llvm dev - Nov 2012 - [LLVMdev] Failure while calling a function in GDB session

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 as a result of 
mov    (%eax),%eax Call.
 Could anyone guide me how i can fix this issue and which part of code to look
into.

Thanks 
Karthik

Hi Guys any inputs on this issue?

On Fri, Nov 16, 2012 at 8:29 PM, KARTHIKVENKATESH BHAT
<kv.bhat at samsung.com> wrote:
> 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 as a result
of
> mov    (%eax),%eax Call.
>  Could anyone guide me how i can fix this issue and which part of code to
look into.
>
> Thanks
> Karthik
>
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