[LLVMdev] Unable to call a function in GDB when build with -fPIE

[Karthik Bhat]

Hi All,
I compiled the following code on my linux PC using clang with PIE option-

struct  struct4 {char a; char b; char c; char d; };
struct  struct4  foo4 = {'a','2','c','4'};
struct struct4  fun4()
{
  return foo4;
}

int main()
{
 fun4();
 return 0;
}


> clang -g -fPIE  structs.c

In GDB session when i call p/c fun4() i get something like below-
(gdb) p/c fun4()
Cannot access memory at address 0x34633261

Disassemble of the code is as follows -

(gdb) disassemble
Dump of assembler code for function fun4:
   0x080483e0 <+0>:	call   0x80483e5 <fun4+5>
   0x080483e5 <+5>:	pop    %eax
   0x080483e6 <+6>:	add    $0x1c0f,%eax
   0x080483ec <+12>:	mov    0x4(%esp),%ecx
   0x080483f0 <+16>:	mov    -0x8(%eax),%eax
   0x080483f6 <+22>:	mov    (%eax),%eax
=> 0x080483f8 <+24>:	mov    %eax,(%ecx)
   0x080483fa <+26>:	ret    $0x4
End of assembler dump.
(gdb) i r
eax            0x34633261	878916193
ecx            0xbffff128	-1073745624
edx            0xbffff164	-1073745564
ebx            0x8049ff4	134520820
esp            0xbffff11c	0xbffff11c
ebp            0xbffff138	0xbffff138
esi            0x0	0
edi            0x0	0
eip            0x80483f8	0x80483f8 <fun4+24>
eflags         0x212	[ AF IF ]
cs             0x73	115
ss             0x7b	123
ds             0x7b	123
es             0x7b	123
fs             0x0	0
gs             0x33	51


Seems value in EAX register is getting corrupted in this case. Could
anyone guide me how i can fix this issue.

Regards
Karthik