* [PATCH] Make cstddef / cstdarg more robust (PR 69881)
@ 2016-02-23 7:15 Bernd Edlinger
2016-02-23 9:42 ` Jonathan Wakely
0 siblings, 1 reply; 6+ messages in thread
From: Bernd Edlinger @ 2016-02-23 7:15 UTC (permalink / raw)
To: gcc-patches, libstdc++; +Cc: Jonathan Wakely
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Hi,
as described in the PR 69881 it happens quite often that cstddef is
called with __need_size_t because we still support gmp-4.3.2 which
is installed by contrib/download_prerequisites. This causes a kind
of undefined behavior. It is just by chance that this does not cause
the gcc-6 boot-strap to fail, but it causes gcc-4.9 bootstrap to fail
when the gcc-6 version of cstddef is around. So it looks like a
regression, because the new cstddef is more fragile than before.
As it looks like, neither c/* nor c_std/* headers will compile without
major bug-fixing first, and they are likely not in use by anybody.
Therefore I think it is best not to touch these at all, because it is
hard to test anything there.
So I propose to undefine all problematic __need_* that may cause
cstddef or cstdarg fail to compile.
Boot-strapped and reg-tested on x86_64-pc-linux-gnu
OK for trunk?
Thanks
Bernd.
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2016-02-23 Bernd Edlinger <bernd.edlinger@hotmail.de>
PR libstdc++/69881
* include/c_global/cstdarg: Undefine __need___va_list.
* include/c_global/cstddef: Undefine all kinds of __need_*.
Index: libstdc++-v3/include/c_global/cstdarg
===================================================================
--- libstdc++-v3/include/c_global/cstdarg (revision 233604)
+++ libstdc++-v3/include/c_global/cstdarg (working copy)
@@ -38,6 +38,7 @@
#pragma GCC system_header
+#undef __need___va_list
#include <bits/c++config.h>
#include <stdarg.h>
Index: libstdc++-v3/include/c_global/cstddef
===================================================================
--- libstdc++-v3/include/c_global/cstddef (revision 233604)
+++ libstdc++-v3/include/c_global/cstddef (working copy)
@@ -41,6 +41,11 @@
#pragma GCC system_header
+#undef __need_wchar_t
+#undef __need_ptrdiff_t
+#undef __need_size_t
+#undef __need_NULL
+#undef __need_wint_t
#include <bits/c++config.h>
#include <stddef.h>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Make cstddef / cstdarg more robust (PR 69881)
2016-02-23 7:15 [PATCH] Make cstddef / cstdarg more robust (PR 69881) Bernd Edlinger
@ 2016-02-23 9:42 ` Jonathan Wakely
2016-02-23 10:01 ` Bernd Edlinger
0 siblings, 1 reply; 6+ messages in thread
From: Jonathan Wakely @ 2016-02-23 9:42 UTC (permalink / raw)
To: Bernd Edlinger; +Cc: gcc-patches, libstdc++
On 23/02/16 07:15 +0000, Bernd Edlinger wrote:
>as described in the PR 69881 it happens quite often that cstddef is
>called with __need_size_t because we still support gmp-4.3.2 which
>is installed by contrib/download_prerequisites. This causes a kind
>of undefined behavior. It is just by chance that this does not cause
>the gcc-6 boot-strap to fail, but it causes gcc-4.9 bootstrap to fail
>when the gcc-6 version of cstddef is around. So it looks like a
>regression, because the new cstddef is more fragile than before.
Is it? cstddef hasn't been changed since 2013-06-11. cstdarg hasn't
been changed since 2011-01-30.
What made them more fragile?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Make cstddef / cstdarg more robust (PR 69881)
2016-02-23 9:42 ` Jonathan Wakely
@ 2016-02-23 10:01 ` Bernd Edlinger
2016-02-23 10:09 ` Jakub Jelinek
2016-02-23 10:16 ` Jonathan Wakely
0 siblings, 2 replies; 6+ messages in thread
From: Bernd Edlinger @ 2016-02-23 10:01 UTC (permalink / raw)
To: Jonathan Wakely; +Cc: gcc-patches, libstdc++
On 23/02/15 10:42, Jonathan Wakely wrote:
>On 23/02/16 07:15 +0000, Bernd Edlinger wrote:
>>as described in the PR 69881 it happens quite often that cstddef is
>>called with __need_size_t because we still support gmp-4.3.2 which
>>is installed by contrib/download_prerequisites. This causes a kind
>>of undefined behavior. It is just by chance that this does not cause
>>the gcc-6 boot-strap to fail, but it causes gcc-4.9 bootstrap to fail
>>when the gcc-6 version of cstddef is around. So it looks like a
>>regression, because the new cstddef is more fragile than before.
>
>Is it? cstddef hasn't been changed since 2013-06-11. cstdarg hasn't
>been changed since 2011-01-30.
>
>What made them more fragile?
Good question.
