6 insertions(+)
> >>>>
> >>>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> >>>> index 7030c4d6d126..87d96a039e64 100755
> >>>> --- a/scripts/checkpatch.pl
> >>>> +++ b/scripts/checkpatch.pl
> >>>> @@ -3590,6 +3590,12 @@ sub process {
> >>>>                         }
> >>>>                 }
> >>>>
> >>>> +# check for .L prefix local symbols in .S files
> >>>> +               if ($realfile =~ /\.S$/ && $line =~ /\.L\S+/) {
> >>>> +                       WARN("AVOID_L_PREFIX",
> >>>> +                            "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
> >>>> +               }
> >>>> +
> >>>>  # check we are in a valid source file C or perl if not then ignore this hunk
> >>>>                 next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
> >>>>
> >>>> --
> >>>> 2.17.1
> >>>
> >>> From an earlier conversation:
> >>>>   So basically, you can use an .L symbol *inside* a function or a code
> >>>>   segment, you just can't use the .L symbol to contain the code using a
> >>>>   SYM_*_START/END annotation pair.
> >>>
> >>> So this check warns on all uses of the .L prefix
> >>> I think that might be incorrect.
> >>>
> >>
> >> Hey Dwaipayan,
> >> I think you missed this:
> >>
> >>> - If the line contains ".L" prefixed symbol, give user a
> >>> warning/check, so that they can ensure that the line is not inside
> >>> START/END block. (As we may not be able to make sure about the same,
> >>> if the START/END line is not in the patch; otherwise we could run a
> >>> while loop)
> >>
> >
> > Then again what percentage of users actually intended to use
> > it in a local scope? That is actually a correct usage and checkpatch will
> > keep complaining - there will be no way to remove the warning.
> >
> >> At best, I think, we could use $context_function, which should work
> >> for patches, but again, this will not work for files.
> >>
> >> Do you have any suggestions?
> >>
> >
> > Does $context_function work for .S files? Am not sure.> But again that will not help much.
> >
> > The main concern is not to allow .L prefix within a
> > SYM_*_START...SYM_*_END annotation pair.
> >
> > That means something like this will be disallowed:
> >
> > SYM_FUNC_START(memset)
> >     .L ... etc
> > SYM_FUNC_END(memset)
> >
>
> Yes, $context_function works inside .S files.
> So, I think if it is inside one of the SYM_*_START contexts, it should
> work for us.
>
> > One possible way can be to extract the context after getting
> > a SYM_*_START. Following which the lines could be checked
> > for a .L preifx.
> > > But complexity wise I dont know if it would be worth it.
> >
>
> I think, we could do this for files.
>

Just run it on the current kernel source and find out how many cases
would generally match.

If it is just a few hundred occurrences, use a simple rule, not a
complex one that hardly works on patches.

Lukas
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[Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya Srivastava]

Local symbols prefixed with '.L' do not emit symbol table entries, as
they have special meaning for the assembler.

'.L' prefixed symbols can be used within a code region, but should be
avoided for denoting a range of code via 'SYM_*_START/END' annotations.

Add a new check to emit warning on finding the usage of '.L' symbols
in '.S' files, if it lies within SYM_*_START/END annotation pair.

Suggested-by: Mark Brown <bro...@kernel.org>
Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
---
 scripts/checkpatch.pl | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7030c4d6d126..858b5def61e9 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2501,6 +2501,9 @@ sub process {
 
 	my $checklicenseline = 1;
 
+	# record SYM_*_START/END annotation pair count, for AVOID_L_PREFIX
+	my $sym_start_block = 0;
+
 	sanitise_line_reset();
 	my $line;
 	foreach my $rawline (@rawlines) {
@@ -3590,6 +3593,25 @@ sub process {
 			}
 		}
 
+# check for .L prefix local symbols in .S files
+		if ($realfile =~ /\.S$/) {
+			if ($line =~ /SYM_.*_START/ ||
+			    (defined $context_function && $context_function =~ /SYM_.*_START/)) {
+				$sym_start_block++;
+			}
+
+			if ($line=~ /\.L\S+/ &&		# line contains .L prefixed local symbol
+			    $sym_start_block > 0) {	# lies between SYM_*_START and SYM_*_END pair
+				WARN("AVOID_L_PREFIX",
+					"Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
+			}
+
+			if ($line =~ /SYM_.*_END/ ||
+			    (defined $context_function && $context_function =~ /SYM_.*_END/)) {
+				$sym_start_block--;
+			}
+		}
+
 # check we are in a valid source file C or perl if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
 
