http://d.puremagic.com/issues/show_bug.cgi?id=4583
Summary: PIC code not working: EBX register set incorrectly Product: D Version: D2 Platform: Other OS/Version: Linux Status: NEW Severity: major Priority: P2 Component: DMD AssignedTo: nob...@puremagic.com ReportedBy: johannesp...@gmail.com --- Comment #0 from Johannes Pfau <johannesp...@gmail.com> 2010-08-05 02:30:57 PDT --- Mostly copy and pasting from an old post in the newsgroup. I tried to build druntime as a shared library and encountered this bug. I tried to reduce it to a simpler testcase, but that didn't work. To reproduce: Download the druntime shared library makefile (so.mak) from this site: http://www.curoles.com/j/dso/dso.html (at the bottom of the page) and compile druntime with it. Compile this very simple test program, as described at the top of that page. ---- void main(){ } ---- The problem seems to be in the assembler code generated for main: http://www.dsource.org/projects/druntime/browser/trunk/src/rt/dmain2.d : extern (C) int main(int argc, char **argv) --------------------------------------- (gdb) disassemble 0xb7f9f36c Dump of assembler code for function main: #ebx=0xb7f16ff4 ebp=0xbffff0a8 0xb7f9f338 <+0>: push %ebp 0xb7f9f339 <+1>: mov %esp,%ebp 0xb7f9f33b <+3>: sub $0x3c,%esp 0xb7f9f33e <+6>: push %ebx #ebx=0xb7f16ff4 0xb7f9f33f <+7>: mov 0xc(%ebp),%ebx 0xb7f9f342 <+10>: push %esi #ebx=0xbffff154 0xb7f9f343 <+11>: push %edi 0xb7f9f344 <+12>: call 0xb7f9f349 <main+17> 0xb7f9f349 <+17>: pop %eax 0xb7f9f34a <+18>: add $0x15343,%eax 0xb7f9f34f <+23>: mov %eax,-0x38(%ebp) 0xb7f9f352 <+26>: movl $0x0,-0x34(%ebp) 0xb7f9f359 <+33>: movl $0x0,-0x30(%ebp) 0xb7f9f360 <+40>: movl $0x0,-0x2c(%ebp) 0xb7f9f367 <+47>: call 0xb7f8813c <_STI_monitor_staticctor at plt> --------------------------------------- (gdb) disassemble '_STI_monitor_staticctor at plt' Dump of assembler code for function _STI_monitor_staticctor at plt: 0xb7f8813c <+0>: jmp *0x2b4(%ebx) -->Segfault here 0xb7f88142 <+6>: push $0x550 0xb7f88147 <+11>: jmp 0xb7f8768c -------------------------------------- The problem is the ebx register. If I understood elf files correctly, the ebx register must hold the address of the GOT when calling a PLT entry. I guess when the main function is called by libc, ebx should be set correctly, in this case to 0xb7f16ff4. I also guess the "push %ebx" instruction is meant to save the GOT adress to stack, because ebx is used for other stuff. But the ebx register is not restored to the GOT address before calling <_STI_monitor_staticctor at plt> and therefore "*jmp 0x2b4(%ebx) " crashes. So this seems to be a problem with dmds PIC support / -fPIC switch. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------