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Define GEN_AS_CONST_HEADERS when generating header files [BZ #22792]

Message ID CAMe9rOqV7uaj6dnWtmy7QEDRpC4p+_H0ZxM2Gr1Dg8tw37YE+Q@mail.gmail.com
State New, archived
Headers show

Commit Message

H.J. Lu Feb. 23, 2018, 7:13 p.m. UTC 
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.
diff mbox

Patch

From 55a426ef8c54eb1d6e48b5858eb43496b1742797 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Thu, 8 Feb 2018 08:37:54 -0800
Subject: [PATCH] Define GEN_AS_CONST_HEADERS when generating header files [BZ
 #22792]

Glibc build generates header files to define constants from special .sym
files.  If a .sym file includes the same header file which it generates,
it leads to circular dependency which may lead to build hang on a
many-core machine.  Define GEN_AS_CONST_HEADERS when generating header
files to avoid circular dependency.

<tcb-offsets.h> is needed for i686 and it isn't needed for x86-64 at
least since glibc 2.23.

Tested on i686 and x86-64.

	[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>.
---
 Makerules                                     | 9 ++++++++-
 sysdeps/unix/sysv/linux/i386/lowlevellock.h   | 9 ++++++++-
 sysdeps/unix/sysv/linux/x86_64/lowlevellock.h | 1 -
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/Makerules b/Makerules
index ef6abeac6d..b2c2724fcb 100644
--- a/Makerules
+++ b/Makerules
@@ -276,10 +276,17 @@  ifdef gen-as-const-headers
 # Generating headers for assembly constants.
 # We need this defined early to get into before-compile before
 # it's used in sysd-rules, below.
+# Define GEN_AS_CONST_HEADERS to avoid circular dependency [BZ #22792].
+# NB: <tcb-offsets.h> is generated from tcb-offsets.sym to define
+# offsets and sizes of types in <tls.h> and maybe <pthread.h> which
+# may include <tcb-offsets.h>.  Target header files can check if
+# GEN_AS_CONST_HEADERS is defined to avoid circular dependency which
+# may lead to build hang on a many-core machine.
 $(common-objpfx)%.h $(common-objpfx)%.h.d: $(..)scripts/gen-as-const.awk \
 					   %.sym $(common-before-compile)
 	$(AWK) -f $< $(filter %.sym,$^) \
-	| $(CC) -S -o $(@:.h.d=.h)T3 $(CFLAGS) $(CPPFLAGS) -x c - \
+	| $(CC) -S -o $(@:.h.d=.h)T3 $(CFLAGS) $(CPPFLAGS) \
+		-DGEN_AS_CONST_HEADERS -x c - \
 		-MD -MP -MF $(@:.h=.h.d)T -MT '$(@:.h=.h.d) $(@:.h.d=.h)'
 	sed -n 's/^.*@@@name@@@\([^@]*\)@@@value@@@[^0-9Xxa-fA-F-]*\([0-9Xxa-fA-F-][0-9Xxa-fA-F-]*\).*@@@end@@@.*$$/#define \1 \2/p' \
 		$(@:.h.d=.h)T3 > $(@:.h.d=.h)T
diff --git a/sysdeps/unix/sysv/linux/i386/lowlevellock.h b/sysdeps/unix/sysv/linux/i386/lowlevellock.h
index fb59b57934..38fbc2556f 100644
--- a/sysdeps/unix/sysv/linux/i386/lowlevellock.h
+++ b/sysdeps/unix/sysv/linux/i386/lowlevellock.h
@@ -26,7 +26,14 @@ 
 # include <sys/param.h>
 # include <bits/pthreadtypes.h>
 # include <kernel-features.h>
-# include <tcb-offsets.h>
+/* <tcb-offsets.h> is generated from tcb-offsets.sym to define offsets
+   and sizes of types in <tls.h> as well as <pthread.h> which includes
+   <lowlevellock.h> via nptl/descr.h.  Don't include <tcb-offsets.h>
+   when generating <tcb-offsets.h> to avoid circular dependency which
+   may lead to build hang on a many-core machine.  */
+# ifndef GEN_AS_CONST_HEADERS
+#  include <tcb-offsets.h>
+# endif
 
 # ifndef LOCK_INSTR
 #  ifdef UP
diff --git a/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h b/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
index a8bcfbe4a3..eedb6fc990 100644
--- a/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
+++ b/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
@@ -26,7 +26,6 @@ 
 # include <sys/param.h>
 # include <bits/pthreadtypes.h>
 # include <kernel-features.h>
-# include <tcb-offsets.h>
 
 # ifndef LOCK_INSTR
 #  ifdef UP
-- 
2.14.3