This error comes out when I use Crosstool-NG toolchain.

I downloaded the file from the following address. Switch to the chroot, compile netperf-2.4.5 failed. The following error:
（http://uclibc.org/downloads/binaries/0.9.30.1/system-image-i686.tar.bz2）

make[3]: Leaving directory `/tmp/netperf-2.4.5/src/missing'
make[3]: Entering directory `/tmp/netperf-2.4.5/src'
if gcc -DHAVE_CONFIG_H -I. -I. -I..     -g -O2 -MT netslot_linux.o -MD -MP -MF ".deps/netslot_linux.Tpo" \
          -c -o netslot_linux.o `test -f 'netslot_linux.c' || echo './'`netslot_linux.c; \
        then mv -f ".deps/netslot_linux.Tpo" ".deps/netslot_linux.Po"; \
        else rm -f ".deps/netslot_linux.Tpo"; exit 1; \
        fi
netslot_linux.c:2:17: error: ftw.h: No such file or directory
netslot_linux.c:13: warning: 'struct FTW' declared inside parameter list
netslot_linux.c:13: warning: its scope is only this definition or declaration, which is probably not what you want
netslot_linux.c:13: warning: 'struct stat' declared inside parameter list
netslot_linux.c: In function 'find_slot':
netslot_linux.c:24: error: dereferencing pointer to incomplete type
netslot_linux.c: At top level:
netslot_linux.c:68: warning: 'struct FTW' declared inside parameter list
netslot_linux.c:68: warning: 'struct stat' declared inside parameter list
netslot_linux.c: In function 'find_interface':
netslot_linux.c:73: error: dereferencing pointer to incomplete type
netslot_linux.c: In function 'find_interface_slot':
netslot_linux.c:100: error: 'FTW_PHYS' undeclared (first use in this function)
netslot_linux.c:100: error: (Each undeclared identifier is reported only once
netslot_linux.c:100: error: for each function it appears in.)
make[3]: *** [netslot_linux.o] Error 1
make[3]: Leaving directory `/tmp/netperf-2.4.5/src'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/tmp/netperf-2.4.5/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/tmp/netperf-2.4.5'
make: *** [all] Error 2

(In reply to comment #2)
> I downloaded the file from the following address. Switch to the chroot, compile
> netperf-2.4.5 failed. The following error:
> （http://uclibc.org/downloads/binaries/0.9.30.1/system-image-i686.tar.bz2）
> 
> make[3]: Leaving directory `/tmp/netperf-2.4.5/src/missing'
> make[3]: Entering directory `/tmp/netperf-2.4.5/src'
> if gcc -DHAVE_CONFIG_H -I. -I. -I..     -g -O2 -MT netslot_linux.o -MD -MP -MF
> ".deps/netslot_linux.Tpo" \
>           -c -o netslot_linux.o `test -f 'netslot_linux.c' || echo
> './'`netslot_linux.c; \
>         then mv -f ".deps/netslot_linux.Tpo" ".deps/netslot_linux.Po"; \
>         else rm -f ".deps/netslot_linux.Tpo"; exit 1; \
>         fi
> netslot_linux.c:2:17: error: ftw.h: No such file or directory
> netslot_linux.c:13: warning: 'struct FTW' declared inside parameter list
> netslot_linux.c:13: warning: its scope is only this definition or declaration,
> which is probably not what you want
> netslot_linux.c:13: warning: 'struct stat' declared inside parameter list
> netslot_linux.c: In function 'find_slot':
> netslot_linux.c:24: error: dereferencing pointer to incomplete type
> netslot_linux.c: At top level:
> netslot_linux.c:68: warning: 'struct FTW' declared inside parameter list
> netslot_linux.c:68: warning: 'struct stat' declared inside parameter list
> netslot_linux.c: In function 'find_interface':
> netslot_linux.c:73: error: dereferencing pointer to incomplete type
> netslot_linux.c: In function 'find_interface_slot':
> netslot_linux.c:100: error: 'FTW_PHYS' undeclared (first use in this function)
> netslot_linux.c:100: error: (Each undeclared identifier is reported only once
> netslot_linux.c:100: error: for each function it appears in.)
> make[3]: *** [netslot_linux.o] Error 1
> make[3]: Leaving directory `/tmp/netperf-2.4.5/src'
> make[2]: *** [all-recursive] Error 1
> make[2]: Leaving directory `/tmp/netperf-2.4.5/src'
> make[1]: *** [all-recursive] Error 1
> make[1]: Leaving directory `/tmp/netperf-2.4.5'
> make: *** [all] Error 2

What toolchain did you use?
Crosstool-NG?

