[PATCH for-4.7] xen/build: Fix build with Clang

[PATCH for-4.7] xen/build: Fix build with Clang

[Andrew Cooper]

c/s 607044bf9 "build: avoid putting local absolute symbols in symbol tables"
breaks the build with Clang, as the command line argument isn't understood.

Clang does not appear to have any equivielent option, and already has
outstanding issues with duplicate symbols.  Excluding this option makes the
problem no worse.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>

The clang build already has many duplicate symbols for some reason I have yet
to identify, e.g.

  Duplicate symbol 'asid.c#get_cpu_info' (ffff82d0801e6840 != ffff82d0801c8190)
  Duplicate symbol 'ats.c#__list_add' (ffff82d08015b900 != ffff82d0801546a0)
  Duplicate symbol 'common.c#clear_bit' (ffff82d080213560 != ffff82d0801baf10)
  Duplicate symbol 'common.c#constant_test_bit' (ffff82d080213550 != ffff82d0801ba750)
  Duplicate symbol 'common.c#cpumask_check' (ffff82d080218c50 != ffff82d0801baf20)
  Duplicate symbol 'common.c#cpumask_clear_cpu' (ffff82d080214990 != ffff82d0801bae40)
  Duplicate symbol 'common.c#get_cpu_info' (ffff82d080212210 != ffff82d0801bad20)

The resulting binary does function.  Someone with more time can investigate
making symbol handling work better with Clang
---
 xen/Rules.mk | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index d4dffde..7183d69 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
 CFLAGS += -nostdinc -fno-builtin -fno-common
 CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
-CFLAGS += -Wa,--strip-local-absolute
 CFLAGS += '-D__OBJECT_FILE__="$@"'
 
+ifneq ($(clang),y)
+# Clang doesn't understand this command line argument, and doesn't appear to
+# have an suitable alternative.  The resulting compiled binary does function,
+# but has an excessively large symbol table.
+CFLAGS += -Wa,--strip-local-absolute
+endif
+
 CFLAGS-$(verbose)       += -DVERBOSE
 CFLAGS-$(crash_debug)   += -DCRASH_DEBUG
 CFLAGS-$(perfc)         += -DPERF_COUNTERS
-- 
2.1.4


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Re: [PATCH for-4.7] xen/build: Fix build with Clang

[Jan Beulich]

>>> On 07.04.16 at 20:46, <andrew.cooper3@citrix.com> wrote:
> The clang build already has many duplicate symbols for some reason I have yet
> to identify, e.g.
> 
>   Duplicate symbol 'asid.c#get_cpu_info' (ffff82d0801e6840 != ffff82d0801c8190)
>   Duplicate symbol 'ats.c#__list_add' (ffff82d08015b900 != ffff82d0801546a0)
>   Duplicate symbol 'common.c#clear_bit' (ffff82d080213560 != ffff82d0801baf10)
>   Duplicate symbol 'common.c#constant_test_bit' (ffff82d080213550 != ffff82d0801ba750)
>   Duplicate symbol 'common.c#cpumask_check' (ffff82d080218c50 != ffff82d0801baf20)
>   Duplicate symbol 'common.c#cpumask_clear_cpu' (ffff82d080214990 != ffff82d0801bae40)
>   Duplicate symbol 'common.c#get_cpu_info' (ffff82d080212210 != ffff82d0801bad20)
> 
> The resulting binary does function.  Someone with more time can investigate
> making symbol handling work better with Clang

I'd guess that's because they don't inline functions as aggressively
as gcc does.

> --- a/xen/Rules.mk
> +++ b/xen/Rules.mk
> @@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
>  CFLAGS += -nostdinc -fno-builtin -fno-common
>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
> -CFLAGS += -Wa,--strip-local-absolute
>  CFLAGS += '-D__OBJECT_FILE__="$@"'
>  
> +ifneq ($(clang),y)
> +# Clang doesn't understand this command line argument, and doesn't appear to
> +# have an suitable alternative.  The resulting compiled binary does function,
> +# but has an excessively large symbol table.
> +CFLAGS += -Wa,--strip-local-absolute
> +endif

Well, that's the brute force undo-it-altogether-for-clang approach
that I think Doug had also considered. You may have seen the
discussion (on irc iirc) - I'd really like to see the option still getting
passed to gas (for all the .S files) even when using clang. Would
that really be hard to arrange for?

