Re: Problem building libstdc++ for the avr target

[Jonathan Wakely <jwakely@redhat.com>]

On 10/12/20 18:39 +0100, Vladimir V via Libstdc++ wrote:
>Hello.
>
>Could you please have a look at my trivial patch.
>It works as intended with avr-libc and doesn't seem to introduce
>regressions for x86_64 hosts.

I've pushed this to master now, thanks for the patch.

>What would be your suggestions for testing?
>
>Thank you
>Vladimir
>
>чт, 10 дек. 2020 г. в 00:00, Vladimir V <vv.os.swe@gmail.com>:
>
>> Thank you for the quick response.
>> The patch solves the problem.
>>
>> ср, 9 дек. 2020 г. в 18:01, Jonathan Wakely <jwakely@redhat.com>:
>>
>>> On 09/12/20 12:49 +0000, Jonathan Wakely wrote:
>>> >On 09/12/20 13:32 +0100, Vladimir V wrote:
>>> >>Hello.
>>> >>
>>> >>While testing with the current upstream I encountered a compilation
>>> issue.
>>> >>Although I build with "--disable-threads" flag the following error
>>> occurs:
>>> >>
>>> >>../../../../../libstdc++-v3/src/c++11/thread.cc:39:4: error: #error "No
>>> >>sleep function known for this target"
>>> >>
>>> >>Previously the check was inside the  #ifdef _GLIBCXX_HAS_GTHREADS that
>>> >>prevented the error from happening (in my case with gcc v10.1),
>>> >>So I would like to ask if the thread.cc should be involved in the build
>>> if
>>> >>the threads support is configured to be disabled?
>>> >
>>> >Yes, the file is always built, but which definitions it contains
>>> >depends on what is configured for the target.
>>> >
>>> >The std::this_thread::sleep_for and std::this_thread::sleep_until
>>> >functions don't actually depend on threads at all. They just sleep.
>>> >
>>> >But that still requires target support, just different support from
>>> >threads.
>>> >
>>> >>And if it should, then can the condition be reworked to cover the
>>> described
>>> >>case?
>>> >
>>> >Yes, I'll do that. Thanks for bringing it to my attention.
>>> >
>>> >I assume we can't use avr-libc's delay functions, because they depend
>>> >on the CPU clock frequency, which isn't known when we compile
>>> >libstdc++. So I'll just suppress the declarations of those functions
>>> >and remove the #error.
>>>
>>> The attached patch adds a new _GLIBCXX_NO_SLEEP configure macro which
>>> should get defined for your hosted AVR build. That should mean that
>>> std::this_thread::sleep_for is not defined, and src/c++11/thread.cc
>>> will no longer insist on some way to sleep being supported.
>>>
>>> I've only tested this on powerpc64le-linux, so please let me know if
>>> it works for you.
>>>
>>> Pushed to master.
>>>
>>>
>>>

From fbb2144b56625adf594f8812189b983fa66c910a Mon Sep 17 00:00:00 2001
>From: Vladimir Vishnevsky <vv.os.swe@gmail.com>
>Date: Tue, 8 Dec 2020 21:45:26 +0100
>Subject: [PATCH] Disabling AC_LIBTOOL_DLOPEN check if building with avr-libc
>
>The AC_LIBTOOL_DLOPEN checks were previously disabled for newlib targets.
>The patch applies similar logic to avr-libc based builds.
>
>2020-12-08 Vladimir Vishnevsky <vv.os.swe@gmail.com>
>
>libstdc++-v3/ChangeLog:
>        Disabling AC_LIBTOOL_DLOPEN check if building with avr-libc.
>        * configure.ac: Skip AC_LIBTOOL_DLOPEN check if avr-libc is used.
>        * configure: Regenerate.
>---
> libstdc++-v3/configure.ac | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
>index cbfdf4c6bad..771814110a1 100644
>--- a/libstdc++-v3/configure.ac
>+++ b/libstdc++-v3/configure.ac
>@@ -90,7 +90,7 @@ AC_SYS_LARGEFILE
> GLIBCXX_CONFIGURE
>
> # Libtool setup.
>-if test "x${with_newlib}" != "xyes"; then
>+if test "x${with_newlib}" != "xyes" && test "x${with_avrlibc}" != "xyes"; then
>   AC_LIBTOOL_DLOPEN
> fi
> AM_PROG_LIBTOOL
>-- 
>2.17.1
>