The cstddef had this even in gcc.4.9 that's true, but it was not used
by default:
#if __cplusplus >= 201103L
namespace std
{
// We handle size_t, ptrdiff_t, and nullptr_t in c++config.h.
using ::max_align_t;
}
#endif
Previously the g++ default was --std=gnu++98,
but gcc-6 changed the default to --std=gnu++14.
And when building gcc-4.9, stage1 does not override that with
--std=gnu++98.
That has changed, and that triggers the latent bug.
Bernd.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] Make cstddef / cstdarg more robust (PR 69881)
2016-02-23 10:01 ` Bernd Edlinger
@ 2016-02-23 10:09 ` Jakub Jelinek
2016-02-23 10:20 ` Jonathan Wakely
2016-02-23 10:16 ` Jonathan Wakely
1 sibling, 1 reply; 6+ messages in thread
From: Jakub Jelinek @ 2016-02-23 10:09 UTC (permalink / raw)
To: Bernd Edlinger; +Cc: Jonathan Wakely, gcc-patches, libstdc++
On Tue, Feb 23, 2016 at 10:00:58AM +0000, Bernd Edlinger wrote:
> Previously the g++ default was --std=gnu++98,
> but gcc-6 changed the default to --std=gnu++14.
>
> And when building gcc-4.9, stage1 does not override that with
> --std=gnu++98.
>
> That has changed, and that triggers the latent bug.
So just use -std=gnu++98 in STAGE1_CXXFLAGS or configure with
CXX='g++ -std=gnu++98' if you try to build gcc-4.9 with gcc 6?
I really don't think we should work around this in GCC 6.
Jakub
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Make cstddef / cstdarg more robust (PR 69881)
2016-02-23 10:09 ` Jakub Jelinek
@ 2016-02-23 10:20 ` Jonathan Wakely
0 siblings, 0 replies; 6+ messages in thread
From: Jonathan Wakely @ 2016-02-23 10:20 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: Bernd Edlinger, gcc-patches, libstdc++
On 23/02/16 11:09 +0100, Jakub Jelinek wrote:
>On Tue, Feb 23, 2016 at 10:00:58AM +0000, Bernd Edlinger wrote:
>> Previously the g++ default was --std=gnu++98,
>> but gcc-6 changed the default to --std=gnu++14.
>>
>> And when building gcc-4.9, stage1 does not override that with
>> --std=gnu++98.
>>
>> That has changed, and that triggers the latent bug.
>
>So just use -std=gnu++98 in STAGE1_CXXFLAGS or configure with
>CXX='g++ -std=gnu++98' if you try to build gcc-4.9 with gcc 6?
>
>I really don't think we should work around this in GCC 6.
I agree, but #undefining those macros doesn't hurt, and hopefully the
issue will go away.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Make cstddef / cstdarg more robust (PR 69881)
2016-02-23 10:01 ` Bernd Edlinger
2016-02-23 10:09 ` Jakub Jelinek
@ 2016-02-23 10:16 ` Jonathan Wakely
1 sibling, 0 replies; 6+ messages in thread
From: Jonathan Wakely @ 2016-02-23 10:16 UTC (permalink / raw)
To: Bernd Edlinger; +Cc: gcc-patches, libstdc++
On 23/02/16 10:00 +0000, Bernd Edlinger wrote:
>On 23/02/15 10:42, Jonathan Wakely wrote:
>>On 23/02/16 07:15 +0000, Bernd Edlinger wrote:
>>>as described in the PR 69881 it happens quite often that cstddef is
>>>called with __need_size_t because we still support gmp-4.3.2 which
>>>is installed by contrib/download_prerequisites. This causes a kind
>>>of undefined behavior. It is just by chance that this does not cause
>>>the gcc-6 boot-strap to fail, but it causes gcc-4.9 bootstrap to fail
>>>when the gcc-6 version of cstddef is around. So it looks like a
>>>regression, because the new cstddef is more fragile than before.
>>
>>Is it? cstddef hasn't been changed since 2013-06-11. cstdarg hasn't
>>been changed since 2011-01-30.
>>
>>What made them more fragile?
>
>Good question.
>
>The cstddef had this even in gcc.4.9 that's true, but it was not used
>by default:
>
>#if __cplusplus >= 201103L
>namespace std
>{
> // We handle size_t, ptrdiff_t, and nullptr_t in c++config.h.
> using ::max_align_t;
>}
>#endif
>
>
>Previously the g++ default was --std=gnu++98,
>but gcc-6 changed the default to --std=gnu++14.
Ah yes.
>And when building gcc-4.9, stage1 does not override that with
>--std=gnu++98.
>
>That has changed, and that triggers the latent bug.
Alright then, the patch is OK for trunk.
I might revert it once we stop using the buggy GMP in
contrib/download_prerequisites.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2016-02-23 7:15 [PATCH] Make cstddef / cstdarg more robust (PR 69881) Bernd Edlinger
2016-02-23 9:42 ` Jonathan Wakely
2016-02-23 10:01 ` Bernd Edlinger
2016-02-23 10:09 ` Jakub Jelinek
2016-02-23 10:20 ` Jonathan Wakely
2016-02-23 10:16 ` Jonathan Wakely
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