Difference between gcc and ${CC}

Question

Recently I got an NXP imx8 board. And I want to test my programme. But it didn't work on imx8.

When I use aarch64-poky-linux-gcc

$ source /opt/fsl-imx-internal-xwayland/5.15-kirkstone/environment-setup-armv8a-poky-linux
$ aarch64-poky-linux-gcc -o hello hello.c
In file included from hello.c:1:
/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/include/stdio.h:27:10: fatal error: bits/libc-header-start.h: No such file or directory
   27 | #include <bits/libc-header-start.h>
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

when I use ${CC}

$ source /opt/fsl-imx-internal-xwayland/5.15-kirkstone/environment-setup-armv8a-poky-linux

${CC} -o hello hello.c # it can work

So I want to know the reason. And I do this thing:

$ echo 'main(){}'|aarch64-poky-linux-gcc -E -v -
Using built-in specs.
COLLECT_GCC=aarch64-poky-linux-gcc
Target: aarch64-poky-linux
Configured with: ../../../../../../work-shared/gcc-11.2.0-r0/gcc-11.2.0/configure --build=x86_64-linux --host=x86_64-pokysdk-linux --target=aarch64-poky-linux --prefix=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr --exec_prefix=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr --bindir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux --sbindir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux --libexecdir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux --datadir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/share --sysconfdir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/etc --sharedstatedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/com --localstatedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/var --libdir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux --includedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/include --oldincludedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/include --infodir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/share/info --mandir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/share/man --disable-silent-rules --disable-dependency-tracking --with-libtool-sysroot=/home/bamboo/build/5.15-kirkstone-full/fsl-imx-internal-xwayland/mx8m/yocto/build/tmp/work/x86_64-nativesdk-pokysdk-linux/gcc-cross-canadian-aarch64/11.2.0-r0/recipe-sysroot --with-gnu-ld --enable-shared --enable-languages=c,c++ --enable-threads=posix --enable-multilib --enable-default-pie --enable-c99 --enable-long-long --enable-symvers=gnu --enable-libstdcxx-pch --program-prefix=aarch64-poky-linux- --without-local-prefix --disable-install-libiberty --disable-libssp --enable-libitm --enable-lto --disable-bootstrap --with-system-zlib --with-linker-hash-style=gnu --enable-linker-build-id --with-ppl=no --with-cloog=no --enable-checking=release --enable-cheaders=c_global --without-isl --with-gxx-include-dir=/not/exist/usr/include/c++/11.2.0 --with-build-time-tools=/home/bamboo/build/5.15-kirkstone-full/fsl-imx-internal-xwayland/mx8m/yocto/build/tmp/work/x86_64-nativesdk-pokysdk-linux/gcc-cross-canadian-aarch64/11.2.0-r0/recipe-sysroot-native/usr/aarch64-poky-linux/bin --with-sysroot=/not/exist --with-build-sysroot=/home/bamboo/build/5.15-kirkstone-full/fsl-imx-internal-xwayland/mx8m/yocto/build/tmp/work/x86_64-nativesdk-pokysdk-linux/gcc-cross-canadian-aarch64/11.2.0-r0/recipe-sysroot --enable-standard-branch-protection --enable-poison-system-directories --disable-static --enable-nls --with-glibc-version=2.28 --enable-initfini-array --enable-__cxa_atexit
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
COLLECT_GCC_OPTIONS='-E' '-v' '-mlittle-endian' '-mabi=lp64'
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/cc1 -E -quiet -v - -mlittle-endian -mabi=lp64 -dumpbase -
ignoring nonexistent directory "/not/exist/usr/lib/aarch64-poky-linux/11.2.0/include"
ignoring nonexistent directory "/not/exist/usr/local/include"
ignoring nonexistent directory "/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/../../../../../aarch64-poky-linux/include"
ignoring nonexistent directory "/not/exist/usr/include/"
#include "..." search starts here:
#include <...> search starts here:
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/include
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/include-fixed
End of search list.
# 0 "<stdin>"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "<stdin>"
main(){}
COMPILER_PATH=/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/
LIBRARY_PATH=/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/
COLLECT_GCC_OPTIONS='-E' '-v' '-mlittle-endian' '-mabi=lp64'

