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Fix UB in 128 bit cttz/ctlz intrinsics #672

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Fix UB in 128 bit cttz/ctlz intrinsics #672

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49 changes: 49 additions & 0 deletions src/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -444,6 +444,55 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
);
result.to_rvalue()
}
/// Performs a *bitcount* intrinsic on a given arg, properly handling the zero case.
pub fn checked_bitcount_intrinsic(
&mut self,
name: rustc_span::Symbol,
arg: RValue<'gcc>,
width: u64,
) -> RValue<'gcc> {
// For u/i128, the algorithm implementing `ctlz`/`cttz` already handles the 0 case, by handling it for each half.
if width == 128 {
return match name {
sym::ctlz => self.count_leading_zeroes(width, arg),
sym::cttz => self.count_trailing_zeroes(width, arg),
_ => unreachable!(),
};
}
use rustc_span::sym;
let func = self.current_func.borrow().expect("func");
let then_block = func.new_block("then");
let else_block = func.new_block("else");
let after_block = func.new_block("after");

let result = func.new_local(None, self.u32_type, "zeros");
let zero = self.cx.gcc_zero(arg.get_type());
let cond = self.gcc_icmp(IntPredicate::IntEQ, arg, zero);
self.llbb().end_with_conditional(None, cond, then_block, else_block);

let zero_result = self.cx.gcc_uint(self.u32_type, width);
then_block.add_assignment(None, result, zero_result);
then_block.end_with_jump(None, after_block);

// NOTE: since jumps were added in a place
// count_leading_zeroes() does not expect, the current block
// in the state need to be updated.
self.switch_to_block(else_block);

let zeros = match name {
sym::ctlz => self.count_leading_zeroes(width, arg),
sym::cttz => self.count_trailing_zeroes(width, arg),
_ => unreachable!(),
};
self.llbb().add_assignment(None, result, zeros);
self.llbb().end_with_jump(None, after_block);

// NOTE: since jumps were added in a place rustc does not
// expect, the current block in the state need to be updated.
self.switch_to_block(after_block);

result.to_rvalue()
}
}

impl<'tcx> HasTyCtxt<'tcx> for Builder<'_, '_, 'tcx> {
Expand Down
55 changes: 12 additions & 43 deletions src/intrinsic/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -224,39 +224,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tc
match int_type_width_signed(ty, self) {
Some((width, signed)) => match name {
sym::ctlz | sym::cttz => {
let func = self.current_func.borrow().expect("func");
let then_block = func.new_block("then");
let else_block = func.new_block("else");
let after_block = func.new_block("after");

let arg = args[0].immediate();
let result = func.new_local(None, self.u32_type, "zeros");
let zero = self.cx.gcc_zero(arg.get_type());
let cond = self.gcc_icmp(IntPredicate::IntEQ, arg, zero);
self.llbb().end_with_conditional(None, cond, then_block, else_block);

let zero_result = self.cx.gcc_uint(self.u32_type, width);
then_block.add_assignment(None, result, zero_result);
then_block.end_with_jump(None, after_block);

// NOTE: since jumps were added in a place
// count_leading_zeroes() does not expect, the current block
// in the state need to be updated.
self.switch_to_block(else_block);

let zeros = match name {
sym::ctlz => self.count_leading_zeroes(width, arg),
sym::cttz => self.count_trailing_zeroes(width, arg),
_ => unreachable!(),
};
self.llbb().add_assignment(None, result, zeros);
self.llbb().end_with_jump(None, after_block);

// NOTE: since jumps were added in a place rustc does not
// expect, the current block in the state need to be updated.
self.switch_to_block(after_block);

result.to_rvalue()
self.checked_bitcount_intrinsic(name, args[0].immediate(), width)
}
sym::ctlz_nonzero => self.count_leading_zeroes(width, args[0].immediate()),
sym::cttz_nonzero => self.count_trailing_zeroes(width, args[0].immediate()),
Expand Down Expand Up @@ -712,7 +680,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
self.gcc_int_cast(result, result_type)
}