-- 
2.17.1

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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Lukas Bulwahn]

On Mon, Jan 18, 2021 at 3:44 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
>
> Local symbols prefixed with '.L' do not emit symbol table entries, as
> they have special meaning for the assembler.
>
> '.L' prefixed symbols can be used within a code region, but should be
> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>
> Add a new check to emit warning on finding the usage of '.L' symbols

to emit a warning

> in '.S' files, if it lies within SYM_*_START/END annotation pair.
>
> Suggested-by: Mark Brown <bro...@kernel.org>

Hmm, that is not an email?

Did you test running it on the patch that introduced the bug initially
which then led to the overall discussion I pointed out to you?

Lukas

> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
> ---
>  scripts/checkpatch.pl | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 7030c4d6d126..858b5def61e9 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -2501,6 +2501,9 @@ sub process {
>
>         my $checklicenseline = 1;
>
> +       # record SYM_*_START/END annotation pair count, for AVOID_L_PREFIX
> +       my $sym_start_block = 0;
> +
>         sanitise_line_reset();
>         my $line;
>         foreach my $rawline (@rawlines) {
> @@ -3590,6 +3593,25 @@ sub process {
>                         }
>                 }
>
> +# check for .L prefix local symbols in .S files
> +               if ($realfile =~ /\.S$/) {
> +                       if ($line =~ /SYM_.*_START/ ||
> +                           (defined $context_function && $context_function =~ /SYM_.*_START/)) {
> +                               $sym_start_block++;
> +                       }
> +
> +                       if ($line=~ /\.L\S+/ &&         # line contains .L prefixed local symbol
> +                           $sym_start_block > 0) {     # lies between SYM_*_START and SYM_*_END pair
> +                               WARN("AVOID_L_PREFIX",
> +                                       "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
> +                       }
> +
> +                       if ($line =~ /SYM_.*_END/ ||
> +                           (defined $context_function && $context_function =~ /SYM_.*_END/)) {
> +                               $sym_start_block--;
> +                       }
> +               }
> +
>  # check we are in a valid source file C or perl if not then ignore this hunk
>                 next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
>
> --
> 2.17.1
>
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya]

On 18/1/21 10:54 pm, Lukas Bulwahn wrote:
> On Mon, Jan 18, 2021 at 3:44 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
>>
>> Local symbols prefixed with '.L' do not emit symbol table entries, as
>> they have special meaning for the assembler.
>>
>> '.L' prefixed symbols can be used within a code region, but should be
>> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>>
>> Add a new check to emit warning on finding the usage of '.L' symbols
> 
> to emit a warning
> 

Okay

>> in '.S' files, if it lies within SYM_*_START/END annotation pair.
>>
>> Suggested-by: Mark Brown <bro...@kernel.org>
> 
> Hmm, that is not an email?
> 

Oops, I'll fix it.

> Did you test running it on the patch that introduced the bug initially
> which then led to the overall discussion I pointed out to you?
> 

Hi Lukas
So, the patch led to the initial discussion was probably this:
https://groups.google.com/g/clang-built-linux/c/1C6YoJKBsQQ/m/a8IS1NjGAgAJ

This patch is related to changes made in tools/objtool. So, we
probably cannot test this patch for AVOID_L_PREFIX warning.

I'll walk you through the discussion:

Because of the above changes in objtool, [PATCH] x86/entry: use
STB_GLOBAL for register restoring thunk was proposed
(https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/qWnKkZWFBgAJ)

It was later decided that the changes can be instead made to .L prefix
local symbols here for avoiding the objtool warning:
https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/MtjkJK6LCgAJ

And for standardizing this practice, the suggestion for checkpatch
rule was made here:
https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/4staOlf-CgAJ

However, I have tested the patch on arch/x86/ files and also the patch
proposed here fixing for one of those files.

As expected, I got no warnings for the patch fixing the warnings for
thunk_64.S file, and some warnings for files where the prefix was used.