Jan


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Re: [PATCH for-4.7] xen/build: Fix build with Clang

[Andrew Cooper]

On 07/04/16 20:12, Jan Beulich wrote:
>>>> On 07.04.16 at 20:46, <andrew.cooper3@citrix.com> wrote:
>> The clang build already has many duplicate symbols for some reason I have yet
>> to identify, e.g.
>>
>>   Duplicate symbol 'asid.c#get_cpu_info' (ffff82d0801e6840 != ffff82d0801c8190)
>>   Duplicate symbol 'ats.c#__list_add' (ffff82d08015b900 != ffff82d0801546a0)
>>   Duplicate symbol 'common.c#clear_bit' (ffff82d080213560 != ffff82d0801baf10)
>>   Duplicate symbol 'common.c#constant_test_bit' (ffff82d080213550 != ffff82d0801ba750)
>>   Duplicate symbol 'common.c#cpumask_check' (ffff82d080218c50 != ffff82d0801baf20)
>>   Duplicate symbol 'common.c#cpumask_clear_cpu' (ffff82d080214990 != ffff82d0801bae40)
>>   Duplicate symbol 'common.c#get_cpu_info' (ffff82d080212210 != ffff82d0801bad20)
>>
>> The resulting binary does function.  Someone with more time can investigate
>> making symbol handling work better with Clang
> I'd guess that's because they don't inline functions as aggressively
> as gcc does.
>
>> --- a/xen/Rules.mk
>> +++ b/xen/Rules.mk
>> @@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
>>  CFLAGS += -nostdinc -fno-builtin -fno-common
>>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
>> -CFLAGS += -Wa,--strip-local-absolute
>>  CFLAGS += '-D__OBJECT_FILE__="$@"'
>>  
>> +ifneq ($(clang),y)
>> +# Clang doesn't understand this command line argument, and doesn't appear to
>> +# have an suitable alternative.  The resulting compiled binary does function,
>> +# but has an excessively large symbol table.
>> +CFLAGS += -Wa,--strip-local-absolute
>> +endif
> Well, that's the brute force undo-it-altogether-for-clang approach
> that I think Doug had also considered. You may have seen the
> discussion (on irc iirc) - I'd really like to see the option still getting
> passed to gas (for all the .S files) even when using clang. Would
> that really be hard to arrange for?

That won't fix the fact that all the .c files which include
cpufeatureset.h also gets the absolute symbols, to allow the
alternatives() blocks to compile.

It will complicate the clang build quite a bit, and won't make much of a
dent on the symbol table bloat.

~Andrew

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Re: [PATCH for-4.7] xen/build: Fix build with Clang

[Jan Beulich]

>>> On 07.04.16 at 21:16, <andrew.cooper3@citrix.com> wrote:
> On 07/04/16 20:12, Jan Beulich wrote:
>>>>> On 07.04.16 at 20:46, <andrew.cooper3@citrix.com> wrote:
>>> --- a/xen/Rules.mk
>>> +++ b/xen/Rules.mk
>>> @@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
>>>  CFLAGS += -nostdinc -fno-builtin -fno-common
>>>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>>>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
>>> -CFLAGS += -Wa,--strip-local-absolute
>>>  CFLAGS += '-D__OBJECT_FILE__="$@"'
>>>  
>>> +ifneq ($(clang),y)
>>> +# Clang doesn't understand this command line argument, and doesn't appear to
>>> +# have an suitable alternative.  The resulting compiled binary does function,
>>> +# but has an excessively large symbol table.
>>> +CFLAGS += -Wa,--strip-local-absolute
>>> +endif
>> Well, that's the brute force undo-it-altogether-for-clang approach
>> that I think Doug had also considered. You may have seen the
>> discussion (on irc iirc) - I'd really like to see the option still getting
>> passed to gas (for all the .S files) even when using clang. Would
>> that really be hard to arrange for?
> 
> That won't fix the fact that all the .c files which include
> cpufeatureset.h also gets the absolute symbols, to allow the
> alternatives() blocks to compile.

That's understood.

