https://sourceware.org/bugzilla/show_bug.cgi?id=17567
Bug ID: 17567
Summary: RIP Relative Addressing fails on macho64 format
Product: binutils
Version: 2.24
Status: NEW
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: bmpotter13 at gmail dot com
I am using binutils 2.24 to try to write a string to standard out of screen.
Macho-64 does not support assignment of 32 bit absolute addresses. A working
solution is to use RIP relative addressing.
Using the following:
movq msg, %rdi
...
msg: .ascii "Hello\n"
it generates the error "write64bit.s:6: Error: cannot represent relocation type
BFD_RELOC_X86_64_32S"
while the following
leaq msg(%rip), %rdi
...
msg: .ascii "Hello\n"
generates no errors, assembles, and links without errors.
Using 2.24 'as', this produces "leaq 0x0(%rip), %rdi" rather than "leaq
0x13(%rip), %rdi" as shown from the objdump disassembly.
Disassembly of section .text:
0000000000001fcd <_main>:
1fcd: b8 04 00 00 02 mov $0x2000004,%eax
1fd2: 48 c7 c7 01 00 00 00 mov $0x1,%rdi
1fd9: 48 8d 35 00 00 00 00 lea 0x0(%rip),%rsi # 1fe0
<_main+0x13>
1fe0: 48 c7 c2 0d 00 00 00 mov $0xd,%rdx
1fe7: 0f 05 syscall
1fe9: b8 01 00 00 02 mov $0x2000001,%eax
1fee: 48 31 ff xor %rdi,%rdi
1ff1: 0f 05 syscall
The source code assembles correctly using the 1.38 provided by Xcode.
I compiled from source using:
~/Downloads/binutils-2.24/configure --disable-werror
make
~/Downloads/binutils-2.24/gas/configure
make
sudo make install
Assembled and linked with
as -o write64bit.o write64bit.s
ld -lSystem -macosx_version_min 10.10 -o write64bit write64bit.o
write64bit.s source code
.global _main
_main:
movl $0x2000004, %eax
movq $1, %rdi
leaq msg(%rip), %rsi
movq $0xd, %rdx
syscall
movl $0x2000001, %eax
xorq %rdi, %rdi
syscall
msg: .ascii "Hello world!\n"
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