[PATCH] Define GEN_AS_CONST_HEADERS when generating header files [BZ #22792]

[H.J. Lu]

On Thu, Feb 22, 2018 at 8:46 AM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 02/22/2018 07:11 AM, Florian Weimer wrote:
>> On 02/21/2018 06:19 PM, H.J. Lu wrote:
>>> On Wed, Feb 21, 2018 at 7:40 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Tue, Feb 20, 2018 at 11:09 PM, Florian Weimer <fweimer@redhat.com> wrote:
>>>>> On 02/08/2018 06:58 PM, H.J. Lu wrote:
>>>>>>
>>>>>>          [BZ #22792]
>>>>>>          * Makerules ($(common-objpfx)%.h): Pass -DGEN_AS_CONST_HEADERS
>>>>>>          to $(CC).
>>>>>>          * sysdeps/unix/sysv/linux/i386/lowlevellock.h: Include
>>>>>>          <tcb-offsets.h> only if GEN_AS_CONST_HEADERS isn't defined.
>>>>>>          * sysdeps/unix/sysv/linux/x86_64/lowlevellock.h: Don't include
>>>>>>          <tcb-offsets.h>.
>>>>>
>>>>>
>>>>> It looks to me that a cleaner fix would be to move the definition of the TCB
>>>>> types to a separate header.
>>>>
>>>> I will take a look.
>>>
>>> sysdeps/i386/nptl/tcb-offsets.sym has
>>>
>>> #include <sysdep.h>
>>> #include <tls.h>
>>> #include <kernel-features.h>
>>>
>>> RESULT offsetof (struct pthread, result)
>>> TID offsetof (struct pthread, tid)
>>> CANCELHANDLING offsetof (struct pthread, cancelhandling)
>>> CLEANUP_JMP_BUF offsetof (struct pthread, cleanup_jmp_buf)
>>> MULTIPLE_THREADS_OFFSET offsetof (tcbhead_t, multiple_threads)
>>> SYSINFO_OFFSET offsetof (tcbhead_t, sysinfo)
>>> CLEANUP offsetof (struct pthread, cleanup)
>>> CLEANUP_PREV offsetof (struct _pthread_cleanup_buffer, __prev)
>>> MUTEX_FUTEX offsetof (pthread_mutex_t, __data.__lock)
>>> POINTER_GUARD offsetof (tcbhead_t, pointer_guard)
>>> #ifndef __ASSUME_PRIVATE_FUTEX
>>> PRIVATE_FUTEX offsetof (tcbhead_t, private_futex)
>>> #endif
>>>
>>> It covers more than just tcbhead_t.  A separate header file for tcbhead_t
>>> won't help here.
>>
>> Yes, it's more involved.
>>
>>>>> The circular dependency is just a cosmetic warning from make, right?
>>>>
>>>> It depends on how unlucky you are.  In one case on a many-core machine
>>>> with make -j60, I had to kill glibc build since it never stopped.
>>
>> If it fixes an actual build issue, then I think your patch is acceptable, although I consider it quite hackish.
>>
>> But please do add a comment explaining the issue before:
>>
>> +# ifndef GEN_AS_CONST_HEADERS
>
> Agreed, I think the hack is OK, but needs a multi-line comment
> explaining *why* the simple route of header disentanglement
> is not easily possible and why this is needed to bootstrap
> the automatic header building without a circular dependency.
>

This is the patch I am checking in.

Thanks.


-- 
H.J.
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