Minimal program crashes, depending on linker script

[Carsten Fuchs]

Dear group,

attached please find a very small program that reproducibly crashes on a 
Debian Sarge and two distinct kubuntu 5.10 systems.

The crash does *not* occur when the line with the comment in the 
Makefile is modified, so that either the "linker-script" *or* the 
"-Wl,-Bsymbolic" statement is added to the link command line.


The problem is that I don't understand why this is so, but would love to 
learn the background and understand the reason for the crash, when 
neither the linker script nor the -Bsymbolic flag enters the link 
command line.

(I've bought and currently read the "Loaders and Linkers" book by John 
R. Levine, but my assembly skills are limited and so I make positive but 
slow progress.)

Below I'm including a session log trying to debug the crash. I've 
inserted newlines for clarity, and must add that I'm not able to 
interprete all of the output.

I'd be very grateful for any advice about this problem or any help to 
understand what causes it!

Thank you very much, and best regards,
Carsten



carsten@ThuBi-Blue:/mnt/WinD/System/Linux/TestCrash2$ make
g++ -Wall -g -c test.cpp -o test.o
g++ test.o -lGL -o test
g++ -fPIC -Wall -g -c dso.cpp -o dso.o
g++ -shared dso.o -o dso.so # linker-script   # -Wl,-Bsymbolic

carsten@ThuBi-Blue:/mnt/WinD/System/Linux/TestCrash2$ ./test
1: Beginning...
2: glActiveStencilFaceEXT = 0x4009b69c
Ungültiger Maschinenbefehl

carsten@ThuBi-Blue:/mnt/WinD/System/Linux/TestCrash2$ gdb ./test
GNU gdb 6.3-debian
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain 
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-linux"...Using host libthread_db 
library "/lib/tls/libthread_db.so.1".

(gdb) run
Starting program: /mnt/WinD/System/Linux/TestCrash2/test
1: Beginning...
2: glActiveStencilFaceEXT = 0x4009b69c

Program received signal SIGILL, Illegal instruction.
0x4009b6a0 in glActiveStencilFaceEXT () from /usr/X11R6/lib/libGL.so.1

(gdb) list
1       #include <stdio.h>
2       #include <dlfcn.h>
3
4
5       extern "C" { typedef void (*GetRendererT)(); }
6
7
8       int main(int ArgC, const char* ArgV[])
9       {
10          void* RendererDLL=dlopen("./dso.so", RTLD_NOW);

(gdb) where
#0  0x4009b6a0 in glActiveStencilFaceEXT () from /usr/X11R6/lib/libGL.so.1
#1  0x00200206 in ?? ()
#2  0x40b7e8e1 in GetRenderer () at dso.cpp:14
#3  0x08048700 in main (ArgC=1, ArgV=0xbffff854) at test.cpp:16

(gdb) bt full
#0  0x4009b6a0 in glActiveStencilFaceEXT () from /usr/X11R6/lib/libGL.so.1
No symbol table info available.
#1  0x00200206 in ?? ()
No symbol table info available.
#2  0x40b7e8e1 in GetRenderer () at dso.cpp:14
No locals.
#3  0x08048700 in main (ArgC=1, ArgV=0xbffff854) at test.cpp:16
        RendererDLL = (void *) 0x804a360
        GetRenderer = 0x40b7e874 <GetRenderer>

(gdb) x/4i $pc
0x4009b6a0 <glActiveStencilFaceEXT+4>:  (bad)
0x4009b6a1 <glActiveStencilFaceEXT+5>:  (bad)
0x4009b6a2 <glActiveStencilFaceEXT+6>:  jmp    *0xaf0(%eax)
0x4009b6a8 <glActiveStencilFaceEXT+12>: int3

(gdb) x/10i $pc-15
0x4009b691 <glVertexAttribs4hvNV+21>:   int3
0x4009b692 <glVertexAttribs4hvNV+22>:   int3
0x4009b693 <glVertexAttribs4hvNV+23>:   int3
0x4009b694 <glVertexAttribs4hvNV+24>:   int3
0x4009b695 <glVertexAttribs4hvNV+25>:   int3
0x4009b696 <glVertexAttribs4hvNV+26>:   int3
0x4009b697 <glVertexAttribs4hvNV+27>:   int3
0x4009b698 <glVertexAttribs4hvNV+28>:   int3
0x4009b699 <glVertexAttribs4hvNV+29>:   int3
0x4009b69a <glVertexAttribs4hvNV+30>:   int3

