Re: ld(1) cannot find entry symbol _start;
> From owner-freebsd-questi...@freebsd.org Wed Sep 29 05:50:13 2010
> Date: Wed, 29 Sep 2010 11:51:09 +0100 (BST)
> From: Anton Shterenlikht
> To: Michel Talon
> Cc: freebsd-questions@freebsd.org
> Subject: Re: ld(1) cannot find entry symbol _start;
>
>
>
> On Tue, 28 Sep 2010, Michel Talon wrote:
>
> > Paul B Mahol said:
> > On 9/28/10, Anton Shterenlikht 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
> > D __progname
> > U _fini
> > U _init
> > U _init_tls
> > T _start
> > 0020 t _start1
> > r abitag
> > U atexit
> > 0004 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.
Those routines set up the "run-time envrionment" that any UNIX
c-language evironment expects. that's that the name 'crt' prefix
means '-language un-ime' this involves a bunch of 'gory
mechanical details' that *DON'T* really matter how they get
accomplished, jus that they _do_ get done. This includes things
like setting up the 'stack', and the 'heap', initializing the tables
for the dynamic-memory management routines (malloc and friends),
setting up 'stdin/stdout/stderr', and getting the command-line arguments
processed so that they can be passed as 'argc', and 'argv' (also the
'environment', in 'envp') to your 'main()' program.
>
> 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
> which aren't?
"who cares?" applies. it is all simmply "required housekeeping"
go bring the state of the current running process (i.e, the task/
address-space/etc) to what is defined as the 'initial state' for
a c-language 'main()' program.
>
> For example if I use g95 compiler instead of gfortran45,
> will the linker still need all above object files?
If you use 'the compiler' to manage the linking process -- e.g.
{compilername} -o {executable} {one-or-more-'object' .o file}
the right files will be automatically included in the executable.
'crt0.o' is the classical program entry point -- it may or may not
rely on other routines to get 'the environment' set up -- especially
depending on what 'advanced' features the program uses.. If you use
light-weight-process 'threads' (-lpthread) this may call for different
crt0 code.
Unless you are engaged in porting the compiler and O/S to a completely
new hardware architecture, or trying to generate 'stand-alone' code, e.g.
for an embedded processor tht runs witout _anuting called a 'cpu', you
don't have any reason to worry about this housekeeping code. Its there,
it works, and it does what it's supposed to.Oh yeah, if you
tamper with it, you make it incompatible with the use of _any_ existing
object files.
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Re: ld(1) cannot find entry symbol _start;
On Tue, 28 Sep 2010, Michel Talon wrote: Paul B Mahol said: On 9/28/10, Anton Shterenlikht 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 D __progname U _fini U _init U _init_tls T _start 0020 t _start1 r abitag U atexit 0004 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 which aren't? For example if I use g95 compiler instead of gfortran45, will the linker still need all above object files? many thanks anton ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
Re: ld(1) cannot find entry symbol _start;
Paul B Mahol said: On 9/28/10, Anton Shterenlikht 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 D __progname U _fini U _init U _init_tls T _start 0020 t _start1 r abitag U atexit 0004 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 ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
Re: ld(1) cannot find entry symbol _start;
On 9/28/10, Anton Shterenlikht wrote:
> I'm trying to learn the very basics of the
> compile - assemble - link process on FreeBSD.
> Please don't shoot me.
>
> I've this c code:
>
> % cat tmp.c
> int main() {
> int a;
> int b;
> int c;
>
> a = 2;
> b = 3;
>
> c=a*b;
> }
>
> which I compile into assembly language:
>
> % gcc -v
> Using built-in specs.
> Target: ia64-undermydesk-freebsd
> Configured with: FreeBSD/ia64 system compiler
> Thread model: posix
> gcc version 4.2.1 20070719 [FreeBSD]
>
> % gcc -S tmp.c
>
> I then assemble the object file:
>
> % gcc -o tmp.o -c tmp.s
> % file tmp.o
> tmp.o: ELF 64-bit LSB relocatable, IA-64, version 1 (FreeBSD), not stripped
>
> Then I try to link the object file into
> an executable:
>
> % ld tmp.o
You are missing something in above command.
