> I would expect that this function below would be naked and just does a add
> and jmp call
Unless you compile with optimizations on, all C function push the stack base
pointer on the stack on function entry (ebp), then save the stack pointer (esp)
in ebp then do the function. Compile with optimizations, in particular
`-fomit-stack-pointer` if you want to avoid the extra save/restore.
> Nim identifiers in asm
The ASM statement doesn't support string interpolation, you need to build the
string via a macro or use GCC syntax
Macro
import macros, strutils
macro myASMStmt(myAddr: static int): untyped =
result = nnkAsmStmt.newTree(
newEmptyNode(),
newLit "jmp 0x" & toHex(myAddr)
)
echo result.toStrLit
const myaddr = 0x123456
proc foo() =
myASMStmt(myaddr)
Run
GCC, use the immediate syntax
proc bar() =
asm """
jmp %[offset]
:
: [offset] "i" (`myaddr`)
:
"""
Run
If you want concrete standalone example of Nim ASM:
Experiments on bigint addition:
*
[https://github.com/mratsim/finite-fields/blob/ab033bb5/add_carry.nim#L73-L113](https://github.com/mratsim/finite-fields/blob/ab033bb5/add_carry.nim#L73-L113)
A macro assembler to ease usage of assembly in Nim (living in a branch for now):
*
[https://github.com/mratsim/constantine/blob/5b538d4e/constantine/primitives/macro_assembler_x86.nim](https://github.com/mratsim/constantine/blob/5b538d4e/constantine/primitives/macro_assembler_x86.nim)
Concrete usages of the macro assembler (note like Intel syntax it's (dst,
operands) order:
*
[https://github.com/mratsim/constantine/blob/5b538d4e/constantine/arithmetic/finite_fields_asm_x86.nim](https://github.com/mratsim/constantine/blob/5b538d4e/constantine/arithmetic/finite_fields_asm_x86.nim)
