Re: [Multiple reverts] [RFC PATCH] build: include/compat: figure out which other compat headers are needed

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.01.2023 08:46, Jan Beulich wrote:
> On 11.01.2023 23:29, Andrew Cooper wrote:
>> For posterity,
>> https://gitlab.com/xen-project/people/andyhhp/xen/-/jobs/3585379553 is
>> the issue in question.
>>
>> In file included from arch/x86/hvm/hvm.c:82:
>> ./include/compat/hvm/hvm_op.h:6:10: fatal error: ../trace.h: No such
>> file or directory
>>     6 | #include "../trace.h"
>>       |          ^~~~~~~~~~~~
>> compilation terminated.
>> make[4]: *** [Rules.mk:246: arch/x86/hvm/hvm.o] Error 1
>> make[3]: *** [Rules.mk:320: arch/x86/hvm] Error 2
>> make[3]: *** Waiting for unfinished jobs....
>>
>>
>> All public headers use "../" relative includes for traversing the
>> public/ hierarchy.  This cannot feasibly change given our "copy this
>> into your project" stance, but it means the compat headers have the same
>> structure under compat/.
>>
>> This include is supposed to be including compat/trace.h but it was
>> actually picking up x86's asm/trace.h, hence the build failure now that
>> I've deleted the file.
>>
>> This demonstrates that trying to be clever with -iquote is a mistake. 
>> Nothing good can possibly come of having the <> and "" include paths
>> being different.  Therefore we must revert all uses of -iquote.
> 
> I'm afraid I can't see the connection between use of -iquote and the bug
> here.

In fact I think the issue was caused by

CFLAGS += -I$(srctree)/arch/x86/include/asm/mach-generic
CFLAGS += -I$(srctree)/arch/x86/include/asm/mach-default

which allowed the compiler when seeing "../trace.h" to pick up
arch/x86/include/asm/trace.h. No -iquote in sight here; all that
happens is that #include "..." fall back to using -I specified
paths when the file could not be found by using ""-only paths.

Jan