Examining gcc behavior

Posted by Vivek Gite [Last updated: June 22, 2006]

Recently my friend highlighted something that can be use to examining gcc complier behavior.

You can pass following options to gcc

-v : Display the commands executed to run the stages of compilation on screen.
-x language : I am using C
/dev/null : Use /dev/null as input file

For example when I type the following command:

gcc -v -x c /dev/null

Output:

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --program-suffix=-4.0 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-java-awt=gtk-default --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr --disable-werror --with-tune=i686 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.0.4 20060507 (prerelease) (Debian 4.0.3-3)
 /usr/lib/gcc/i486-linux-gnu/4.0.4/cc1 -quiet -v /dev/null -quiet -dumpbase null -mtune=i686 -auxbase null -version -o /tmp/ccMVab5b.s
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i486-linux-gnu/4.0.4/include
 /usr/include
End of search list.
GNU C version 4.0.4 20060507 (prerelease) (Debian 4.0.3-3) (i486-linux-gnu)
        compiled by GNU C version 4.0.4 20060507 (prerelease) (Debian 4.0.3-3).
GGC heuristics: --param ggc-min-expand=81 --param ggc-min-heapsize=96075
 as -V -Qy --32 -o /tmp/ccyCAfmi.o /tmp/ccMVab5b.s
GNU assembler version 2.16.91 (i486-linux-gnu) using BFD version 2.16.91 20060413 Debian GNU/Linux
 /usr/lib/gcc/i486-linux-gnu/4.0.4/collect2 --eh-frame-hdr -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/gcc/i486-linux-gnu/4.0.4/../../../../lib/crt1.o /usr/lib/gcc/i486-linux-gnu/4.0.4/../../../../lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.0.4/crtbegin.o -L/usr/lib/gcc/i486-linux-gnu/4.0.4 -L/usr/lib/gcc/i486-linux-gnu/4.0.4 -L/usr/lib/gcc/i486-linux-gnu/4.0.4/../../../../lib -L/usr/lib/gcc/i486-linux-gnu/4.0.4/../../.. -L/lib/../lib -L/usr/lib/../lib /tmp/ccyCAfmi.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i486-linux-gnu/4.0.4/crtend.o /usr/lib/gcc/i486-linux-gnu/4.0.4/../../../../lib/crtn.o
/usr/lib/gcc/i486-linux-gnu/4.0.4/../../../../lib/crt1.o: In function `_start':
../sysdeps/i386/elf/start.S:115: undefined reference to `main'
collect2: ld returned 1 exit status

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