* [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
@ 2021-09-08 12:15 Tom de Vries
2021-09-20 23:04 ` [PING][PATCH, " Tom de Vries
2021-09-23 14:27 ` [PATCH, " Simon Marchi
0 siblings, 2 replies; 7+ messages in thread
From: Tom de Vries @ 2021-09-08 12:15 UTC (permalink / raw)
To: gdb-patches
Hi,
The problem reported in PR28318 is that when using a gcc version that (while
supporting c++11) does not support c++11 by default, the configure test for
std::thread support will fail.
If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
have:
...
CXX="g++ -std=gnu++11"
...
and the test for std::thread support would succeed.
Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
which does:
...
CXX=g++
CXX_DIALECT=-std=gnu++11
...
We could add $CXX_DIALECT to the test for std::thread support, but that would
have to be repeated for each added c++ support test.
Instead, fix this by doing:
...
CXX="g++ -std=gnu++11"
CXX_DIALECT=-std=gnu++11
...
The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
AX_CXX_COMPILE_STDCXX from autoconf.
Tested on x86_64-linux.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28318
Any comments?
Thanks,
- Tom
[gdb/build] Add CXX_DIALECT to CXX
---
gdb/ax_cxx_compile_stdcxx.m4 | 8 ++++++++
gdb/configure | 8 ++++++++
gdbserver/configure | 8 ++++++++
gdbsupport/configure | 8 ++++++++
4 files changed, 32 insertions(+)
diff --git a/gdb/ax_cxx_compile_stdcxx.m4 b/gdb/ax_cxx_compile_stdcxx.m4
index 413755a2e88..29d8e10bcc4 100644
--- a/gdb/ax_cxx_compile_stdcxx.m4
+++ b/gdb/ax_cxx_compile_stdcxx.m4
@@ -94,6 +94,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
CXX="$ac_save_CXX"])
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -118,6 +122,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
CXX="$ac_save_CXX"])
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
diff --git a/gdb/configure b/gdb/configure
index f0b1af4a6ea..98badb46cfd 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -5841,6 +5841,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -6160,6 +6164,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
diff --git a/gdbserver/configure b/gdbserver/configure
index b227167e270..f05c1a9b976 100755
--- a/gdbserver/configure
+++ b/gdbserver/configure
@@ -5625,6 +5625,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -5944,6 +5948,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
diff --git a/gdbsupport/configure b/gdbsupport/configure
index a9dd02c5b72..ae6047865ae 100755
--- a/gdbsupport/configure
+++ b/gdbsupport/configure
@@ -6520,6 +6520,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -6839,6 +6843,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PING][PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
2021-09-08 12:15 [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX Tom de Vries
@ 2021-09-20 23:04 ` Tom de Vries
2021-09-23 14:27 ` [PATCH, " Simon Marchi
1 sibling, 0 replies; 7+ messages in thread
From: Tom de Vries @ 2021-09-20 23:04 UTC (permalink / raw)
To: gdb-patches
On 9/8/21 2:15 PM, Tom de Vries wrote:
> Hi,
>
> The problem reported in PR28318 is that when using a gcc version that (while
> supporting c++11) does not support c++11 by default, the configure test for
> std::thread support will fail.
>
> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
> have:
> ...
> CXX="g++ -std=gnu++11"
> ...
> and the test for std::thread support would succeed.
>
> Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
> which does:
> ...
> CXX=g++
> CXX_DIALECT=-std=gnu++11
> ...
>
> We could add $CXX_DIALECT to the test for std::thread support, but that would
> have to be repeated for each added c++ support test.
>
> Instead, fix this by doing:
> ...
> CXX="g++ -std=gnu++11"
> CXX_DIALECT=-std=gnu++11
> ...
>
> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
> AX_CXX_COMPILE_STDCXX from autoconf.
>
> Tested on x86_64-linux.
>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28318
>
> Any comments?
>
Ping.