Thanks
Aditya
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[Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya Srivastava]

Local symbols prefixed with '.L' do not emit symbol table entries, as
they have special meaning for the assembler.

'.L' prefixed symbols can be used within a code region, but should be
avoided for denoting a range of code via 'SYM_*_START/END' annotations.

Add a new check to emit a warning on finding the usage of '.L' symbols
in '.S' files, if it lies within SYM_*_START/END annotation pair.

Suggested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
---
 scripts/checkpatch.pl | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7030c4d6d126..858b5def61e9 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2501,6 +2501,9 @@ sub process {
 
 	my $checklicenseline = 1;
 
+	# record SYM_*_START/END annotation pair count, for AVOID_L_PREFIX
+	my $sym_start_block = 0;
+
 	sanitise_line_reset();
 	my $line;
 	foreach my $rawline (@rawlines) {
@@ -3590,6 +3593,25 @@ sub process {
 			}
 		}
 
+# check for .L prefix local symbols in .S files
+		if ($realfile =~ /\.S$/) {
+			if ($line =~ /SYM_.*_START/ ||
+			    (defined $context_function && $context_function =~ /SYM_.*_START/)) {
+				$sym_start_block++;
+			}
+
+			if ($line=~ /\.L\S+/ &&		# line contains .L prefixed local symbol
+			    $sym_start_block > 0) {	# lies between SYM_*_START and SYM_*_END pair
+				WARN("AVOID_L_PREFIX",
+					"Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
+			}
+
+			if ($line =~ /SYM_.*_END/ ||
+			    (defined $context_function && $context_function =~ /SYM_.*_END/)) {
+				$sym_start_block--;
+			}
+		}
+
 # check we are in a valid source file C or perl if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
 
-- 
2.17.1

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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Lukas Bulwahn]

On Mon, Jan 18, 2021 at 8:14 PM Aditya Srivastava <yashsri421@gmail.com> wrote:
>
> Local symbols prefixed with '.L' do not emit symbol table entries, as
> they have special meaning for the assembler.
>
> '.L' prefixed symbols can be used within a code region, but should be
> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>
> Add a new check to emit a warning on finding the usage of '.L' symbols
> in '.S' files, if it lies within SYM_*_START/END annotation pair.
>
> Suggested-by: Mark Brown <broonie@kernel.org>
> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
> Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
> ---

Okay, send it out to the initial discussion group (with the standard
CCs for mentees and checkpatch) and lkml. Then we see.

Lukas
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Fāng-ruì Sòng via Linux-kernel-mentees]

On Fri, Jan 22, 2021 at 12:13 PM Aditya <yashsri421@gmail.com> wrote:
>
> On 23/1/21 12:40 am, Joe Perches wrote:
> > On Fri, 2021-01-22 at 18:48 +0530, Aditya wrote:
> >> On 21/1/21 12:13 am, Joe Perches wrote:
> >>> I believe the test should be:
> >>>
> >>>     if ($realfile =~ /\.S$/ &&
> >>>         $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
> >>
> >> Joe, with this regex, we won't be able to match
> >> "jmp  .L_restore
> >> SYM_FUNC_END(\name)"
> >
> > I think that's not an issue.
> >
> >> which was replaced in this patch in the discussion:
> >> https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/phKe-Tb6CgAJ
> >>
> >> Here, "jmp  .L_restore" was also replaced to fix the error.
> >
> > Notice that this line was also replaced in the same patch:
> >
> >  #ifdef CONFIG_PREEMPTION
> > -SYM_CODE_START_LOCAL_NOALIGN(.L_restore)
> > +SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore)
> >
> >
> >> However, if this
> >> regex(/^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) is
> >> correct, maybe we don't need to check for $file as we are now checking
> >> for just one line.
> >>
> >> What do you think?
> >
> > The test I wrote was complete, did not use $file and emits a
> > warning on the use of CODE_SYM_START_LOCAL_NOALIGN(.L_restore)
> >
> > I think it's sufficient.
> >
>
> Okay, Thanks.. I will send the modified patch :)
>
> Thanks
> Aditya

I am slightly concerned with the direction here.   jmp .Lsym is fine
and is probably preferable in cases where you absolutely want to emit
a local symbol.
(there is a related -z unique-symbol GNU ld+FGKASLR thing I shall
analyze in my spare time)