fn count_leading_zeroes(&mut self, width: u64, arg: RValue<'gcc>) -> RValue<'gcc> {
pub fn count_leading_zeroes(&mut self, width: u64, arg: RValue<'gcc>) -> RValue<'gcc> {
// TODO(antoyo): use width?
let arg_type = arg.get_type();
let result_type = self.u32_type;
Expand Down Expand Up @@ -743,15 +711,16 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
let one = self.context.new_rvalue_one(self.usize_type);
let two = self.context.new_rvalue_from_long(self.usize_type, 2);

let clzll = self.context.get_builtin_function("__builtin_clzll");

let first_elem = self.context.new_array_access(None, result, zero);
let first_value = self.gcc_int_cast(self.context.new_call(None, clzll, &[high]), arg_type);
let high_ctlz = self.checked_bitcount_intrinsic(sym::ctlz, high, 64);
let first_value = self.gcc_int_cast(high_ctlz, arg_type);
self.llbb()
.add_assignment(self.location, first_elem, first_value);

let second_elem = self.context.new_array_access(self.location, result, one);
let cast = self.gcc_int_cast(self.context.new_call(self.location, clzll, &[low]), arg_type);

let low_ctlz = self.checked_bitcount_intrinsic(sym::ctlz,low,64 );
let cast = self.gcc_int_cast(low_ctlz, arg_type);
let second_value = self.add(cast, sixty_four);
self.llbb()
.add_assignment(self.location, second_elem, second_value);
Expand Down Expand Up @@ -788,7 +757,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
self.context.new_cast(self.location, res, result_type)
}

fn count_trailing_zeroes(&mut self, _width: u64, arg: RValue<'gcc>) -> RValue<'gcc> {
pub fn count_trailing_zeroes(&mut self, _width: u64, arg: RValue<'gcc>) -> RValue<'gcc> {
let arg_type = arg.get_type();
let result_type = self.u32_type;
let arg = if arg_type.is_signed(self.cx) {
Expand Down Expand Up @@ -826,15 +795,15 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
let one = self.context.new_rvalue_one(self.usize_type);
let two = self.context.new_rvalue_from_long(self.usize_type, 2);

let ctzll = self.context.get_builtin_function("__builtin_ctzll");

let first_elem = self.context.new_array_access(self.location, result, zero);
let first_value = self.gcc_int_cast(self.context.new_call(self.location, ctzll, &[low]), arg_type);
let low_ctzll = self.checked_bitcount_intrinsic(sym::cttz,low , 64);
let first_value = self.gcc_int_cast(low_ctzll, arg_type);
self.llbb()
.add_assignment(self.location, first_elem, first_value);

let second_elem = self.context.new_array_access(self.location, result, one);
let second_value = self.gcc_add(self.gcc_int_cast(self.context.new_call(self.location, ctzll, &[high]), arg_type), sixty_four);
let high_ctzll = self.checked_bitcount_intrinsic(sym::cttz,high , 64);
let second_value = self.gcc_add(self.gcc_int_cast(high_ctzll, arg_type), sixty_four);
self.llbb()
.add_assignment(self.location, second_elem, second_value);

Expand Down
4 changes: 3 additions & 1 deletion tests/lang_tests_common.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -115,7 +115,9 @@ pub fn main_inner(profile: Profile) {
}
}
match profile {
Profile::Debug => {}
Profile::Debug => {
compiler.args(["-C", "llvm-args=santize-undefined"]);
}
Profile::Release => {
compiler.args(["-C", "opt-level=3", "-C", "lto=no"]);
}
Expand Down
38 changes: 38 additions & 0 deletions tests/run/bitintrinsics_128.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
// Compiler:
//
// Run-time:

#![feature(no_core, intrinsics)]
#![no_std]
#![no_core]
#![no_main]

extern crate mini_core;
use intrinsics::black_box;
use mini_core::*;

#[rustc_intrinsic]
pub const fn ctlz<T: Copy>(_x: T) -> u32;

#[rustc_intrinsic]
pub const fn cttz<T: Copy>(_x: T) -> u32;

#[no_mangle]
extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
if ctlz(black_box(0_u128)) != 128 {
return 1;
}
if ctlz(black_box(1_u128)) != 127 {
return 2;
}
if cttz(black_box(0_u128)) != 128 {
return 3;
}
if cttz(black_box(1_u128)) != 0 {
return 4;
}
if cttz(black_box(2_u128)) != 1 {
return 4;
}
0
}
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