Undefined reference to strlen, although library is supplied

[Hermann-Simon Lichte]

Hello everybody,

first, I'd like to thank everyone who responded to my first mail 
concerning the powerpc-eabi compiler build. Especially, I found Kai's 
hints the most productive ones, and by taking his steps into 
consideration, the build was just a piece of cake.

I am now trying to build a simple C++ application with my powerpc-eabi 
compiler. I have written an appropriate linker configuration file that 
fits my target development board (a Phytec phyCORE-MPC555 hooked up 
using the Wiggler interface, just in case one likes to know).

The final link fails due to an undefined reference to strlen. However, 
this function is present in libc.a, and even though I tell the linker to 
use libc.a, it keeps complaining. An objdump reveals its presence, the 
linker flags seem fine to me, so how come it doesn't link properly?

I tried to build my application earlier with success by using a 
pre-defined architecture (such as ads, yellowknife etc.) Then, the 
linking stage finishes properly. Now, I want to leave out the -mads 
option. I created a system.o file that contains the required system 
functions (_exit, sbrk, getpid, and kill) with a minimal implementation 
similar to those suggested in the Newlib documentation.

To make things a little clearer, here are the error messages and some dumps:

$ make all
powerpc-eabi-gcc -mcpu=505 -c src/system.c -o src/system.o
powerpc-eabi-gcc -mcpu=505 -c src/main.cc -o src/main.o
powerpc-eabi-gcc -mcpu=505 -c src/LED.cc -o src/LED.o
powerpc-eabi-gcc -T phycore555.ld -o build/blinky++.elf src/system.o 
src/LED.o src/main.o -lstdc++ -lg -lc
/usr/local/lib/gcc-lib/powerpc-eabi/3.3.2/../../../../powerpc-eabi/bin/ld: 
warning: cannot find entry symbol _start; defaulting to 00802000
/usr/local/lib/gcc-lib/powerpc-eabi/3.3.2/libgcc.a(unwind-dw2.o)(.text+0x3e4): 
In function `extract_cie_info':
/home/gem/crossgcc/gcc-3.3.2/gcc/unwind-dw2.c:247: undefined reference 
to `strlen'
/usr/local/lib/gcc-lib/powerpc-eabi/3.3.2/libgcc.a(unwind-dw2.o)(.text+0xd08): 
In function `execute_cfa_program':
/home/gem/crossgcc/gcc-3.3.2/gcc/unwind-dw2.c:820: undefined reference 
to `memcpy'
----(Snip)----------------------------------------------------------------------

powerpc-eabi-nm tells me that strlen as well as memcpy are defined.
An objdump of libc.a also shows me their presences.

$ powerpc-eabi-objdump -d -X `powerpc-eabi-gcc -print-file-name=libc.a`

----(Snip)----------------------------------------------------------------------
strlen.o:     file format elf32-powerpc
rw-r--r-- 16162/22680   7244 Feb  6 10:26 2004 strlen.o
architecture: powerpc:common, flags 0x00000011:
HAS_RELOC, HAS_SYMS
start address 0x00000000

....

Disassembly of section .text:

00000000 <strlen>:
    0:   70 60 00 03     andi.   r0,r3,3
    4:   94 21 ff e0     stwu    r1,-32(r1)
    8:   7c 6a 1b 78     mr      r10,r3
    c:   40 82 00 44     bne-    50 <strlen+0x50>
----(Snip)----------------------------------------------------------------------

I don't understand why the linker doesn't resolve the references. Maybe 
I am still not supplying the right flags to it, but maybe it's a totally 
different problem that I am not yet aware about. What also bothers me is 
that by supplying -mads (or -myellowknife) to the linker (without my 
system.o) the linking stage succeeds. It seems likely to me that there 
are still things left to consider.

If I am not totally mislead, I believe that, in addition, I still need 
to write startup code for my target. By leaving out -mads it is not 
using any crt0, is it? What does actually need to be done in crt0? Is it 
sufficient to just set up the initial stack frame? To make global 
variables work, specific processor registers also need to be set up, as 
far as I know (I think they are R2, table of contents, and R13, global 
data, but I will do more research on that). What else needs to be 
included in a typical crt0 for an embedded target such as mine?

----(Snip)----------------------------------------------------------------------
/usr/local/lib/gcc-lib/powerpc-eabi/3.3.2/libgcc.a(eabi.o)(.text+0xc4): 
In function `__eabi':
/home/gem/crossgcc/build-gcc/gcc/eabi.S:232: undefined reference to `__init'
----(Snip)----------------------------------------------------------------------

Anyway, IMHO, a missing crt0 does not explain the unresolved strlen and 
memcpy references. There must be another reason for that.

I am about to dig a littler deeper into the predefined libglosses 
(reading sources). I am still new to embedded development, and this is a 
very nice adventure trip for me.

So this is why I am asking kindly for another push into the right 
direction. Such a discussion on the mailing list might also be helpful 
for others digging into this subject as well.

Thank you all.

Hermann



------
Want more information?  See the CrossGCC FAQ, http://www.objsw.com/CrossGCC/
Want to unsubscribe? Send a note to crossgcc-unsubscribe@sources.redhat.com