If the problem is just that STT_SECTION symbols are missing, can
objtool do something to conceptually synthesize them?
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya]

On 23/1/21 12:40 am, Joe Perches wrote:
> On Fri, 2021-01-22 at 18:48 +0530, Aditya wrote:
>> On 21/1/21 12:13 am, Joe Perches wrote:
>>> I believe the test should be:
>>>
>>> 	if ($realfile =~ /\.S$/ &&
>>> 	    $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
>>
>> Joe, with this regex, we won't be able to match
>> "jmp  .L_restore
>> SYM_FUNC_END(\name)"
> 
> I think that's not an issue.
> 
>> which was replaced in this patch in the discussion:
>> https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/phKe-Tb6CgAJ
>>
>> Here, "jmp  .L_restore" was also replaced to fix the error.
> 
> Notice that this line was also replaced in the same patch:
> 
>  #ifdef CONFIG_PREEMPTION
> -SYM_CODE_START_LOCAL_NOALIGN(.L_restore)
> +SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore)
> 
> 
>> However, if this
>> regex(/^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) is
>> correct, maybe we don't need to check for $file as we are now checking
>> for just one line.
>>
>> What do you think?
> 
> The test I wrote was complete, did not use $file and emits a
> warning on the use of CODE_SYM_START_LOCAL_NOALIGN(.L_restore)
> 
> I think it's sufficient.
> 

Okay, Thanks.. I will send the modified patch :)

Thanks
Aditya
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Joe Perches]

On Fri, 2021-01-22 at 18:48 +0530, Aditya wrote:
> On 21/1/21 12:13 am, Joe Perches wrote:
> > I believe the test should be:
> > 
> > 	if ($realfile =~ /\.S$/ &&
> > 	    $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
> 
> Joe, with this regex, we won't be able to match
> "jmp  .L_restore
> SYM_FUNC_END(\name)"

I think that's not an issue.

> which was replaced in this patch in the discussion:
> https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/phKe-Tb6CgAJ
> 
> Here, "jmp  .L_restore" was also replaced to fix the error.

Notice that this line was also replaced in the same patch:

 #ifdef CONFIG_PREEMPTION
-SYM_CODE_START_LOCAL_NOALIGN(.L_restore)
+SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore)


> However, if this
> regex(/^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) is
> correct, maybe we don't need to check for $file as we are now checking
> for just one line.
> 
> What do you think?

The test I wrote was complete, did not use $file and emits a
warning on the use of CODE_SYM_START_LOCAL_NOALIGN(.L_restore)

I think it's sufficient.

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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya]

On 21/1/21 12:13 am, Joe Perches wrote:
> On Wed, 2021-01-20 at 18:23 +0530, Aditya wrote:
>> On 20/1/21 2:51 pm, Joe Perches wrote:
>>> On Wed, 2021-01-20 at 12:55 +0530, Aditya Srivastava wrote:
>>>> Local symbols prefixed with '.L' do not emit symbol table entries, as
>>>> they have special meaning for the assembler.
>>>>
>>>> '.L' prefixed symbols can be used within a code region, but should be
>>>> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>>>>
>>>> Add a new check to emit a warning on finding the usage of '.L' symbols
>>>> in '.S' files, if it lies within SYM_*_START/END annotation pair.
>>>
>>> I believe this needs a test for $file as it won't work well on
>>> patches as the SYM_*_START/END may not be in the patch context.
>>>
>> Okay.
>>
>>> Also, is this supposed to work for local labels like '.L<foo>:'?
>>> I don't think a warning should be generated for those.
>>>
>> Yes, currently it will generate warning for all symbols which start
>> with .L and have non- white character symbol following it, if it is
>> lying within SYM_*_START/END annotation pair.
>>
>> Should I reduce the check to \.L_\S+ instead? (please note "_"
>> following ".L")
> 
> Use grep first.  That would still match several existing labels.
> 
>> Pardon me, I'm not good with assembly :/
> 
> Spending time reading docs can help with that.
> 
> Mark?  Can you please comment about the below?
> 
> I believe the test should be:
> 
> 	if ($realfile =~ /\.S$/ &&
> 	    $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {

Joe, with this regex, we won't be able to match
"jmp  .L_restore
SYM_FUNC_END(\name)"

which was replaced in this patch in the discussion:
https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/phKe-Tb6CgAJ

Here, "jmp  .L_restore" was also replaced to fix the error.

