[Bug gdb/32503] New: gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[Bug gdb/32503] New: gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[jeffrey.cliff at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

            Bug ID: 32503
           Summary: gdb: 'construct' has not been declared in
                    'std::allocator<unsigned char>
           Product: gdb
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: jeffrey.cliff at gmail dot com
  Target Milestone: ---

( looks very much like #29715
https://sourceware.org/bugzilla/show_bug.cgi?id=29715 )

OS : pureos byzantium
arch : aarch64
gcc : (Debian 10.2.1-6) 10.2.1 20210110
gdb : weekly 16.0.50.20241226
CXXFLAGS=-std=gnu++20 -Os -march=native    
CFLAGS=-std=gnu17 -Os -march=native    

true "AR_FLAGS=rc" "CC_FOR_BUILD=gcc" "CFLAGS=-std=gnu17 -Os -march=native    "
"CXXFLAGS=-std=gnu++20 -Os -march=native    " "CFLAGS_FOR_BUILD=-std=gnu17 -Os
-march=native" "CFLAGS_FOR_TARGET=-g -O2  -std=gnu17 -Os -march=native"
"INSTALL=/usr/bin/install -c" "INSTALL_DATA=/usr/bin/install -c -m 644"
"INSTALL_PROGRAM=/usr/bin/install -c" "INSTALL_SCRIPT=/usr/bin/install -c"
"LDFLAGS=-s " "LIBCFLAGS=-std=gnu17 -Os -march=native  "
"LIBCFLAGS_FOR_TARGET=-g -O2  -std=gnu17 -Os -march=native" "MAKE=make"
"MAKEINFO=makeinfo --split-size=5000000 --split-size=5000000 " "PICFLAG="
"PICFLAG_FOR_TARGET=" "SHELL=/bin/bash" "EXPECT=expect" "RUNTEST=runtest"
"RUNTESTFLAGS=" "exec_prefix=/usr/local" "infodir=/usr/local/share/info"
"libdir=/usr/local/lib" "prefix=/usr/local"
"tooldir=/usr/local/aarch64-unknown-linux-gnu" "AR=ar --plugin
/usr/lib/gcc/aarch64-linux-gnu/10/liblto_plugin.so" "AS=as" "CC=gcc" "CXX=g++"
"LD=ld" "LIBCFLAGS=-std=gnu17 -Os -march=native  " "NM=nm" "PICFLAG="
"RANLIB=ranlib --plugin /usr/lib/gcc/aarch64-linux-gnu/10/liblto_plugin.so"
"DESTDIR=" DO=all multi-do 

when making :

make[4]: Entering directory '/home/purism/gdb-16.0.50.20241226/gdbsupport'
  CXX      common-utils.o
In file included from ../gdbsupport/def-vector.h:22,
                 from ../gdbsupport/byte-vector.h:21,
                 from ././common-utils.h:25,
                 from ././common-defs.h:206,
                 from <command-line>:
../gdbsupport/default-init-alloc.h: In instantiation of ‘class
gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> >’:
/usr/include/c++/10/bits/stl_vector.h:87:21:   required from ‘struct
std::_Vector_base<unsigned char, gdb::default_init_allocator<unsigned char,
std::allocator<unsigned char> > >’
/usr/include/c++/10/bits/stl_vector.h:389:11:   required from ‘class
std::vector<unsigned char, gdb::default_init_allocator<unsigned char,
std::allocator<unsigned char> > >’
common-utils.cc:459:25:   required from here
../gdbsupport/default-init-alloc.h:63:12: error: ‘construct’ has not been
declared in ‘std::allocator<unsigned char>’
   63 |   using A::construct;
      |            ^~~~~~~~~


this does *not* occur when $CFLAGS / $CXXFLAGS are empty.

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[Bug gdb/32503] gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |ssbssa at sourceware dot org
   Last reconfirmed|                            |2024-12-27

--- Comment #1 from Hannes Domani <ssbssa at sourceware dot org> ---
The fix [1] of PR29715 checks if __cplusplus is at least 202002L to detect
c++20, but in gcc-10 the value used for c++20 is actually 201709L (it's 201703L
for c++17).


[1]
https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=6feae66da1d652a50c1759bae46128087f7dfab0

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[Bug gdb/32503] gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
I wonder if this code could check __cpp_lib_polymorphic_allocator instead.
Maybe that would be more robust.  See
https://en.cppreference.com/w/cpp/feature_test#cpp_lib_polymorphic_allocator

I'm not sure if we want to change the code to check 201709L.
I guess it would be ok if it's harmless for other situations,
at least with a suitable comment.

Anyway a workaround is not to build in C++20 mode.
gdb is officially using C++17 (though in practice it
uses some C++20 things if they are available).

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[Bug build/32503] gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|gdb                         |build
                 CC|                            |vries at gcc dot gnu.org

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[Bug build/32503] gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
https://sourceware.org/pipermail/gdb-patches/2025-January/214512.html

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[Bug build/32503] gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

--- Comment #4 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6f04937e1d7db190ca96ec08d8aeb25f0ec6e994

commit 6f04937e1d7db190ca96ec08d8aeb25f0ec6e994
Author: Tom de Vries <tdevries@suse.de>
Date:   Fri Jan 10 08:40:11 2025 +0100

    [gdb/build, c++20] Fix build with gcc 10

    With gcc 10 and -std=c++20, we run into the same problem as reported in
commit
    6feae66da1d ("[gdb/build, c++20] Handle deprecated
std::allocator::construct").

    The problem was fixed using:
    ...
    -template<typename T, typename A = std::allocator<T>>
    +template<typename T,
    +         typename A
    +#if __cplusplus >= 202002L
    +         = std::pmr::polymorphic_allocator<T>
    +#else
    +         = std::allocator<T>
    +#endif
    +        >
    ...
    but that doesn't work for gcc 10, because it defines __cplusplus
differently:
    ...
     $ echo | g++-10 -E -dD -x c++ - -std=c++20 2>&1 | grep __cplusplus
     #define __cplusplus 201709L
     $ echo | g++-11 -E -dD -x c++ - -std=c++20 2>&1 | grep __cplusplus
     #define __cplusplus 202002L
    ...

    Fix this by using the library feature test macro
    __cpp_lib_polymorphic_allocator [1], which is undefined for c++17 and
defined
    for c++20:
    ...
     $ echo | g++-10 -E -dD -x c++ - -include memory_resource -std=c++17 2>&1 \
       | grep __cpp_lib_polymorphic_allocator
     $ echo | g++-10 -E -dD -x c++ - -include memory_resource -std=c++20 2>&1 \
       | grep __cpp_lib_polymorphic_allocator
     #define __cpp_lib_polymorphic_allocator 201902L
     $
    ...

    A similar problem exists for commit 3173529d7de ("[gdb/guile, c++20] Work
    around Werror=volatile in libguile.h").  Fix this by testing for 201709L
    instead.

    Tested on x86_64-linux, by building gdb with
    {gcc 10, clang 17.0.6} x {-std=c++17, -std=c++20}.

    PR build/32503
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32503

    Approved-By: Tom Tromey <tom@tromey.com>

    [1]
https://en.cppreference.com/w/cpp/feature_test#cpp_lib_polymorphic_allocator

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[Bug build/32503] gdb: 'construct' has not been declared in 'std::allocator<unsigned char>

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=32503

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |17.1

--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
Fixed.

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