Linking with another start-up file

Question

I am trying to link a program with my own start-up file by using the STARTUP directive in a LD script:

...
ENTRY(_start)
STARTUP(my_crt1.o)
...

GCC driver is used to link the program (not to bother with library paths like libgcc, etc.):

gcc -T my_script.ld ...

Unfortunately, it only works with a GCC compiled for powerpc targets, while arm or i686 targets don't and still include crt0.o in collect2. For example:

arm-eabi-g++ -v -T my_script.ld ...

gives me:

collect2 ... /opt/lib/gcc/arm-eabi/4.8.0/../../../../arm-eabi/lib/crt0.o ...

and thus:

crt0.S:101: multiple definition of `_start'

It seems the STARTUP directive is totally ignored (the powerpc target uses its default crt0 too unless the STARTUP directive is specified) and there is no way to disable the default crt0.

Is there a portable way to link against another start-up file?

My start-up file uses libgcc functions (to call ctors and dtors) so crtbegin.o, crtend.o, etc. are needed so I would like to avoid the -nostartfiles option which disables crt*.o - I need to disable crt0.o only.

Thank you

Answer 1

I am trying to link a program with my own start-up file ...
GCC driver is used to link the program ...

In that case, you must also supply -nostartfiles flag to GCC.

Answer 2

This limitation indeed forces you to disable the default startup files with -nostartfiles (I prefer -nostdlib). You then need to build by yourself the list of run-time objects. gcc has the option -print-file-name to print the absolute path of libraries it was compiled with (crtbegin.o, crtend.o, libgcc.a...). For example: arm-eabi-g++ <FLAGS> -print-file-name=crtbegin.o

Here is the GNU Make macro I use (providing gcc and cflags):

define m.in/toolchain/gnu/locate =
$(strip
  $(shell $(m.in/toolchain/gnu/bin/gcc) $(m.in/toolchain/gnu/cflags) \
          -print-file-name=$(m.in/argv/1))
)
endef

crtn := $(call m.in/toolchain/gnu/locate, crtn.o)