However, if this
regex(/^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) is
correct, maybe we don't need to check for $file as we are now checking
for just one line.

What do you think?

Thanks
Aditya

> 		WARN(...);
> 	}
> 
> so that only this code currently matches:
> 
> $ git grep -P '^\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L' -- '*.S'
> arch/x86/boot/compressed/head_32.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> arch/x86/boot/compressed/head_32.S:SYM_FUNC_END(.Lrelocated)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lrelocated)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lpaging_enabled)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lno_longmode)
> arch/x86/boot/pmjump.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
> arch/x86/boot/pmjump.S:SYM_FUNC_END(.Lin_pm32)
> arch/x86/entry/entry_64.S:SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
> arch/x86/entry/entry_64.S:SYM_CODE_END(.Lbad_gs)
> arch/x86/lib/copy_user_64.S:SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
> arch/x86/lib/copy_user_64.S:SYM_CODE_END(.Lcopy_user_handle_tail)
> arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_clac)
> arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_clac)
> arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_8_clac)
> arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_8_clac)
> arch/x86/lib/putuser.S:SYM_CODE_START_LOCAL(.Lbad_put_user_clac)
> arch/x86/lib/putuser.S:SYM_CODE_END(.Lbad_put_user_clac)
> arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_START_LOCAL(.Lwakeup_idt)
> arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_END(.Lwakeup_idt)
> 
> 

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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Josh Poimboeuf]

On Wed, Jan 20, 2021 at 10:57:03AM -0800, Nick Desaulniers wrote:
> > $ git grep -P '^\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L' -- '*.S'
> > arch/x86/boot/compressed/head_32.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> > arch/x86/boot/compressed/head_32.S:SYM_FUNC_END(.Lrelocated)
> > arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> > arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lrelocated)
> > arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
> > arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lpaging_enabled)
> > arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode)
> > arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lno_longmode)
> > arch/x86/boot/pmjump.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
> > arch/x86/boot/pmjump.S:SYM_FUNC_END(.Lin_pm32)
> > arch/x86/entry/entry_64.S:SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
> > arch/x86/entry/entry_64.S:SYM_CODE_END(.Lbad_gs)
> > arch/x86/lib/copy_user_64.S:SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
> > arch/x86/lib/copy_user_64.S:SYM_CODE_END(.Lcopy_user_handle_tail)
> > arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_clac)
> > arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_clac)
> > arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_8_clac)
> > arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_8_clac)
> > arch/x86/lib/putuser.S:SYM_CODE_START_LOCAL(.Lbad_put_user_clac)
> > arch/x86/lib/putuser.S:SYM_CODE_END(.Lbad_put_user_clac)
> > arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_START_LOCAL(.Lwakeup_idt)
> > arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_END(.Lwakeup_idt)
> 
> Josh, I assume objtool does not annotate code under:
> arch/x86/boot/
> arch/x86/entry/
> arch/x86/realmode/
> ?
> 
> The rest, ie
> arch/x86/lib/
> seem potentially relevant?

Both arch/x86/entry/* and arch/x86/lib/* are read by objtool and should
probably be fixed up.

-- 
Josh

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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Nick Desaulniers via Linux-kernel-mentees]

