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...