gcc - Why does arm-linux-gnueabi-g++-4.4 always build a "7-A" binary?

Question

I'm running Ubuntu 12:04LTS and installed arm-linux-gnueabi C and C++ compiler. The compiled binary won't run on my target board. It looks like even if I specify the cpu and arch, the compiler still builds a binary for the wrong CPU. Instead of atm9tdmi it build and 7-A.

Am I doing something wrong or is there something I should have configured? Thanks.

~/ArmTest$ arm-linux-gnueabi-g++-4.4 -mcpu=arm9tdmi -march=armv4t -O main.cpp -o CPPTest

~/ArmTest$ readelf -A CPPTest 
Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "7-A"
  Tag_CPU_arch: v7
  Tag_CPU_arch_profile: Application
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-2
  Tag_FP_arch: VFPv3-D16
  Tag_ABI_PCS_wchar_t: 4
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_align_preserved: 8-byte, except leaf SP
  Tag_ABI_enum_size: int
  Tag_ABI_HardFP_use: SP and DP
  Tag_CPU_unaligned_access: v6
  Tag_DIV_use: Not allowed
~/ArmTest$ file CPPTest 
CPPTest: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.31, BuildID[sha1]=0xf8e81f7a1bb3ee1200cb3dd1aa5b192ecc6de831, not stripped

 uname -a
Linux Desktop 3.2.0-32-generic-pae #51-Ubuntu SMP Wed Sep 26 21:54:23 UTC 2012 i686 athlon i386 GNU/Linux

:~/ArmTest$ arm-linux-gnueabi-g++-4.4 -v
Using built-in specs.
Target: arm-linux-gnueabi
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.7-1ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/arm-linux-gnueabi/include/c++/4.4.7 --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-sjlj-exceptions --with-arch=armv7-a --with-float=softfp --with-fpu=vfpv3-d16 --with-mode=thumb --disable-werror --enable-checking=release --program-prefix=arm-linux-gnueabi- --includedir=/usr/arm-linux-gnueabi/include --build=i686-linux-gnu --host=i686-linux-gnu --target=arm-linux-gnueabi --with-headers=/usr/arm-linux-gnueabi/include --with-libs=/usr/arm-linux-gnueabi/lib
Thread model: posix
gcc version 4.4.7 (Ubuntu/Linaro 4.4.7-1ubuntu2) 

:~/ArmTest$ cat main.cpp
#include<iostream>

using namespace std;

int main(){
   cout<<"Hello World"<<endl;
return 0;
}

Answer 1

Your compiler supports armv4t, problem is your linker has to link your object file with other files like libc, crt.o to create an executable. However in your toolchain all those files have been compiled for 7-A, thus result executable ends up being one as well. This is a problem with ubuntu cross toolchains, they are armv7a by default.

If you just compile your source file, you'll see that compiler outputs right object file type.

$ arm-linux-gnueabi-g++-4.4 -mcpu=arm9tdmi -march=armv4t -O -c main.cpp -o CPPTest

$ readelf -A CPPTest
Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "ARM9TDMI"
  Tag_CPU_arch: v4T
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-1
  Tag_FP_arch: VFPv3-D16
  Tag_ABI_PCS_wchar_t: 4
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_align_preserved: 8-byte, except leaf SP
  Tag_ABI_enum_size: int
  Tag_ABI_HardFP_use: SP and DP
  Tag_ABI_optimization_goals: Prefer Speed
  Tag_DIV_use: Not allowed

So a toolchain is more than a compiler and every component of it needs to play along.