问题
The MOV have the two form to move an imm to r64:
| Opcode | Instruction | Op/En | 64-Bit Mode | Compat/Leg Mode | Description |
| REX.W + B8+ rd | MOV r64, imm64 | E | Valid | N.E. | Move imm64 to r64. |
| REX.W + C7 /0 | MOV r/m64,imm32 | F | Valid | N.E. | Move imm32 sign extended to 64-bits to r/m64. |
In the example bellow, Line 6(Line 5,7 are not so important, we ignore it.) use the 2nd form. So the problem is, if we link the object file with '-Ttext=' to specify a address that can be fit in 32bits, e.g. 'ld m.o -Ttext=0x1234' it works well. but if we use an addres wider than 32bits, e.g. 'ld m.o -Ttext=0x1234567887', it does not works.
If Line 6 is encoded in the 1st form, i think the two link command above will both work well.
So how to direct the gas encode the Line 6 in the 1st form?
1
2 .code64
3 .global _start
4 _start:
5 movq $1, %rdi
6 movq $str, %rsi
7 movq $len, %rdx
8 movl $1, %eax
9 syscall
10 movq $0, %rdi
11 movl $60, %eax
12 syscall
13 str: .asciz "hello write\n"
14 .equ len, . - str
# as m.s -o m.o
# ld m.o -Ttext=0x1234
0000000000001234 <_start>:
1234: 48 c7 c7 01 00 00 00 mov $0x1,%rdi
123b: 48 c7 c6 5e 12 00 00 mov $0x125e,%rsi
1242: 48 c7 c2 0d 00 00 00 mov $0xd,%rdx
1249: b8 01 00 00 00 mov $0x1,%eax
124e: 0f 05 syscall
1250: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
1257: b8 3c 00 00 00 mov $0x3c,%eax
125c: 0f 05 syscall
# ld m.o -Ttext=0x1234567887
m.o: In function `_start':
(.text+0xa): relocation truncated to fit: R_X86_64_32S against `.text'
Edit:
I got it. I write a funciton like
long aaa(void)
{
return 0x1234567890l;
}
and the gcc generate following asm code
movabsq $78187493520, %rax
to return the value. My example works int this way now.
But I don't find any thing about 'movabsq' in 'ingo gas'. Somebody tell me where to get the help? Thanks!
来源：https://stackoverflow.com/questions/11341486/how-to-direct-gas-use-a-specified-encoding-form-of-instructions-for-example-mo