Comments (2)
You can query the location of a previously defined label via Assembler::labels()
which returns a LabelRegistry
. From that you can use LabelRegistry::resolve_static(StaticLabel::Global("yourlabel"))
to get the offset of that label location into the assembling buffer. The absolute address of the label is then the base address of the assembling buffer plus the label offset.
This of course only works if the global label has already been defined in the code before calling this method. And it'll go stale if the buffer needs to be relocated.
Right now there's indeed no support for putting the absolute label address directly in the code stream, especially if such a label is only defined afterwards. Such a feature would also need to use proper relocations if the assembling buffer needed to be moved or resized. Likely the best way to handle this is some kind of directive. But even then it'd be tricky with tagged pointers. I think it could work as long as the tags are simply added to the pointer as relocating them is essentially current_value - old_base_address + new_base_address.
from dynasm-rs.
Thanks for the quick feedback!
Right now there's indeed no support for putting the absolute label address directly in the code stream ... Such a feature would also need to use proper relocations if the assembling buffer needed to be moved or resized
Yes, that's what I was looking for, basically the same way nasm/llvm ir etc would do it. Your relocation math would work fine. I wasn't quite sure if it was implemented or not, since I did see various relocation types like RelToAbs in the code. I'll find another way to do what I need, thanks again.
foo:
mov rax, bar + 1
bar:
dq $10
nasm -f elf64 test.s
0000000000000000 <foo>:
0: 48 b8 00 00 00 00 00 movabs $0x0,%rax
7: 00 00 00
readelf -r test.o
Relocation section '.rela.text' at offset 0x2a0 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000000002 000200000001 R_X86_64_64 0000000000000000 .text + b
from dynasm-rs.
Related Issues (20)
- Feature request: compile-time resolution of "super-local" label HOT 5
- Language dialect reference for AArch64 has some stale x86/x86-64 references HOT 2
- omit known zero offset HOT 2
- Consider using `MAP_JIT` on macOS HOT 1
- Link to GitHub pages is broken HOT 3
- Question: dynamically replacing code while running it HOT 4
- Executable buffer relocations HOT 5
- ImpossibleRelocation error on seemingly valid AArch64 code HOT 4
- Aarch64: mov w0, immu32 expects a u64 when encoded at runtime
- Aarch64: dynamic registers prevent immediates HOT 2
- Symbols for dynamic labels HOT 6
- Improve documentation of `ExecutableBuffer::ptr`. HOT 2
- Mismatched type error when writing generic code HOT 2
- Dynamic Memory Operands HOT 3
- Handling out-of-bounds AArch64 immediates HOT 1
- Label clarifications HOT 3
- Arch::name() unused. HOT 2
- Can't run `cargo doc` using stable rust? HOT 1
- Precedence issue when using typemapped operands in x64 mode HOT 2
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from dynasm-rs.