[TriLUG] what do crt[1in].o do?

[Joseph Mack NA3T]

I haven't been able to find out much here after a couple of 
days googling.

If you have a single small source file (eg a main() that 
just has "return 0;") you get a small object file. When you 
link to get the executable, about 2k is added. AFAICT, this 
extra code comes from 3 files crt[1in].o. If this is so, I 
should be able to produce the executable directly from the 
.c source code with gcc, or via the .s file using gas/as. I 
can't get the gas/as route to work, which means that I'm not 
using the crt*.o files correctly.

This works

gcc -S main.c		#produces main.s
gcc -o main main.s	#produces executable which runs

This produces an executable that doesn't run

as -o main.o main.s	#
ld -m elf_i386  /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/crtn.o main.o -lc -o main

./main
-bash: ./main: No such file or directory

The missing file seems to be /usr/lib/libc.so.1, (which 
indeed doesn't exist). Linking /usr/lib/libc.so.1 to 
/usr/lib/libc.so gets "permission denied". I don't know why 
-lc picks up /usr/lib/libc.so. If I explicitely use 
/lib/libc.so.6 I get undefined references.

So I have two problems

o I can't produce an executable using the crt*.o files, 
although webpages on the internet use the ld line above 
(sometimes without the -m elf_i386 and sometimes with 
--verbose). I've tried the line above on several machines, 
including ones I haven't setup (and can't have messed up) 
and which are straight installs from a distro on a cd.

o I don't know much about why you can't just make the 
executable from the *.o file without adding 2k of extra 
files. AFAICT some segment (data?) is initialised to 0.
As well the extra code has a start() which is the real start 
of the code. After start() returns, then main() is called. 
When you run the debugger, you don't see any of the code 
before main().

Anyone know what's going on, give me pointer?

Thanks Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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