Thanks,
- Tom
> [gdb/build] Add CXX_DIALECT to CXX
>
> ---
> gdb/ax_cxx_compile_stdcxx.m4 | 8 ++++++++
> gdb/configure | 8 ++++++++
> gdbserver/configure | 8 ++++++++
> gdbsupport/configure | 8 ++++++++
> 4 files changed, 32 insertions(+)
>
> diff --git a/gdb/ax_cxx_compile_stdcxx.m4 b/gdb/ax_cxx_compile_stdcxx.m4
> index 413755a2e88..29d8e10bcc4 100644
> --- a/gdb/ax_cxx_compile_stdcxx.m4
> +++ b/gdb/ax_cxx_compile_stdcxx.m4
> @@ -94,6 +94,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
> CXX="$ac_save_CXX"])
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -118,6 +122,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
> CXX="$ac_save_CXX"])
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> diff --git a/gdb/configure b/gdb/configure
> index f0b1af4a6ea..98badb46cfd 100755
> --- a/gdb/configure
> +++ b/gdb/configure
> @@ -5841,6 +5841,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -6160,6 +6164,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> diff --git a/gdbserver/configure b/gdbserver/configure
> index b227167e270..f05c1a9b976 100755
> --- a/gdbserver/configure
> +++ b/gdbserver/configure
> @@ -5625,6 +5625,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -5944,6 +5948,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> diff --git a/gdbsupport/configure b/gdbsupport/configure
> index a9dd02c5b72..ae6047865ae 100755
> --- a/gdbsupport/configure
> +++ b/gdbsupport/configure
> @@ -6520,6 +6520,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -6839,6 +6843,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
2021-09-08 12:15 [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX Tom de Vries
2021-09-20 23:04 ` [PING][PATCH, " Tom de Vries
@ 2021-09-23 14:27 ` Simon Marchi
2021-09-23 14:33 ` Pedro Alves
2021-09-27 12:59 ` Tom de Vries
1 sibling, 2 replies; 7+ messages in thread
From: Simon Marchi @ 2021-09-23 14:27 UTC (permalink / raw)
To: Tom de Vries, gdb-patches
On 2021-09-08 8:15 a.m., Tom de Vries wrote:
> Hi,
>
> The problem reported in PR28318 is that when using a gcc version that (while
> supporting c++11) does not support c++11 by default, the configure test for
> std::thread support will fail.
>
> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
> have:
> ...
> CXX="g++ -std=gnu++11"
> ...
> and the test for std::thread support would succeed.
>
> Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
> which does:
> ...
> CXX=g++
> CXX_DIALECT=-std=gnu++11
> ...
>
> We could add $CXX_DIALECT to the test for std::thread support, but that would
> have to be repeated for each added c++ support test.
>
> Instead, fix this by doing:
> ...
> CXX="g++ -std=gnu++11"
> CXX_DIALECT=-std=gnu++11
> ...
>
> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
> AX_CXX_COMPILE_STDCXX from autoconf.
From autoconf-archive?
At first glance, it looks like CXX_DIALECT would not be needed anymore,
since it's only used to be appended to CXX in Makefiles. So now it
would end up twice in the command-line, which is not harmful but not
useful.
However, if we look at the original explanation of why we have this
local modification:
We need to tweak AX_CXX_COMPILE_STDCXX a bit though. Pristine
upstream AX_CXX_COMPILE_STDCXX appends -std=gnu++11 to CXX directly.
That doesn't work for us, because the top level Makefile passes CXX
down to subdirs, and that overrides whatever gdb/Makefile may set CXX
to. The result would be that a make invocation from the build/gdb/
directory would use "g++ -std=gnu++11" as expected, while a make
invocation at the top level would not.
So instead of having AX_CXX_COMPILE_STDCXX set CXX directly, tweak it
to AC_SUBST a separate variable -- CXX_DIALECT -- and use '$(CXX)
(CXX_DIALECT)' to compile/link.
https://gitlab.com/gnutools/binutils-gdb/-/commit/0bcda68539948828795564b35a497dc69c27f768
So it sounds like we need both (and your patch is correct):
- the switch in CXX for the std::thread tests (and other tests)
- the switch in CXX_DIALECT so it can be appended in Makefiles, to
counteract the fact that the top-level Makefile overrides CXX
This should probably be explained in the comment, because that situation
is strange, and people might wonder why we end up with two -std=...
switches, and might try to "fix" it.
