Question

I am trying to link a static third party library compiled with RVCT 2.2 with a test program compiled with GCC (arm-none-linux-gnueabi-gcc Sourcery G++ Lite 2011.03-41).

If I link with -static, everything works as it should. If I do not use -static however, I get lots of complaints like the following:

foolib.a(foo.o): In function `foofunc':
foo.c:(.text+0x4c8): undefined reference to `__aeabi_memcpy'
foolib.a(bar.o): In function `barfunc':
bar.c:(.text+0xa54): undefined reference to `__aeabi_memclr4'

Both memcpy and memset should be present in libc.
Clearly GCC can somehow detect and fix this if I use -static. Can someone explain what is happening? I assume that GCC dynamically links to libc unless I add the -static flag, but shouldn’t __aeabi_memcpy and similar be defined in the shared libc library as well?

EDIT:
In order to let people test this themselves I have now created a minimalistic test case like follows:

//foo.c
#include <string.h>

void foo(void *dst, void *src, int num) {
    memcpy(dst, src, num);
}

This file is compiled and archived with RVCT 2.2 as follows:

armcc.exe --arm -c --apcs=/noswst/interwork foo.c -o foo.o
armar.exe --create foo.a foo.o

This library is then linked with the following test program:

//bar.c
#include <stdio.h>
extern void foo(void *dst, void *src, int num);
int main(int argc, char *argv[]) {
    int a[10], b[10], i;

    for (i = 0; i < 10; i++) {
            a[i] = i;
    }

    foo(b, a, sizeof(a));

    for (i = 0; i < 10; i++) {
            if (a[i] != b[i]) {
                    printf("Diff at %d: %d != %d\n", i, a[i], b[i]);
                    return 1;
            }
    }
    printf("Success!\n");
    return 0;
}

Using the following command:

arm-none-linux-gnueabi-gcc -Wall bar.c foo.a -o bar

Which gives the following output (unless -static is also used):

foo.a(foo.o): In function `foo':
foo.c:(.text+0x0): undefined reference to `__aeabi_memcpy'
arm-none-linux-gnueabi/bin/ld: bar: hidden symbol `__aeabi_memcpy' isn't defined
arm-none-linux-gnueabi/bin/ld: final link failed: Nonrepresentable section on output
collect2: ld returned 1 exit status

The binary foo.a can be downloaded from http://dl.dropbox.com/u/14498565/foo.a in case you don’t have RVCT.

Answer 1

After spending some time with this @Leo, I think I understand what’s going on. It appears that foo.o was compiled in a way that expects a static link to __aeabi_memcpy. Looking at foo.o with arm-none-linux-gnueabi-objdump -t, I see this:

foo.o:     file format elf32-littlearm

SYMBOL TABLE:
00000000 l    df *ABS*  00000000 foo.c
00000000 l    d  .text  00000000 .text
00000000 l       *ABS*  00000000 BuildAttributes$$THUMB_ISAv1$ARM_ISAv4$M$PE$A:L22$X:L11$S22$IEEE1$IW$USESV6$~STKCKD$USESV7$~SHL$OSPACE$EBA8$REQ8$PRES8$EABIv2
00000000 l     O .debug_frame$$$.text   00000000 C$debug_frame$$$.text7
00000000  w    F *UND*  00000000 .hidden Lib$$Request$$armlib
00000000       F *UND*  00000000 .hidden __aeabi_memcpy
00000000 g     F .text  00000004 .hidden foo

Note the -t in the command line… that’s for showing us the static symbols (non-shared). Running arm-none-linux-gnueabi-objdump -T on foo.o shows this:

foo.o:     file format elf32-littlearm

/home/jszakmeister/.local/sourcery-arm-gnueabi/bin/arm-none-linux-gnueabi-objdump: foo.o: not a dynamic object
DYNAMIC SYMBOL TABLE:
no symbols

So __aeabi_memcpy is looking to be resolved via a static link, which is why using -static works. I believe if you compiled foo.o a little differently, so that it expects a shared C library, then you could link to foo.a without specifying -static. Unfortunately, I’m not familiar with the RVCT compiler, or I’d tell you how.

FWIW, using strace I was able to see that it is indeed linking against the shared C library, but not resolving the link. I also used the --sysroot=/path/to/code/sourcery/toolchain/arm-none-linux-gnueabi/libc command line option to make sure it was finding the correct C library.