How can I get correct function address on Aix? - gcc

Question

see a simple code below:
int foo(int a)
{
return a;
}
int main() {
printf("%x\n", foo);
printf("%x\n", &foo);
printf("%x\n", *foo);
foo(1);
}
They all displayed the same value:
0x20453840
0x20453840
0x20453840
I used gdb to check foo() entry point is:
(gdb) p foo
$1 = {int (int)} 0x100003d8 <foo>
the value 0x20453840 is actually foo() pointer of pointer:
(gdb) p /x *0x20453850
$3 = 0x100003d8
(gdb) si
0x10000468 76 foo(1);
0x10000464 <main+76>: 38 60 00 01 li r3,1
=> 0x10000468 <main+80>: 4b ff ff 71 bl 0x100003d8 <foo>
(gdb)
foo (a=541407312) at insertcode.c:57
57 {
=> 0x100003d8 <foo+0>: 93 e1 ff fc stw r31,-4(r1)
0x100003dc <foo+4>: 94 21 ff e0 stwu r1,-32(r1)
0x100003e0 <foo+8>: 7c 3f 0b 78 mr r31,r1
0x100003e4 <foo+12>: 90 7f 00 38 stw r3,56(r31)
(gdb)
So I think 0x100003d8 is the entry point.
I used gcc 4.6.2 to compile.
I have tow questions:
why different function address definition on AIX? is it related to gcc?
I have to use gcc not xlC.
how to get real function address in C on AIX?
Thanks in advance!

Answer 1

why different function address definition on AIX?
nm -Pg ./f_addr | grep foo
Try this command, and you will see you have too symbols: foo and .foo One of them lives in the code segment (or text segment), the other, in the data segment.
The purpose is, indeed, creating an indirection in function calling; it is important when creating/using shared libraries.
is it related to gcc? I have to use gcc not xlC.
No.
How to get real function address in C on AIX?
Please clarify your question: what do you want to do with the 'real address'.