(gdb) info registers
eax            0x4009b69d       1074378397
ecx            0x402aee00       1076555264
edx            0x927    2343
ebx            0x40b7fb40       1085799232
esp            0xbffff788       0xbffff788
ebp            0xbffff7a8       0xbffff7a8
esi            0x4009b69c       1074378396
edi            0xbffff85c       -1073743780
eip            0x4009b6a0       0x4009b6a0
eflags         0x210202 2163202
cs             0x73     115
ss             0x7b     123
ds             0x7b     123
es             0x7b     123
fs             0x0      0
gs             0x33     51

(gdb) info shared
From        To          Syms Read   Shared Object Library
0x4004abb0  0x4007a4da  Yes         /usr/X11R6/lib/libGL.so.1
0x400da180  0x40136b60  Yes         /usr/lib/libstdc++.so.5
0x4015c530  0x40174020  Yes         /lib/tls/libm.so.6
0x4017c810  0x40181b20  Yes         /lib/libgcc_s.so.1
0x40199760  0x40291168  Yes         /lib/tls/libc.so.6
0x402b9eb0  0x402badc0  Yes         /lib/tls/libdl.so.2
0x403708c0  0x40936afc  Yes         /usr/lib/libGLcore.so.1
0x40a0d310  0x40a0d368  Yes         /usr/lib/tls/libnvidia-tls.so.1
0x40a12990  0x40a1c490  Yes         /usr/X11R6/lib/libXext.so.6
0x40a2f4a0  0x40a9fa20  Yes         /usr/X11R6/lib/libX11.so.6
0x40000c00  0x40011eaf  Yes         /lib/ld-linux.so.2
0x40b7e780  0x40b7e940  Yes         ./dso.so

(gdb) quit
The program is running.  Exit anyway? (y or n) y

all: test dso.so

test: test.o
        g++ $+ -lGL -o $@

dso.so: dso.o
        g++ -shared $+ -o $@ # linker-script   # -Wl,-Bsymbolic

dso.o : dso.cpp
        g++ -fPIC -Wall -g -c $< -o $@

%.o : %.cpp
        g++ -Wall -g -c $< -o $@


clean:
        rm -f $(shell find . -name "*~")
        rm -f $(shell find . -name "test")
        rm -f $(shell find . -name "*.o")
        rm -f $(shell find . -name "*.so")

#include <stdio.h>
#define GLX_GLXEXT_LEGACY
#include <GL/glx.h>


PFNGLACTIVESTENCILFACEEXTPROC glActiveStencilFaceEXT=NULL;


extern "C" void GetRenderer()
{
    printf("1: Beginning...\n");
    
glActiveStencilFaceEXT=(PFNGLACTIVESTENCILFACEEXTPROC)glXGetProcAddressARB((const
 GLubyte*)"glActiveStencilFaceEXT");
    printf("2: glActiveStencilFaceEXT = %p\n", glActiveStencilFaceEXT);
    if (glActiveStencilFaceEXT!=NULL) glActiveStencilFaceEXT(GL_FRONT);
    printf("3: Still here? (I never see this on my machine.)\n");
}

VERSION { MyVersion { global: GetRenderer; local: *; }; }

#include <stdio.h>
#include <dlfcn.h>


extern "C" { typedef void (*GetRendererT)(); }


int main(int ArgC, const char* ArgV[])
{
    void* RendererDLL=dlopen("./dso.so", RTLD_NOW);
    if (!RendererDLL) { printf("%s\n", dlerror()); return 1; }

    GetRendererT GetRenderer=(GetRendererT)dlsym(RendererDLL, "GetRenderer");
    if (!GetRenderer) { printf("Could not get the address of the GetRenderer() 
function.\n"); dlclose(RendererDLL); return 1; }

    GetRenderer();

    printf("Success!\n");
    dlclose(RendererDLL);
    return 0;
}