On Wed, Jan 20, 2021 at 10:43 AM Joe Perches <joe@perches.com> wrote:
>
> On Wed, 2021-01-20 at 18:23 +0530, Aditya wrote:
> > On 20/1/21 2:51 pm, Joe Perches wrote:
> > > On Wed, 2021-01-20 at 12:55 +0530, Aditya Srivastava wrote:
> > > > Local symbols prefixed with '.L' do not emit symbol table entries, as
> > > > they have special meaning for the assembler.
> > > >
> > > > '.L' prefixed symbols can be used within a code region, but should be
> > > > avoided for denoting a range of code via 'SYM_*_START/END' annotations.
> > > >
> > > > Add a new check to emit a warning on finding the usage of '.L' symbols
> > > > in '.S' files, if it lies within SYM_*_START/END annotation pair.
> > >
> > > I believe this needs a test for $file as it won't work well on
> > > patches as the SYM_*_START/END may not be in the patch context.
> > >
> > Okay.
> >
> > > Also, is this supposed to work for local labels like '.L<foo>:'?
> > > I don't think a warning should be generated for those.
> > >
> > Yes, currently it will generate warning for all symbols which start
> > with .L and have non- white character symbol following it, if it is
> > lying within SYM_*_START/END annotation pair.
> >
> > Should I reduce the check to \.L_\S+ instead? (please note "_"
> > following ".L")
>
> Use grep first.  That would still match several existing labels.
>
> > Pardon me, I'm not good with assembly :/
>
> Spending time reading docs can help with that.
>
> Mark?  Can you please comment about the below?
>
> I believe the test should be:
>
>         if ($realfile =~ /\.S$/ &&
>             $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
>                 WARN(...);
>         }
>
> so that only this code currently matches:
>
> $ git grep -P '^\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L' -- '*.S'
> arch/x86/boot/compressed/head_32.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> arch/x86/boot/compressed/head_32.S:SYM_FUNC_END(.Lrelocated)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lrelocated)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lpaging_enabled)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode)
> arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lno_longmode)
> arch/x86/boot/pmjump.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
> arch/x86/boot/pmjump.S:SYM_FUNC_END(.Lin_pm32)
> arch/x86/entry/entry_64.S:SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
> arch/x86/entry/entry_64.S:SYM_CODE_END(.Lbad_gs)
> arch/x86/lib/copy_user_64.S:SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
> arch/x86/lib/copy_user_64.S:SYM_CODE_END(.Lcopy_user_handle_tail)
> arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_clac)
> arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_clac)
> arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_8_clac)
> arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_8_clac)
> arch/x86/lib/putuser.S:SYM_CODE_START_LOCAL(.Lbad_put_user_clac)
> arch/x86/lib/putuser.S:SYM_CODE_END(.Lbad_put_user_clac)
> arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_START_LOCAL(.Lwakeup_idt)
> arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_END(.Lwakeup_idt)

Josh, I assume objtool does not annotate code under:
arch/x86/boot/
arch/x86/entry/
arch/x86/realmode/
?

The rest, ie
arch/x86/lib/
seem potentially relevant?
-- 
Thanks,
~Nick Desaulniers
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Joe Perches]

On Wed, 2021-01-20 at 18:23 +0530, Aditya wrote:
> On 20/1/21 2:51 pm, Joe Perches wrote:
> > On Wed, 2021-01-20 at 12:55 +0530, Aditya Srivastava wrote:
> > > Local symbols prefixed with '.L' do not emit symbol table entries, as
> > > they have special meaning for the assembler.
> > > 
> > > '.L' prefixed symbols can be used within a code region, but should be
> > > avoided for denoting a range of code via 'SYM_*_START/END' annotations.
> > > 
> > > Add a new check to emit a warning on finding the usage of '.L' symbols
> > > in '.S' files, if it lies within SYM_*_START/END annotation pair.
> > 
> > I believe this needs a test for $file as it won't work well on
> > patches as the SYM_*_START/END may not be in the patch context.
> > 
> Okay.
> 
> > Also, is this supposed to work for local labels like '.L<foo>:'?
> > I don't think a warning should be generated for those.
> > 
> Yes, currently it will generate warning for all symbols which start
> with .L and have non- white character symbol following it, if it is
> lying within SYM_*_START/END annotation pair.
> 
> Should I reduce the check to \.L_\S+ instead? (please note "_"
> following ".L")

Use grep first.  That would still match several existing labels.

> Pardon me, I'm not good with assembly :/

Spending time reading docs can help with that.

Mark?  Can you please comment about the below?