Simon
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
2021-09-23 14:27 ` [PATCH, " Simon Marchi
@ 2021-09-23 14:33 ` Pedro Alves
2021-09-27 12:59 ` Tom de Vries
1 sibling, 0 replies; 7+ messages in thread
From: Pedro Alves @ 2021-09-23 14:33 UTC (permalink / raw)
To: Simon Marchi, Tom de Vries, gdb-patches
On 2021-09-23 3:27 p.m., Simon Marchi wrote:
>
>
> On 2021-09-08 8:15 a.m., Tom de Vries wrote:
>> Hi,
>>
>> The problem reported in PR28318 is that when using a gcc version that (while
>> supporting c++11) does not support c++11 by default, the configure test for
>> std::thread support will fail.
>>
>> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
>> have:
>> ...
>> CXX="g++ -std=gnu++11"
>> ...
>> and the test for std::thread support would succeed.
>>
>> Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
>> which does:
>> ...
>> CXX=g++
>> CXX_DIALECT=-std=gnu++11
>> ...
>>
>> We could add $CXX_DIALECT to the test for std::thread support, but that would
>> have to be repeated for each added c++ support test.
>>
>> Instead, fix this by doing:
>> ...
>> CXX="g++ -std=gnu++11"
>> CXX_DIALECT=-std=gnu++11
>> ...
>>
>> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
>> AX_CXX_COMPILE_STDCXX from autoconf.
>
> From autoconf-archive?
>
> At first glance, it looks like CXX_DIALECT would not be needed anymore,
> since it's only used to be appended to CXX in Makefiles. So now it
> would end up twice in the command-line, which is not harmful but not
> useful.
>
> However, if we look at the original explanation of why we have this
> local modification:
>
> We need to tweak AX_CXX_COMPILE_STDCXX a bit though. Pristine
> upstream AX_CXX_COMPILE_STDCXX appends -std=gnu++11 to CXX directly.
> That doesn't work for us, because the top level Makefile passes CXX
> down to subdirs, and that overrides whatever gdb/Makefile may set CXX
> to. The result would be that a make invocation from the build/gdb/
> directory would use "g++ -std=gnu++11" as expected, while a make
> invocation at the top level would not.
>
> So instead of having AX_CXX_COMPILE_STDCXX set CXX directly, tweak it
> to AC_SUBST a separate variable -- CXX_DIALECT -- and use '$(CXX)
> (CXX_DIALECT)' to compile/link.
>
> https://gitlab.com/gnutools/binutils-gdb/-/commit/0bcda68539948828795564b35a497dc69c27f768
>
> So it sounds like we need both (and your patch is correct):
>
> - the switch in CXX for the std::thread tests (and other tests)
> - the switch in CXX_DIALECT so it can be appended in Makefiles, to
> counteract the fact that the top-level Makefile overrides CXX
Thanks for raising this aspect. I had been meaning to reply raising it, and ask
where that original motivation is still a concern, as it wasn't clear
from the patch description.
Pedro Alves
>
> This should probably be explained in the comment, because that situation
> is strange, and people might wonder why we end up with two -std=...
> switches, and might try to "fix" it.
>
> Simon
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
2021-09-23 14:27 ` [PATCH, " Simon Marchi
2021-09-23 14:33 ` Pedro Alves
@ 2021-09-27 12:59 ` Tom de Vries
2021-10-04 13:58 ` Tom de Vries
1 sibling, 1 reply; 7+ messages in thread
From: Tom de Vries @ 2021-09-27 12:59 UTC (permalink / raw)
To: Simon Marchi, gdb-patches
[-- Attachment #1: Type: text/plain, Size: 2705 bytes --]
On 9/23/21 4:27 PM, Simon Marchi wrote:
>
>
> On 2021-09-08 8:15 a.m., Tom de Vries wrote:
>> Hi,
>>
>> The problem reported in PR28318 is that when using a gcc version that (while
>> supporting c++11) does not support c++11 by default, the configure test for
>> std::thread support will fail.
>>
>> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
>> have:
>> ...
>> CXX="g++ -std=gnu++11"
>> ...
>> and the test for std::thread support would succeed.
>>
>> Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
>> which does:
>> ...
>> CXX=g++
>> CXX_DIALECT=-std=gnu++11
>> ...
>>
>> We could add $CXX_DIALECT to the test for std::thread support, but that would
>> have to be repeated for each added c++ support test.
>>
>> Instead, fix this by doing:
>> ...
>> CXX="g++ -std=gnu++11"
>> CXX_DIALECT=-std=gnu++11
>> ...
>>
>> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
>> AX_CXX_COMPILE_STDCXX from autoconf.
