Re: [PATCH v2 3/5] x86/mm: override stored file names for multiply built sources

[George Dunlap <george.dunlap@citrix.com>]

On 26/10/15 14:34, Martin Pohlack wrote:
> On 26.10.2015 12:51, Jan Beulich wrote:
>> To make it possible to tell apart the static symbols therein, use their
>> object file names instead of their source ones.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> v2: Introduce __OBJECT_FILE__.
>>
>> --- a/xen/Rules.mk
>> +++ b/xen/Rules.mk
>> @@ -42,10 +42,10 @@ ALL_OBJS-y               += $(BASEDIR)/x
>>  ALL_OBJS-y               += $(BASEDIR)/arch/$(TARGET_ARCH)/built_in.o
>>  ALL_OBJS-$(x86)          += $(BASEDIR)/crypto/built_in.o
>>  
>> -CFLAGS += -fno-builtin -fno-common
>> +CFLAGS += -nostdinc -fno-builtin -fno-common
>>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
>> -CFLAGS += -nostdinc
>> +CFLAGS += '-D__OBJECT_FILE__="$@"'
>>  
>>  CFLAGS-$(XSM_ENABLE)    += -DXSM_ENABLE
>>  CFLAGS-$(FLASK_ENABLE)  += -DFLASK_ENABLE
>> --- a/xen/arch/x86/mm/guest_walk.c
>> +++ b/xen/arch/x86/mm/guest_walk.c
>> @@ -21,6 +21,9 @@
>>   * along with this program; If not, see <http://www.gnu.org/licenses/>.
>>   */
>>  
>> +/* Allow uniquely identifying static symbols in the 3 generated objects. */
>> +asm(".file \"" __OBJECT_FILE__ "\"");
>> +
> 
> I wonder if using symlinks to the C files and compiling those would be a
> more obvious way to set the file symbol to something unique.

That's an interesting idea.  My initial reactions:

1. Setting up the runes and such to make those links wouldn't be simpler
than the asm()-ery that Jan has here

2. Having random linked files lying around has the potential to cause
other forms of confusion (git needs to know to ignore them; developers
may not realize that editing one edits all the others, &c; even if they
do, they may accidentally open two files in an editor that doesn't
realize they're the same file, &c)

 -George