ringabout
commented
10 months ago !nim c
import strutils
const
nim_v2 = (NimMajor, NimMinor) > (1, 6)
noExplicitVarDeref = defined(cpp) or nim_v2
func ccopy_x86_asm(ctl: uint64, x: var uint64, y: uint64) =
when noExplicitVarDeref:
asm """
testq %[ctl], %[ctl]
cmovnzq %[y], %[x]
: [x] "+r" (`x`)
: [ctl] "r" (`ctl`), [y] "r" (`y`)
: "cc"
"""
else:
asm """
testq %[ctl], %[ctl]
cmovnzq %[y], %[x]
: [x] "+r" (*`x`)
: [ctl] "r" (`ctl`), [y] "r" (`y`)
: "cc"
"""
func ccopy_x86_emit(ctl: uint64, x: var uint64, y: uint64) =
when noExplicitVarDeref:
{.emit:[
"""
asm volatile(
"testq %[ctl], %[ctl]\n"
"cmovnzq %[y], %[x]\n"
: [x] "+r" (""", x, """)
: [ctl] "r" (""", ctl, """), [y] "r" (""", y, """)
: "cc"
);"""].}
else:
{.emit:[
"""
asm volatile(
"testq %[ctl], %[ctl]\n"
"cmovnzq %[y], %[x]\n"
: [x] "+r" (*""", x, """)
: [ctl] "r" (""", ctl, """), [y] "r" (""", y, """)
: "cc"
);"""].}
let x = 0x1111111'u64
let y = 0xFFFFFFF'u64
block:
let ctl = 1'u64
var a0 = x
ctl.ccopy_x86_asm(a0, y)
var a1 = x
ctl.ccopy_x86_emit(a1, y)
echo "a0: ", a0.toHex()
echo "a1: ", a1.toHex()
doAssert a0 == a1
block:
let ctl = 0'u64
var a0 = x
ctl.ccopy_x86_asm(a0, y)
var a1 = x
ctl.ccopy_x86_emit(a1, y)
echo "a0: ", a0.toHex()
echo "a1: ", a1.toHex()
doAssert a0 == a1
github-actions[bot]
metagn
Before Nim v2, interpolating a
varparameter:This was the case for both
asmandemitstatements.Following Nim v2:
Test case:
Output matrix
Expected output:
Incorrect:
and that's not taking into account overriding the
varpointer, which might lead to writing to random location.Suggested solution ASM should also auto-deref var pointers.
Note The fix can probably address https://github.com/nim-lang/Nim/issues/18133 in one fell swoop.