$ echo 'main(){}'|${CC} -E -v -
Using built-in specs.
COLLECT_GCC=aarch64-poky-linux-gcc
Target: aarch64-poky-linux
Configured with: ../../../../../../work-shared/gcc-11.2.0-r0/gcc-11.2.0/configure --build=x86_64-linux --host=x86_64-pokysdk-linux --target=aarch64-poky-linux --prefix=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr --exec_prefix=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr --bindir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux --sbindir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux --libexecdir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux --datadir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/share --sysconfdir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/etc --sharedstatedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/com --localstatedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/var --libdir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux --includedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/include --oldincludedir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/include --infodir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/share/info --mandir=/usr/local/oe-sdk-hardcoded-buildpath/sysroots/x86_64-pokysdk-linux/usr/share/man --disable-silent-rules --disable-dependency-tracking --with-libtool-sysroot=/home/bamboo/build/5.15-kirkstone-full/fsl-imx-internal-xwayland/mx8m/yocto/build/tmp/work/x86_64-nativesdk-pokysdk-linux/gcc-cross-canadian-aarch64/11.2.0-r0/recipe-sysroot --with-gnu-ld --enable-shared --enable-languages=c,c++ --enable-threads=posix --enable-multilib --enable-default-pie --enable-c99 --enable-long-long --enable-symvers=gnu --enable-libstdcxx-pch --program-prefix=aarch64-poky-linux- --without-local-prefix --disable-install-libiberty --disable-libssp --enable-libitm --enable-lto --disable-bootstrap --with-system-zlib --with-linker-hash-style=gnu --enable-linker-build-id --with-ppl=no --with-cloog=no --enable-checking=release --enable-cheaders=c_global --without-isl --with-gxx-include-dir=/not/exist/usr/include/c++/11.2.0 --with-build-time-tools=/home/bamboo/build/5.15-kirkstone-full/fsl-imx-internal-xwayland/mx8m/yocto/build/tmp/work/x86_64-nativesdk-pokysdk-linux/gcc-cross-canadian-aarch64/11.2.0-r0/recipe-sysroot-native/usr/aarch64-poky-linux/bin --with-sysroot=/not/exist --with-build-sysroot=/home/bamboo/build/5.15-kirkstone-full/fsl-imx-internal-xwayland/mx8m/yocto/build/tmp/work/x86_64-nativesdk-pokysdk-linux/gcc-cross-canadian-aarch64/11.2.0-r0/recipe-sysroot --enable-standard-branch-protection --enable-poison-system-directories --disable-static --enable-nls --with-glibc-version=2.28 --enable-initfini-array --enable-__cxa_atexit
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
COLLECT_GCC_OPTIONS='-march=armv8-a+crc+crypto' '-fstack-protector-strong' '-O2' '-D' '_FORTIFY_SOURCE=2' '-Wformat=1' '-Wformat-security' '-Werror=format-security' '-E' '-v' '-mlittle-endian' '-mabi=lp64'
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/cc1 -E -quiet -v -isysroot /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux -D _FORTIFY_SOURCE=2 - -march=armv8-a+crc+crypto -mlittle-endian -mabi=lp64 -Wformat=1 -Wformat-security -Werror=format-security -fstack-protector-strong -O2 -dumpbase -
ignoring nonexistent directory "/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/usr/local/include"
ignoring nonexistent directory "/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/../../../../../aarch64-poky-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/include
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/usr/lib/aarch64-poky-linux/11.2.0/include
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/include-fixed
 /opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/usr/include/
End of search list.
# 0 "<stdin>"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "<stdin>"
main(){}
COMPILER_PATH=/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/
LIBRARY_PATH=/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/x86_64-pokysdk-linux/usr/lib/aarch64-poky-linux/gcc/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/lib/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/usr/lib/aarch64-poky-linux/11.2.0/:/opt/fsl-imx-internal-xwayland/5.15-kirkstone/sysroots/armv8a-poky-linux/usr/lib/
COLLECT_GCC_OPTIONS='-march=armv8-a+crc+crypto' '-fstack-protector-strong' '-O2' '-D' '_FORTIFY_SOURCE=2' '-Wformat=1' '-Wformat-security' '-Werror=format-security' '-E' '-v' '-mlittle-endian' '-mabi=lp64'

I found that they both use aarch64-poky-linux-gcc. But I still don't know the difference between them.

Answer 1

gcc is the name of a command. Your shell will look for it in the path .

${CC} is a variable substitution. Your shell will look for it in the environment of the shell process.

Answer 2

gcc is the compiler of your machine. You can find which one and where is located like this:

• readlink -f $(which gcc) : this will show you the path of the program used
• gcc --version : will show you the version of your gcc compiler

In case you are building in a PC, then the gcc will build programs for x86 architectures. In your case you need a compiler to generate programs for arm64 architectures (the opensource is aarch64-linux-gnu-gcc but the providers usually give you a modified toolchain with the compiler and all necessary libraries/headers.

When you crosscompile, you must " source " an environment file, this will modify the environment variables in the terminal were you sourced the environment file this will create the environment variable CC , this will contains the path to the compiler with some parameters for the compiler.

If you run echo ${CC} you will see the toolchain and the parameters.

The idea always is to have an isolated environment which doesn't depend on the OS, gcc version of the host PC, that's why you were provided with the compiler and you must use ${CC} to crosscompile to the architecture arm which is the base of imx SOCs