Yasm supports RIP-relative addressing as well and "wrt ..gotpcrel" is used for this purpose.
It seems that NASM does not recognize "rip" and does not support the "wrt ..gotpcrel" relocation type, either.
Is there any way to do the RIP-relative addressing like this in NASM 64-bit?
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GAS supports RIP-relative reference to a linker-generated symbol pointer.
example code from "AMD64 ABI Draft 0.99":
C source Assembly Code
extern int src[655356]; .extern src
extern int dst[65536]; .extern dst
extern int *ptr; .extern ptr
static int lsrc [65536]; .local lsrc
static int ldst [65536]; .comm lsrc, 2621444,4
static int *lptr; .local ldst
.comm ldst, 2621444,4
.local lptr
.comm lptr,8,8
.text
dst[0] = src[0]; movq src@GOTPCREL(%rip), %rax
movl (%rax), %edx
movq dst@GOTPCREL(%rip), %rax
movl %edx, (%rax)
ptr = dst; movq ptr@GOTPCREL(%rip), %rax
movq dst@GOTPCREL(%rip), %rdx
movq %rdx, (%rax)
*ptr = src[0]; movq ptr@GOTPCREL(%rip), %rax
movq (%rax) %rdx
movq src@GOTPCREL(%rip), %rax
movl (%rax), %eax
movl %eax, (%rdx)
ldst[0] = lsrc[0]; movl lsrc(%rip), %eax
movl %eax, ldst(%rip)
lptr = ldst; lea ldst(%rip), %rdx
movq %rdx, lptr(%rip)
*lptr = lsrc[0]; movq lptr(%rip), %rax
movl lsrc(%rip), %edx
movl %edx, (%rax)
Yasm supports RIP-relative addressing as well and "wrt ..gotpcrel" is used for this purpose.
It seems that NASM does not recognize "rip" and does not support the "wrt ..gotpcrel" relocation type, either.
Is there any way to do the RIP-relative addressing like this in NASM 64-bit?
Oops... for some reason, it got totally messed up when I posted my question. I retype the code to make it easier to read.
< C source >
extern int src[655356];
extern int dst[65536];
extern int *ptr;
static int lsrc [65536];
static int ldst [65536];
static int *lptr;
dst[0] = src[0];
ptr = dst;
*ptr = src[0];
ldst[0] = lsrc[0];
lptr = ldst;
*lptr = lsrc[0];
< Assembly code >
.extern src
.extern dst
.extern ptr
.local lsrc
.comm lsrc, 2621444,4
.local ldst
.comm ldst, 2621444,4
.local lptr
.comm lptr,8,8
.text
movq src@GOTPCREL(%rip), %rax
movl (%rax), %edx
movq dst@GOTPCREL(%rip), %rax
movl %edx, (%rax)
movq ptr@GOTPCREL(%rip), %rax
movq dst@GOTPCREL(%rip), %rdx
movq %rdx, (%rax)
movq ptr@GOTPCREL(%rip), %rax
movq (%rax) %rdx
movq src@GOTPCREL(%rip), %rax
movl (%rax), %eax
movl %eax, (%rdx)
movl lsrc(%rip), %eax
movl %eax, ldst(%rip)
lea ldst(%rip), %rdx
movq lptr(%rip), %rax
movl lsrc(%rip), %edx
movl %edx, (%rax)
I would like to know how I can do the same thing in NASM 64-bit.
Help me!!
The syntax is:
mov rax,[rel foo wrt ..got]
(with the "rel" bit optional if you specify "default rel".)
However, I just tested it and found that it doesn't actually work right. Instead we get the bogus error:
gotpcrel.asm:3: error: ELF format cannot produce PC-relative GOT references
I'll put that on the short list of things to do.
This would have better been filed as a bug report... we'd probably have seen it sooner.
Code for this is in 2.06rc1.