[yocto] Is "--sysroot" enough for variable rootfs of cross-canadian g++?

[Zhang, Jessica]

Lu, Lianhao wrote:
> Richard Purdie wrote on 2010-12-08:
>> Hi Lianhao,
>> 
>> On Tue, 2010-12-07 at 00:02 -0800, Lu, Lianhao wrote:
>>> I'm wondering whether"-sysroot" is enough for our current design
>>> that the rootfs used by toolchain can be copied by the user to
>>> various locations? I just bumped into a problem when the
>>> cross-canadian g++ complaining: fatal error: iostream: No such file
>>> or direcotory. 
>>> 
>>> I tried to compile the following hello.cpp with with
>>> "mips-poky-linux-g++ --sysroot=<mysysroot> hello.cpp".
>>> 
>>> #include <iostream>
>>> 
>>> using namespace std;
>>> 
>>> void main()
>>> 
>>> {
>>> 
>>>   cout << "Hello World!" << endl;
>>> }
>>> 
>>> 
>>> 
>>> I straced the mips-poky-linux-g++ and found that it
>>> searched"<mysysroot>/usr/include" for file iostream while that file
>>> is actually located at"<mysysroot>/usr/include/c++". The
>>> cross-canadian g ++ seems to be configured with"-
>>> with-gxx-include-dir=/opt/poky/sysroots/mips-poky-linux/usr/include/
>>> c ++", but it seems"-sysroot" option has no effect on the gxx
>>> include search path.
>> 
>> So I'm confused as these two sentences appear to contradict each
>> other. 
>> 
>> """
>> it searched "<mysysroot>/usr/include" for file iostream while that
>> file is actually located at"<mysysroot>/usr/include/c++" """
>> 
>> means it did use <mysysroot> and the --with-sysroot option did
>> something but dropped the c++ part at the end of the path?
>> 
> 
> Exactly. It only searched the /usr/include under the sysroot
> specified by "--sysroot" options, but did not search the
> /usr/include/c++.  

Reading gcc manual, it seems --sysroot will only look at
<sysroot>/usr/include and <sysroot>/usr/lib.  I've also played with
-isysroot, which pretty much the same effect as sysroot.  I can only get the
compilation going by explicitly using -I <mysysroot>/usr/include/c++ -I
<mysysroot>/usr/include/c++/i586-poky-linux options.  And by using strace, I
found the command line options won't override the default header/library
searching sequence of gcc (set by with-gxx-include-dir), which still trying
to search under /opt/poky/i586-poky-linux/usr/include/c++, etc first...
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