>
> From autoconf-archive?
>
Yes, updated.
> At first glance, it looks like CXX_DIALECT would not be needed anymore,
> since it's only used to be appended to CXX in Makefiles. So now it
> would end up twice in the command-line, which is not harmful but not
> useful.
>
> However, if we look at the original explanation of why we have this
> local modification:
>
> We need to tweak AX_CXX_COMPILE_STDCXX a bit though. Pristine
> upstream AX_CXX_COMPILE_STDCXX appends -std=gnu++11 to CXX directly.
> That doesn't work for us, because the top level Makefile passes CXX
> down to subdirs, and that overrides whatever gdb/Makefile may set CXX
> to. The result would be that a make invocation from the build/gdb/
> directory would use "g++ -std=gnu++11" as expected, while a make
> invocation at the top level would not.
>
> So instead of having AX_CXX_COMPILE_STDCXX set CXX directly, tweak it
> to AC_SUBST a separate variable -- CXX_DIALECT -- and use '$(CXX)
> (CXX_DIALECT)' to compile/link.
>
> https://gitlab.com/gnutools/binutils-gdb/-/commit/0bcda68539948828795564b35a497dc69c27f768
>
> So it sounds like we need both (and your patch is correct):
>
> - the switch in CXX for the std::thread tests (and other tests)
> - the switch in CXX_DIALECT so it can be appended in Makefiles, to
> counteract the fact that the top-level Makefile overrides CXX
>
> This should probably be explained in the comment, because that situation
> is strange, and people might wonder why we end up with two -std=...
> switches, and might try to "fix" it.
Ack, I've rewritten the commit log to make this more clear (and copied
part of you comments).
Any further comments?
Thanks,
- Tom
[-- Attachment #2: 0001-gdb-build-Add-CXX_DIALECT-to-CXX.patch --]
[-- Type: text/x-patch, Size: 5242 bytes --]
[gdb/build] Add CXX_DIALECT to CXX
Say we use a gcc version that (while supporting c++11) does not support c++11
by default, and needs an -std setting to enable it.
If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf-archive, then
we'd have:
...
CXX="g++ -std=gnu++11"
...
That mechanism however has the following problem (quoting from commit
0bcda685399):
...
the top level Makefile passes CXX down to subdirs, and that overrides whatever
gdb/Makefile may set CXX to. The result would be that a make invocation from
the build/gdb/ directory would use "g++ -std=gnu++11" as expected, while a
make invocation at the top level would not.
...
Commit 0bcda685399 fixes this by using a custom AX_CXX_COMPILE_STDCXX which
does:
...
CXX=g++
CXX_DIALECT=-std=gnu++11
...
The problem reported in PR28318 is that using the custom instead of the
default AX_CXX_COMPILE_STDCXX makes the configure test for std::thread
support fail.
We could simply add $CXX_DIALECT to the test for std::thread support, but
that would have to be repeated for each added c++ support test.
Instead, fix this by doing:
...
CXX="g++ -std=gnu++11"
CXX_DIALECT=-std=gnu++11
...
This is somewhat awkward, since it results in -std=gnu++11 occuring twice in
some situations:
...
$ touch src/gdb/dwarf2/read.c
$ ( cd build/gdb; make V=1 dwarf2/read.o )
g++-4.8 -std=gnu++11 -x c++ -std=gnu++11 ...
...
However, both settings are needed:
- the switch in CXX for the std::thread tests (and other tests)
- the switch in CXX_DIALECT so it can be appended in Makefiles, to
counteract the fact that the top-level Makefile overrides CXX
The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
AX_CXX_COMPILE_STDCXX from autoconf-archive.