I downloaded the file from the following address. Switch to the chroot, compile
http://uclibc.org/downloads/binaries/0.9.30.1/system-image-i686.tar.bz2）

# tar xjf system-image-i686.tar.bz2
# tar xjf netperf-2.4.5.tar.bz2 -C rootfs/tmp
# chroot rootfs
# cd /tmp/netperf-2.4.5

/tmp/netperf-2.4.5 # gcc -v
Invoked as gcc
Reference path: /bin/..
arg[ 0] = rawgcc
arg[ 1] = -U__nptl__
arg[ 2] = -v
Using built-in specs.
Target: i686-unknown-linux
Configured with: /home/landley/firmware-0.9.6/build/temp-i686/gcc-core/configure --prefix=/home/landley/firmware-0.9.6/build/mini-native-i686/usr --disable-multilib --build=x86_64-walrus-linux --host=i686-unknown-linux --target=i686-unknown-linux --enable-long-long --enable-c99 --enable-shared --enable-threads=posix --enable-__cxa_atexit --disable-nls --enable-languages=c,c++ --disable-libstdcxx-pch --enable-sjlj-exceptions --program-prefix=
Thread model: posix
gcc version 4.1.2
/tmp/netperf-2.4.5 # ls /lib/libc*
/lib/libc.a                /lib/libcares.so.2         /lib/libcrypt.so.0         /lib/libcurl.so
/lib/libc.so               /lib/libcares.so.2.0.0     /lib/libcrypto.a           /lib/libcurl.so.4
/lib/libc.so.0             /lib/libcom_err.a          /lib/libcrypto.so          /lib/libcurl.so.4.2.0
/lib/libcares.a            /lib/libcrypt-0.9.30.1.so  /lib/libcrypto.so.0.9.8    /lib/libcurses.a
/lib/libcares.la           /lib/libcrypt.a            /lib/libcurl.a             /lib/libcurses.so
/lib/libcares.so           /lib/libcrypt.so           /lib/libcurl.la

/tmp/netperf-2.4.5 # ls /lib/ld-uClibc*
/lib/ld-uClibc-0.9.30.1.so  /lib/ld-uClibc.so.0
/tmp/netperf-2.4.5 # 


CPU： Intel(R) Pentium(R) 4 CPU 2.40GHz
MEM： 512MB

(In reply to comment #4)
> I downloaded the file from the following address. Switch to the chroot, compile
> http://uclibc.org/downloads/binaries/0.9.30.1/system-image-i686.tar.bz2）
> 
> # tar xjf system-image-i686.tar.bz2
> # tar xjf netperf-2.4.5.tar.bz2 -C rootfs/tmp
> # chroot rootfs
> # cd /tmp/netperf-2.4.5
> 
> /tmp/netperf-2.4.5 # gcc -v
> Invoked as gcc
> Reference path: /bin/..
> arg[ 0] = rawgcc
> arg[ 1] = -U__nptl__
> arg[ 2] = -v
> Using built-in specs.
> Target: i686-unknown-linux
> Configured with:
> /home/landley/firmware-0.9.6/build/temp-i686/gcc-core/configure
> --prefix=/home/landley/firmware-0.9.6/build/mini-native-i686/usr
> --disable-multilib --build=x86_64-walrus-linux --host=i686-unknown-linux
> --target=i686-unknown-linux --enable-long-long --enable-c99 --enable-shared
> --enable-threads=posix --enable-__cxa_atexit --disable-nls
> --enable-languages=c,c++ --disable-libstdcxx-pch --enable-sjlj-exceptions
> --program-prefix=
> Thread model: posix
> gcc version 4.1.2
> /tmp/netperf-2.4.5 # ls /lib/libc*
> /lib/libc.a                /lib/libcares.so.2         /lib/libcrypt.so.0       
>  /lib/libcurl.so
> /lib/libc.so               /lib/libcares.so.2.0.0     /lib/libcrypto.a         
>  /lib/libcurl.so.4
> /lib/libc.so.0             /lib/libcom_err.a          /lib/libcrypto.so        
>  /lib/libcurl.so.4.2.0
> /lib/libcares.a            /lib/libcrypt-0.9.30.1.so  /lib/libcrypto.so.0.9.8  
>  /lib/libcurses.a
> /lib/libcares.la           /lib/libcrypt.a            /lib/libcurl.a           
>  /lib/libcurses.so
> /lib/libcares.so           /lib/libcrypt.so           /lib/libcurl.la
> 
> /tmp/netperf-2.4.5 # ls /lib/ld-uClibc*
> /lib/ld-uClibc-0.9.30.1.so  /lib/ld-uClibc.so.0
> /tmp/netperf-2.4.5 # 
> 
> 
> CPU： Intel(R) Pentium(R) 4 CPU 2.40GHz
> MEM： 512MB

Seems like the toolchain's problem.

netperf requires the ftw() function and related structures to be supported by the toolchain. The default configuration of uClibc included in Buildroot makes sure that the generated toolchain has support for ftw():

UCLIBC_HAS_FTW=y

So if you generate a toolchain with Crosstool-NG, it's up to you to make sure that the uClibc of that toolchain has the required features. Buildroot cannot support all possible variants of uClibc configurations, so in a generic way, we only support the configuration we provide in toolchain/uClibc.