> It will complicate the clang build quite a bit, and won't make much of a
> dent on the symbol table bloat.

While this I'm unclear about: Istr Doug mentioning that simply
adding the option in suitable for to AFLAGS would do.

Jan


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Re: [PATCH for-4.7] xen/build: Fix build with Clang

[Andrew Cooper]

On 07/04/16 20:21, Jan Beulich wrote:
>>>> On 07.04.16 at 21:16, <andrew.cooper3@citrix.com> wrote:
>> On 07/04/16 20:12, Jan Beulich wrote:
>>>>>> On 07.04.16 at 20:46, <andrew.cooper3@citrix.com> wrote:
>>>> --- a/xen/Rules.mk
>>>> +++ b/xen/Rules.mk
>>>> @@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
>>>>  CFLAGS += -nostdinc -fno-builtin -fno-common
>>>>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>>>>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
>>>> -CFLAGS += -Wa,--strip-local-absolute
>>>>  CFLAGS += '-D__OBJECT_FILE__="$@"'
>>>>  
>>>> +ifneq ($(clang),y)
>>>> +# Clang doesn't understand this command line argument, and doesn't appear to
>>>> +# have an suitable alternative.  The resulting compiled binary does function,
>>>> +# but has an excessively large symbol table.
>>>> +CFLAGS += -Wa,--strip-local-absolute
>>>> +endif
>>> Well, that's the brute force undo-it-altogether-for-clang approach
>>> that I think Doug had also considered. You may have seen the
>>> discussion (on irc iirc) - I'd really like to see the option still getting
>>> passed to gas (for all the .S files) even when using clang. Would
>>> that really be hard to arrange for?
>> That won't fix the fact that all the .c files which include
>> cpufeatureset.h also gets the absolute symbols, to allow the
>> alternatives() blocks to compile.
> That's understood.
>
>> It will complicate the clang build quite a bit, and won't make much of a
>> dent on the symbol table bloat.
> While this I'm unclear about: Istr Doug mentioning that simply
> adding the option in suitable for to AFLAGS would do.

In which case I clearly missed that bit on IRC.

I am happy to defer to Doug's solution if it actually resolves the
underlying issue.

~Andrew

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Re: [PATCH for-4.7] xen/build: Fix build with Clang

[Doug Goldstein]

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On 4/7/16 2:21 PM, Jan Beulich wrote:
>>>> On 07.04.16 at 21:16, <andrew.cooper3@citrix.com> wrote:
>> On 07/04/16 20:12, Jan Beulich wrote:
>>>>>> On 07.04.16 at 20:46, <andrew.cooper3@citrix.com> wrote:
>>>> --- a/xen/Rules.mk
>>>> +++ b/xen/Rules.mk
>>>> @@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
>>>>  CFLAGS += -nostdinc -fno-builtin -fno-common
>>>>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>>>>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
>>>> -CFLAGS += -Wa,--strip-local-absolute
>>>>  CFLAGS += '-D__OBJECT_FILE__="$@"'
>>>>  
>>>> +ifneq ($(clang),y)
>>>> +# Clang doesn't understand this command line argument, and doesn't appear to
>>>> +# have an suitable alternative.  The resulting compiled binary does function,
>>>> +# but has an excessively large symbol table.
>>>> +CFLAGS += -Wa,--strip-local-absolute
>>>> +endif
>>> Well, that's the brute force undo-it-altogether-for-clang approach
>>> that I think Doug had also considered. You may have seen the
>>> discussion (on irc iirc) - I'd really like to see the option still getting
>>> passed to gas (for all the .S files) even when using clang. Would
>>> that really be hard to arrange for?
>>
>> That won't fix the fact that all the .c files which include
>> cpufeatureset.h also gets the absolute symbols, to allow the
>> alternatives() blocks to compile.
> 
> That's understood.
> 
>> It will complicate the clang build quite a bit, and won't make much of a
>> dent on the symbol table bloat.
> 
> While this I'm unclear about: Istr Doug mentioning that simply
> adding the option in suitable for to AFLAGS would do.
> 
> Jan
> 

I was trying to do exactly what you mentioned where we still passed it
to gas and didn't pass it to llvm but unfortunately at some point the
flags get combined together and passed to llvm and fails.

-- 
Doug Goldstein


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