Tested on x86_64-linux.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28318
---
gdb/ax_cxx_compile_stdcxx.m4 | 8 ++++++++
gdb/configure | 8 ++++++++
gdbserver/configure | 8 ++++++++
gdbsupport/configure | 8 ++++++++
4 files changed, 32 insertions(+)
diff --git a/gdb/ax_cxx_compile_stdcxx.m4 b/gdb/ax_cxx_compile_stdcxx.m4
index 413755a2e88..29d8e10bcc4 100644
--- a/gdb/ax_cxx_compile_stdcxx.m4
+++ b/gdb/ax_cxx_compile_stdcxx.m4
@@ -94,6 +94,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
CXX="$ac_save_CXX"])
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -118,6 +122,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
CXX="$ac_save_CXX"])
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
diff --git a/gdb/configure b/gdb/configure
index f0b1af4a6ea..98badb46cfd 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -5841,6 +5841,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -6160,6 +6164,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
diff --git a/gdbserver/configure b/gdbserver/configure
index b227167e270..f05c1a9b976 100755
--- a/gdbserver/configure
+++ b/gdbserver/configure
@@ -5625,6 +5625,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -5944,6 +5948,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
diff --git a/gdbsupport/configure b/gdbsupport/configure
index a9dd02c5b72..ae6047865ae 100755
--- a/gdbsupport/configure
+++ b/gdbsupport/configure
@@ -6520,6 +6520,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
@@ -6839,6 +6843,10 @@ eval ac_res=\$$cachevar
$as_echo "$ac_res" >&6; }
if eval test x\$$cachevar = xyes; then
CXX_DIALECT="$switch"
+ CXX="$CXX $switch"
+ if test -n "$CXXCPP" ; then
+ CXXCPP="$CXXCPP $switch"
+ fi
ac_success=yes
break
fi
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
2021-09-27 12:59 ` Tom de Vries
@ 2021-10-04 13:58 ` Tom de Vries
2021-10-04 16:16 ` Simon Marchi
0 siblings, 1 reply; 7+ messages in thread
From: Tom de Vries @ 2021-10-04 13:58 UTC (permalink / raw)
To: Simon Marchi, gdb-patches
On 9/27/21 2:59 PM, Tom de Vries via Gdb-patches wrote:
> On 9/23/21 4:27 PM, Simon Marchi wrote:
>>
>> On 2021-09-08 8:15 a.m., Tom de Vries wrote:
>>> Hi,
>>>
>>> The problem reported in PR28318 is that when using a gcc version that (while
>>> supporting c++11) does not support c++11 by default, the configure test for
>>> std::thread support will fail.
>>>
>>> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
>>> have:
>>> ...
>>> CXX="g++ -std=gnu++11"
>>> ...
>>> and the test for std::thread support would succeed.
>>>
>>> Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
>>> which does:
>>> ...
>>> CXX=g++
>>> CXX_DIALECT=-std=gnu++11
>>> ...
>>>
>>> We could add $CXX_DIALECT to the test for std::thread support, but that would
>>> have to be repeated for each added c++ support test.
>>>
>>> Instead, fix this by doing:
>>> ...
>>> CXX="g++ -std=gnu++11"
>>> CXX_DIALECT=-std=gnu++11
>>> ...
>>>
>>> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
>>> AX_CXX_COMPILE_STDCXX from autoconf.
>> From autoconf-archive?
>>
> Yes, updated.
>
>> At first glance, it looks like CXX_DIALECT would not be needed anymore,
>> since it's only used to be appended to CXX in Makefiles. So now it
>> would end up twice in the command-line, which is not harmful but not
>> useful.
>>
>> However, if we look at the original explanation of why we have this
>> local modification:
>>
>> We need to tweak AX_CXX_COMPILE_STDCXX a bit though. Pristine
>> upstream AX_CXX_COMPILE_STDCXX appends -std=gnu++11 to CXX directly.
>> That doesn't work for us, because the top level Makefile passes CXX
>> down to subdirs, and that overrides whatever gdb/Makefile may set CXX
>> to. The result would be that a make invocation from the build/gdb/
>> directory would use "g++ -std=gnu++11" as expected, while a make
>> invocation at the top level would not.
>>
>> So instead of having AX_CXX_COMPILE_STDCXX set CXX directly, tweak it
>> to AC_SUBST a separate variable -- CXX_DIALECT -- and use '$(CXX)
>> (CXX_DIALECT)' to compile/link.
>>
>> https://gitlab.com/gnutools/binutils-gdb/-/commit/0bcda68539948828795564b35a497dc69c27f768
>>
>> So it sounds like we need both (and your patch is correct):
>>
>> - the switch in CXX for the std::thread tests (and other tests)
>> - the switch in CXX_DIALECT so it can be appended in Makefiles, to
>> counteract the fact that the top-level Makefile overrides CXX
>>
>> This should probably be explained in the comment, because that situation
>> is strange, and people might wonder why we end up with two -std=...
>> switches, and might try to "fix" it.