> ld: warning: cannot find entry symbol _start; defaulting to 20f0
>
> Finally, when I try to run the executable,
> I get segfault:
>
> % ./a.out
> Segmentation fault (core dumped)
>
>
> Looking at the asm listing, there is indeed no
> _start symbol:
>
>
> .file "tmp.c"
> .pred.safe_across_calls p1-p5,p16-p63
> .text
> .align 16
> .global main#
> .proc main#
> main:
> .prologue 2, 2
> .vframe r2
> mov r2 = r12
> .body
> ;;
> adds r15 = 8, r2
> addl r14 = 2, r0
> ;;
> st4 [r15] = r14
> adds r15 = 4, r2
> addl r14 = 3, r0
> ;;
> st4 [r15] = r14
> adds r14 = 8, r2
> adds r15 = 4, r2
> ;;
> ld4 r16 = [r14]
> ld4 r14 = [r15]
> ;;
> setf.sig f6 = r16
> setf.sig f7 = r14
> ;;
> xmpy.l f6 = f6, f7
> ;;
> getf.sig r14 = f6
> ;;
> st4 [r2] = r14
> .restore sp
> mov r12 = r2
> br.ret.sptk.many b0
> ;;
> .endp main#
> .ident "GCC: (GNU) 4.2.1 20070719 [FreeBSD]"
>
>
> What am I missing?
>
> I'm happy to be referred to FM.
>
> many thanks
> anton
>
> --
> Anton Shterenlikht
> Room 2.6, Queen's Building
> Mech Eng Dept
> Bristol University
> University Walk, Bristol BS8 1TR, UK
> Tel: +44 (0)117 331 5944
> Fax: +44 (0)117 929 4423
> ___
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ld(1) cannot find entry symbol _start;
I'm trying to learn the very basics of the
compile - assemble - link process on FreeBSD.
Please don't shoot me.
I've this c code:
% cat tmp.c
int main() {
int a;
int b;
int c;
a = 2;
b = 3;
c=a*b;
}
which I compile into assembly language:
% gcc -v
Using built-in specs.
Target: ia64-undermydesk-freebsd
Configured with: FreeBSD/ia64 system compiler
Thread model: posix
gcc version 4.2.1 20070719 [FreeBSD]
% gcc -S tmp.c
I then assemble the object file:
% gcc -o tmp.o -c tmp.s
% file tmp.o
tmp.o: ELF 64-bit LSB relocatable, IA-64, version 1 (FreeBSD), not stripped
Then I try to link the object file into
an executable:
% ld tmp.o
ld: warning: cannot find entry symbol _start; defaulting to 20f0
Finally, when I try to run the executable,
I get segfault:
% ./a.out
Segmentation fault (core dumped)
Looking at the asm listing, there is indeed no
_start symbol:
.file "tmp.c"
.pred.safe_across_calls p1-p5,p16-p63
.text
.align 16
.global main#
.proc main#
main:
.prologue 2, 2
.vframe r2
mov r2 = r12
.body
;;
adds r15 = 8, r2
addl r14 = 2, r0
;;
st4 [r15] = r14
adds r15 = 4, r2
addl r14 = 3, r0
;;
st4 [r15] = r14
adds r14 = 8, r2
adds r15 = 4, r2
;;
ld4 r16 = [r14]
ld4 r14 = [r15]
;;
setf.sig f6 = r16
setf.sig f7 = r14
;;
xmpy.l f6 = f6, f7
;;
getf.sig r14 = f6
;;
st4 [r2] = r14
.restore sp
mov r12 = r2
br.ret.sptk.many b0
;;
.endp main#
.ident "GCC: (GNU) 4.2.1 20070719 [FreeBSD]"
What am I missing?
I'm happy to be referred to FM.
many thanks
anton
--
Anton Shterenlikht
Room 2.6, Queen's Building
Mech Eng Dept
Bristol University
University Walk, Bristol BS8 1TR, UK
Tel: +44 (0)117 331 5944
Fax: +44 (0)117 929 4423
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