Symbols in dylib, Works with gcc-4.0 not in gcc-4.2 (OSX-default)

Question

hi,

i'v got an dynamic-Lib which i build with

OBJECTS=keys.o etc2.o foo.o
$(CC) -DSYS_MACOSX  -g -fPIC -flat_namespace -L. -lpthread  -Wl,-flat_namespace -dynamiclib  -shared -o libmylib.dylib $(OBJECTS)

My test progam links with this library

$(CC) -DSYS_MACOSX  -g -fPIC testmain.c -o testmain -I. -flat_namespace -L. -lpthread  -lmylib 

When CC=gcc-4.2 I get following error in gdb, when I try to access const symbols in libmylib.dylib:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000112dd0
0x0000000100004ec7 in extractKeyFromList (keyList=0x112dd0, key=0x1002001e0 "Adresse1.aName1") at keys.c:148

The programm works, with:

• gcc-4.0 on SnowLeopard
• gcc-4.3.2 on Debian i386
• gcc-4.1.2 for arm-angstrom-linux-gnueabi

Update: Here is some debug-output main=main loadKeyList=function in Lib

GCC 4.0:

main:            sizeof KeyList =  149480
loadKeyList:     sizeof KeyList =  149480
loadKeyList:     list at 0xfe88c
loadKeyList:     sizeof list =  149480
loadKeyList:     list->count 3086
main:            sizeof handle->keyList = 149480
main:            handle->keyList at 0xfe88c
main:            handle->keyList->count 3086

GCC4.2

(gdb) run
Starting program: keyextractor -k Adresse1.aName1
Reading symbols for shared libraries ++. done
main:            sizeof KeyList =  166088
loadKeyList:     sizeof KeyList =  166088
loadKeyList:     list at 0x112dd0
loadKeyList:     sizeof list =  166088
loadKeyList:     list->count 3086
main:            sizeof handle->keyList = 166088
main:            handle->keyList at 0x112dd0

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000112dd0
0x0000000100001940 in main (argc=3, argv=0x7fff5fbfefb8) at keyextractor.c:110
110     printf("main:            handle->keyList->count %i\n", handle->keyList->count);
(gdb) 

The Struct looks like this:

typedef struct _KeyList {
    int count;
    Key keys[4152];
} KeyList;

Update 2: This works in gcc-4.2 from main

printf("KEYMAP.keyList[5] at 0x%x count = %i\n", &KEYMAP.keyList[5], KEYMAP.keyList[5].count);
Output: KEYMAP.keyList[5] at 0x112dd0 count = 3086

That's the same adress like pointer handle->keyList!

KEYMAP looks like:

typedef struct _KeyMapList {
    int count;
    KeyList keyList[];
} KeyMapList;

const KeyMapList KEYMAP = {
  .count = 6,
  .keyList = {
   { ... }, { .... },
   { ... }, { .... },
   { ... }, { .count=3086, keys.... }
   }
};

So whats the problem with gcc-4.2?

Thanks

Answer 1

ok .. it seems not to be a problem with gcc.

It's a problem with the x86_64-Architecture. Building with "-arch i386" solves the problem with gcc4.2.

I still don't know, why it doesn't work with x86_64. Both binary and dylib are x86_64:

libmylib.dylib: Mach-O 64-bit dynamically linked shared library x86_64
keyextractor:   Mach-O 64-bit executable x86_64

Answer 2

My program failed on Linux-x86_64, too

But the real answer is: you should listen to gcc warnings and compile with -Wall

 keyextractor.c:114: warning: cast to pointer from integer of different size

This warning was in the line, where I called a function from the Lib, without #include-ing the respective Header-File. Without function-declartion it worked:

• i386-architecture as shared lib and static
• x86_64-architecture only static

So, after including the right header-file, everything worked fine.