Date: Tue, 28 Sep 2010 13:54:14 +0000 From: Michel Talon <talon@lpthe.jussieu.fr> To: freebsd-questions@freebsd.org Subject: Re: ld(1) cannot find entry symbol _start; Message-ID: <20100928135414.GA17159@lpthe.jussieu.fr>
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Paul B Mahol said:
On 9/28/10, Anton Shterenlikht <mexas@bristol.ac.uk> wrote:
> > I'm trying to learn the very basics of the
> > compile - assemble - link process on FreeBSD.
> > Please don't shoot me.
> ....
> > Then I try to link the object file into
> > an executable:
> >
> > % ld tmp.o
>
> You are missing something in above command.
>
More precisely, if you run gcc -v on a C file you get someting like:
/usr/bin/ld --eh-frame-hdr -V -dynamic-linker /libexec/ld-elf.so.1
/usr/lib/crt1.o /usr/lib/crti.o /usr/lib/crtbegin.o -L/usr/lib
-L/usr/lib /var/tmp//cco5EINk.o -lgcc --as-needed -lgcc_s --no-as-needed
-lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/crtend.o
/usr/lib/crtn.o
where the object file produced by compilation and assembling is
/var/tmp//cco5EINk.o
That is adds several other object files to your own in order to get
an executable.
In particular the start symbol, at which execution begins is in
/usr/lib/crt1.o
as you can see from
niobe% nm /usr/lib/crt1.o
w _DYNAMIC
00000000 D __progname
U _fini
U _init
U _init_tls
00000000 T _start
00000020 t _start1
00000000 r abitag
U atexit
00000004 C environ
U exit
U main
which shows that _start is defined here, (but not e.g. _init). On the
other hand the function main() which is defined in your program is
referred to but undefined here.
--
Michel TALON
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