gcc sysroot 问题

xuefeihumei

各位，
     我有一个问题，我安装别人的交叉编译工具链时，我仅仅是向/etc/profile中添加了类似
     export PATH="/opt/hisi-linux-nptl/arm-hisiv100-linux/target/binPATH"  这样的一条命令，但是查看arm-hisiv100nptl-linux-gcc -v 得到：

   Using built-in specs.
Target: arm-hisiv100-linux-uclibcgnueabi
Configured with: ../gcc-4.4-2010q1/configure --host=i486-linux-gnu --build=i486-linux-gnu --target=arm-hisiv100-linux-uclibcgnueabi --prefix=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/arm-hisiv100-linux --enable-threads --disable-libmudflap --disable-libssp --disable-libstdcxx-pch --with-arch=armv5te --with-gnu-as --with-gnu-ld --enable-languages=c,c++ --enable-shared --enable-lto --enable-symvers=gnu --enable-__cxa_atexit --disable-nls --enable-extra-hisi-multilibs --with-sysroot=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/arm-hisiv100-linux/target --with-build-sysroot=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/arm-hisiv100-linux/target --with-gmp=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/host_lib --with-mpfr=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/host_lib --with-ppl=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/host_lib --with-cloog=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/host_lib --with-libelf=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/host_lib --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bstatic -lm' --enable-libgomp --enable-poison-system-directories --with-libelf=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/host_lib --with-pkgversion='Hisilicon_v100(gcc4.4-290+uclibc_0.9.32.1+eabi+linuxpthread)' --with-bugurl=http://www.hisilicon.com/cn/service/claim.html
Thread model: posix
gcc version 4.4.1 (Hisilicon_v100(gcc4.4-290+uclibc_0.9.32.1+eabi+linuxpthread))

其中， --with-sysroot=/home/sying/uclibc_h3/hisiv100_finalnptl_src/hisiv100_src/install/arm-hisiv100-linux/target  但是这个目录并不是我的系统目录。
但是，我在使用这个工具链时，是好用的，也就是它找到了正确的sysroot，请问他是怎么做到的？