arm-eabi-g++: -isystem option handle header as c linkage

[Kaul, Martin]

Hi,

given the following code:

-- isystem_test.cpp -------------
#include < isystem_test.h>

bool dummy_function( void )
{
return false;
}
-----------------------------------------

-- isystem_test.h ------------------
template <class _CS_cT>
class allocator
{
};
-----------------------------------------

and g++ version: arm-eabi-g++.exe (Linaro GCC 7.2-2017.11)

1. compiling with "arm-eabi-g++ -I . -g -c isystem_test.cpp"
--> OK

2. compiling with " arm-eabi-g++ -isystem . -g -c isystem_test.cpp "
--> output error:
In file included from isystem_test.cpp:3:0:
./isystem_test.h:3:1: error: template with C linkage
template <class _CS_cT>
^~~~~~~~

It seams that the option -isystem changes the include of isystems_test.h into a C include, i.e. the header content seems to be handled as C-Code

Same error behavior with arm-eabi Linaro GCC 6.4-2017.11, Linaro GCC 6.3-2017.05

-----------------
Testing the same with the mingw msys g++ compiler outputs no error:
g++.exe (Rev2, Built by MSYS2 project) 7.2.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
---------------
Also no errors for:
arm-linux-gnueabihf-g++.exe (Linaro GCC 6.3-2017.05)
---------------

Is there a special behavior for arm-eabi g++ compiler?

Best regards
Martin Kaul

[Thomas Preudhomme]

Hi Martin,

In short yes, it is special behavior but I'm not sure that it is intended.
Each target can opt in to *not* have -isystem implicitly wrap headers in
extern C construct. Arm target does not do anything special and thus
inherit that default behavior of implicit extern C, except when targeting
uclinux systems. It seems from [1] that it is this way for legacy reason.

[1] https://gcc.gnu.org/ml/gcc-patches/2012-06/msg01151.html

Best regards,

Thomas

Post by Kaul, Martin
Hi,
-- isystem_test.cpp -------------
#include < isystem_test.h>
bool dummy_function( void )
{
return false;
}
-----------------------------------------
-- isystem_test.h ------------------
template <class _CS_cT>
class allocator
{
};
-----------------------------------------
and g++ version: arm-eabi-g++.exe (Linaro GCC 7.2-2017.11)
1. compiling with "arm-eabi-g++ -I . -g -c isystem_test.cpp"
--> OK
2. compiling with " arm-eabi-g++ -isystem . -g -c isystem_test.cpp "
./isystem_test.h:3:1: error: template with C linkage
template <class _CS_cT>
^~~~~~~~
It seams that the option -isystem changes the include of isystems_test.h
into a C include, i.e. the header content seems to be handled as C-Code
Same error behavior with arm-eabi Linaro GCC 6.4-2017.11, Linaro GCC 6.3-2017.05
-----------------
g++.exe (Rev2, Built by MSYS2 project) 7.2.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
---------------
arm-linux-gnueabihf-g++.exe (Linaro GCC 6.3-2017.05)
---------------
Is there a special behavior for arm-eabi g++ compiler?
Best regards
Martin Kaul
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