> Ack, I've rewritten the commit log to make this more clear (and copied
> part of you comments).
>
> Any further comments?
>
I'll commit this tomorrow, unless there are further comments.
Thanks,
- Tom
> 0001-gdb-build-Add-CXX_DIALECT-to-CXX.patch
>
> [gdb/build] Add CXX_DIALECT to CXX
>
> Say we use a gcc version that (while supporting c++11) does not support c++11
> by default, and needs an -std setting to enable it.
>
> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf-archive, then
> we'd have:
> ...
> CXX="g++ -std=gnu++11"
> ...
>
> That mechanism however has the following problem (quoting from commit
> 0bcda685399):
> ...
> the top level Makefile passes CXX down to subdirs, and that overrides whatever
> gdb/Makefile may set CXX to. The result would be that a make invocation from
> the build/gdb/ directory would use "g++ -std=gnu++11" as expected, while a
> make invocation at the top level would not.
> ...
>
> Commit 0bcda685399 fixes this by using a custom AX_CXX_COMPILE_STDCXX which
> does:
> ...
> CXX=g++
> CXX_DIALECT=-std=gnu++11
> ...
>
> The problem reported in PR28318 is that using the custom instead of the
> default AX_CXX_COMPILE_STDCXX makes the configure test for std::thread
> support fail.
>
> We could simply add $CXX_DIALECT to the test for std::thread support, but
> that would have to be repeated for each added c++ support test.
>
> Instead, fix this by doing:
> ...
> CXX="g++ -std=gnu++11"
> CXX_DIALECT=-std=gnu++11
> ...
>
> This is somewhat awkward, since it results in -std=gnu++11 occuring twice in
> some situations:
> ...
> $ touch src/gdb/dwarf2/read.c
> $ ( cd build/gdb; make V=1 dwarf2/read.o )
> g++-4.8 -std=gnu++11 -x c++ -std=gnu++11 ...
> ...
>
> However, both settings are needed:
> - the switch in CXX for the std::thread tests (and other tests)
> - the switch in CXX_DIALECT so it can be appended in Makefiles, to
> counteract the fact that the top-level Makefile overrides CXX
>
> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
> AX_CXX_COMPILE_STDCXX from autoconf-archive.
>
> Tested on x86_64-linux.
>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28318
>
> ---
> gdb/ax_cxx_compile_stdcxx.m4 | 8 ++++++++
> gdb/configure | 8 ++++++++
> gdbserver/configure | 8 ++++++++
> gdbsupport/configure | 8 ++++++++
> 4 files changed, 32 insertions(+)
>
> diff --git a/gdb/ax_cxx_compile_stdcxx.m4 b/gdb/ax_cxx_compile_stdcxx.m4
> index 413755a2e88..29d8e10bcc4 100644
> --- a/gdb/ax_cxx_compile_stdcxx.m4
> +++ b/gdb/ax_cxx_compile_stdcxx.m4
> @@ -94,6 +94,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
> CXX="$ac_save_CXX"])
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -118,6 +122,10 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
> CXX="$ac_save_CXX"])
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> diff --git a/gdb/configure b/gdb/configure
> index f0b1af4a6ea..98badb46cfd 100755
> --- a/gdb/configure
> +++ b/gdb/configure
> @@ -5841,6 +5841,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -6160,6 +6164,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> diff --git a/gdbserver/configure b/gdbserver/configure
> index b227167e270..f05c1a9b976 100755
> --- a/gdbserver/configure
> +++ b/gdbserver/configure
> @@ -5625,6 +5625,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -5944,6 +5948,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> diff --git a/gdbsupport/configure b/gdbsupport/configure
> index a9dd02c5b72..ae6047865ae 100755
> --- a/gdbsupport/configure
> +++ b/gdbsupport/configure
> @@ -6520,6 +6520,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
> @@ -6839,6 +6843,10 @@ eval ac_res=\$$cachevar
> $as_echo "$ac_res" >&6; }
> if eval test x\$$cachevar = xyes; then
> CXX_DIALECT="$switch"
> + CXX="$CXX $switch"
> + if test -n "$CXXCPP" ; then
> + CXXCPP="$CXXCPP $switch"
> + fi
> ac_success=yes
> break
> fi
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX
2021-10-04 13:58 ` Tom de Vries
@ 2021-10-04 16:16 ` Simon Marchi
0 siblings, 0 replies; 7+ messages in thread
From: Simon Marchi @ 2021-10-04 16:16 UTC (permalink / raw)
To: Tom de Vries, gdb-patches
On 2021-10-04 09:58, Tom de Vries wrote:
> On 9/27/21 2:59 PM, Tom de Vries via Gdb-patches wrote:
>> On 9/23/21 4:27 PM, Simon Marchi wrote:
>>>
>>> On 2021-09-08 8:15 a.m., Tom de Vries wrote:
>>>> Hi,
>>>>
>>>> The problem reported in PR28318 is that when using a gcc version that (while
>>>> supporting c++11) does not support c++11 by default, the configure test for
>>>> std::thread support will fail.
