ld(1) cannot find entry symbol _start;
mexas at bristol.ac.uk
Wed Sep 29 10:51:11 UTC 2010
On Tue, 28 Sep 2010, Michel Talon wrote:
> Paul B Mahol said:
> On 9/28/10, Anton Shterenlikht <mexas at 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
> where the object file produced by compilation and assembling is
> 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
> 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.
thank you. Where can I read more on what each file is for:
% ls -al /usr/lib/crt*
-r--r--r-- 1 root wheel 2552 Sep 15 13:52 /usr/lib/crt1.o
-r--r--r-- 1 root wheel 4656 Sep 15 13:53 /usr/lib/crtbegin.o
-r--r--r-- 1 root wheel 4936 Sep 15 13:53 /usr/lib/crtbeginS.o
-r--r--r-- 1 root wheel 4656 Sep 15 13:53 /usr/lib/crtbeginT.o
-r--r--r-- 1 root wheel 3648 Sep 15 13:53 /usr/lib/crtend.o
-r--r--r-- 1 root wheel 3648 Sep 15 13:53 /usr/lib/crtendS.o
-r--r--r-- 1 root wheel 1928 Sep 15 13:52 /usr/lib/crti.o
-r--r--r-- 1 root wheel 1087 Sep 15 13:52 /usr/lib/crtn.o
The sources for these files are in asm, so would be good
to read a more accessible introduction.
Also, it seems only crt1, crti and crtn are provided
by FreeBSD itself (/usr/src/lib/csu/ia64), crtbegin and
crtend are under /usr/src/contrib/gcc/config/ia64/,
and sources for *S.o and *T.o I can't find at all.
So which of these are specific to GCC on FreeBSD, and
For example if I use g95 compiler instead of gfortran45,
will the linker still need all above object files?
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