I believe the test should be:

	if ($realfile =~ /\.S$/ &&
	    $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
		WARN(...);
	}

so that only this code currently matches:

$ git grep -P '^\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L' -- '*.S'
arch/x86/boot/compressed/head_32.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
arch/x86/boot/compressed/head_32.S:SYM_FUNC_END(.Lrelocated)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lrelocated)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lpaging_enabled)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lno_longmode)
arch/x86/boot/pmjump.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
arch/x86/boot/pmjump.S:SYM_FUNC_END(.Lin_pm32)
arch/x86/entry/entry_64.S:SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
arch/x86/entry/entry_64.S:SYM_CODE_END(.Lbad_gs)
arch/x86/lib/copy_user_64.S:SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
arch/x86/lib/copy_user_64.S:SYM_CODE_END(.Lcopy_user_handle_tail)
arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_clac)
arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_clac)
arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_8_clac)
arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_8_clac)
arch/x86/lib/putuser.S:SYM_CODE_START_LOCAL(.Lbad_put_user_clac)
arch/x86/lib/putuser.S:SYM_CODE_END(.Lbad_put_user_clac)
arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_START_LOCAL(.Lwakeup_idt)
arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_END(.Lwakeup_idt)


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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya]

On 20/1/21 2:51 pm, Joe Perches wrote:
> On Wed, 2021-01-20 at 12:55 +0530, Aditya Srivastava wrote:
>> Local symbols prefixed with '.L' do not emit symbol table entries, as
>> they have special meaning for the assembler.
>>
>> '.L' prefixed symbols can be used within a code region, but should be
>> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
>>
>> Add a new check to emit a warning on finding the usage of '.L' symbols
>> in '.S' files, if it lies within SYM_*_START/END annotation pair.
> 
> I believe this needs a test for $file as it won't work well on
> patches as the SYM_*_START/END may not be in the patch context.
> 
Okay.

> Also, is this supposed to work for local labels like '.L<foo>:'?
> I don't think a warning should be generated for those.
> 
Yes, currently it will generate warning for all symbols which start
with .L and have non- white character symbol following it, if it is
lying within SYM_*_START/END annotation pair.

Should I reduce the check to \.L_\S+ instead? (please note "_"
following ".L")
Pardon me, I'm not good with assembly :/

Thanks
Aditya
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Re: [Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Joe Perches]

On Wed, 2021-01-20 at 12:55 +0530, Aditya Srivastava wrote:
> Local symbols prefixed with '.L' do not emit symbol table entries, as
> they have special meaning for the assembler.
> 
> '.L' prefixed symbols can be used within a code region, but should be
> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
> 
> Add a new check to emit a warning on finding the usage of '.L' symbols
> in '.S' files, if it lies within SYM_*_START/END annotation pair.

I believe this needs a test for $file as it won't work well on
patches as the SYM_*_START/END may not be in the patch context.

Also, is this supposed to work for local labels like '.L<foo>:'?
I don't think a warning should be generated for those.


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[Linux-kernel-mentees] [PATCH] checkpatch: add warning for avoiding .L prefix symbols in assembly files

[Aditya Srivastava]

Local symbols prefixed with '.L' do not emit symbol table entries, as
they have special meaning for the assembler.

'.L' prefixed symbols can be used within a code region, but should be
avoided for denoting a range of code via 'SYM_*_START/END' annotations.

Add a new check to emit a warning on finding the usage of '.L' symbols
in '.S' files, if it lies within SYM_*_START/END annotation pair.

Suggested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk/
Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
---
 scripts/checkpatch.pl | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7030c4d6d126..858b5def61e9 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2501,6 +2501,9 @@ sub process {
 
 	my $checklicenseline = 1;
 
+	# record SYM_*_START/END annotation pair count, for AVOID_L_PREFIX
+	my $sym_start_block = 0;
+
 	sanitise_line_reset();
 	my $line;
 	foreach my $rawline (@rawlines) {
@@ -3590,6 +3593,25 @@ sub process {
 			}
 		}
 
+# check for .L prefix local symbols in .S files
+		if ($realfile =~ /\.S$/) {
+			if ($line =~ /SYM_.*_START/ ||
+			    (defined $context_function && $context_function =~ /SYM_.*_START/)) {
+				$sym_start_block++;
+			}
+
+			if ($line=~ /\.L\S+/ &&		# line contains .L prefixed local symbol
+			    $sym_start_block > 0) {	# lies between SYM_*_START and SYM_*_END pair
+				WARN("AVOID_L_PREFIX",
+					"Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
+			}
+
+			if ($line =~ /SYM_.*_END/ ||
+			    (defined $context_function && $context_function =~ /SYM_.*_END/)) {
+				$sym_start_block--;
+			}
+		}
+
 # check we are in a valid source file C or perl if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
 
-- 
2.17.1

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