>>>>
>>>> If gdb would use the default AX_CXX_COMPILE_STDCXX from autoconf, then we'd
>>>> have:
>>>> ...
>>>> CXX="g++ -std=gnu++11"
>>>> ...
>>>> and the test for std::thread support would succeed.
>>>>
>>>> Instead, gdb uses a custom AX_CXX_COMPILE_STDCXX (see commit 0bcda685399)
>>>> which does:
>>>> ...
>>>> CXX=g++
>>>> CXX_DIALECT=-std=gnu++11
>>>> ...
>>>>
>>>> We could add $CXX_DIALECT to the test for std::thread support, but that would
>>>> have to be repeated for each added c++ support test.
>>>>
>>>> Instead, fix this by doing:
>>>> ...
>>>> CXX="g++ -std=gnu++11"
>>>> CXX_DIALECT=-std=gnu++11
>>>> ...
>>>>
>>>> The code added in gdb/ax_cxx_compile_stdcxx.m4 is copied from the default
>>>> AX_CXX_COMPILE_STDCXX from autoconf.
>>> From autoconf-archive?
>>>
>> Yes, updated.
>>
>>> At first glance, it looks like CXX_DIALECT would not be needed anymore,
>>> since it's only used to be appended to CXX in Makefiles. So now it
>>> would end up twice in the command-line, which is not harmful but not
>>> useful.
>>>
>>> However, if we look at the original explanation of why we have this
>>> local modification:
>>>
>>> We need to tweak AX_CXX_COMPILE_STDCXX a bit though. Pristine
>>> upstream AX_CXX_COMPILE_STDCXX appends -std=gnu++11 to CXX directly.
>>> That doesn't work for us, because the top level Makefile passes CXX
>>> down to subdirs, and that overrides whatever gdb/Makefile may set CXX
>>> to. The result would be that a make invocation from the build/gdb/
>>> directory would use "g++ -std=gnu++11" as expected, while a make
>>> invocation at the top level would not.
>>>
>>> So instead of having AX_CXX_COMPILE_STDCXX set CXX directly, tweak it
>>> to AC_SUBST a separate variable -- CXX_DIALECT -- and use '$(CXX)
>>> (CXX_DIALECT)' to compile/link.
>>>
>>> https://gitlab.com/gnutools/binutils-gdb/-/commit/0bcda68539948828795564b35a497dc69c27f768
>>>
>>> So it sounds like we need both (and your patch is correct):
>>>
>>> - the switch in CXX for the std::thread tests (and other tests)
>>> - the switch in CXX_DIALECT so it can be appended in Makefiles, to
>>> counteract the fact that the top-level Makefile overrides CXX
>>>
>>> This should probably be explained in the comment, because that situation
>>> is strange, and people might wonder why we end up with two -std=...
>>> switches, and might try to "fix" it.
>> Ack, I've rewritten the commit log to make this more clear (and copied
>> part of you comments).
>>
>> Any further comments?
>>
>
> I'll commit this tomorrow, unless there are further comments.
>
> Thanks,
> - Tom
That LGTM, thanks.
Simon
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-10-04 16:16 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-08 12:15 [PATCH, master+11][gdb/build] Add CXX_DIALECT to CXX Tom de Vries
2021-09-20 23:04 ` [PING][PATCH, " Tom de Vries
2021-09-23 14:27 ` [PATCH, " Simon Marchi
2021-09-23 14:33 ` Pedro Alves
2021-09-27 12:59 ` Tom de Vries
2021-10-04 13:58 ` Tom de Vries
2021-10-04 16:16 ` Simon Marchi
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