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fix endianness of sub-byte integer fields in packed structs
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closes #307
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@andrewrk
andrewrk committed Dec 22, 2017
1 parent e44a113 commit 760b307
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Showing 2 changed files with 56 additions and 9 deletions.
40 changes: 31 additions & 9 deletions src/codegen.cpp
View file
Expand Up @@ -1238,11 +1238,13 @@ static LLVMValueRef gen_assign_raw(CodeGen *g, LLVMValueRef ptr, TypeTableEntry
return nullptr;
}

bool big_endian = g->is_big_endian;

LLVMValueRef containing_int = gen_load(g, ptr, ptr_type, "");

uint32_t bit_offset = ptr_type->data.pointer.bit_offset;
uint32_t host_bit_count = LLVMGetIntTypeWidth(LLVMTypeOf(containing_int));
uint32_t shift_amt = host_bit_count - bit_offset - unaligned_bit_count;
uint32_t shift_amt = big_endian ? host_bit_count - bit_offset - unaligned_bit_count : bit_offset;
LLVMValueRef shift_amt_val = LLVMConstInt(LLVMTypeOf(containing_int), shift_amt, false);

LLVMValueRef mask_val = LLVMConstAllOnes(child_type->type_ref);
Expand Down Expand Up @@ -2198,12 +2200,14 @@ static LLVMValueRef ir_render_load_ptr(CodeGen *g, IrExecutable *executable, IrI
if (unaligned_bit_count == 0)
return get_handle_value(g, ptr, child_type, ptr_type);

bool big_endian = g->is_big_endian;

assert(!handle_is_ptr(child_type));
LLVMValueRef containing_int = gen_load(g, ptr, ptr_type, "");

uint32_t bit_offset = ptr_type->data.pointer.bit_offset;
uint32_t host_bit_count = LLVMGetIntTypeWidth(LLVMTypeOf(containing_int));
uint32_t shift_amt = host_bit_count - bit_offset - unaligned_bit_count;
uint32_t shift_amt = big_endian ? host_bit_count - bit_offset - unaligned_bit_count : bit_offset;

LLVMValueRef shift_amt_val = LLVMConstInt(LLVMTypeOf(containing_int), shift_amt, false);
LLVMValueRef shifted_value = LLVMBuildLShr(g->builder, containing_int, shift_amt_val, "");
Expand Down Expand Up @@ -3796,17 +3800,26 @@ static LLVMValueRef pack_const_int(CodeGen *g, LLVMTypeRef big_int_type_ref, Con
case TypeTableEntryIdStruct:
{
assert(type_entry->data.structure.layout == ContainerLayoutPacked);
bool is_big_endian = g->is_big_endian; // TODO get endianness from struct type

LLVMValueRef val = LLVMConstInt(big_int_type_ref, 0, false);
size_t used_bits = 0;
for (size_t i = 0; i < type_entry->data.structure.src_field_count; i += 1) {
TypeStructField *field = &type_entry->data.structure.fields[i];
if (field->gen_index == SIZE_MAX) {
continue;
}
LLVMValueRef child_val = pack_const_int(g, big_int_type_ref, &const_val->data.x_struct.fields[i]);
LLVMValueRef shift_amt = LLVMConstInt(big_int_type_ref, field->packed_bits_size, false);
val = LLVMConstShl(val, shift_amt);
val = LLVMConstOr(val, child_val);
if (is_big_endian) {
LLVMValueRef shift_amt = LLVMConstInt(big_int_type_ref, field->packed_bits_size, false);
val = LLVMConstShl(val, shift_amt);
val = LLVMConstOr(val, child_val);
} else {
LLVMValueRef shift_amt = LLVMConstInt(big_int_type_ref, used_bits, false);
LLVMValueRef child_val_shifted = LLVMConstShl(child_val, shift_amt);
val = LLVMConstOr(val, child_val_shifted);
used_bits += field->packed_bits_size;
}
}
return val;
}
Expand Down Expand Up @@ -3931,20 +3944,29 @@ static LLVMValueRef gen_const_val(CodeGen *g, ConstExprValue *const_val) {
fields[type_struct_field->gen_index] = val;
make_unnamed_struct = make_unnamed_struct || is_llvm_value_unnamed_type(field_val->type, val);
} else {
bool is_big_endian = g->is_big_endian; // TODO get endianness from struct type
LLVMTypeRef big_int_type_ref = LLVMStructGetTypeAtIndex(type_entry->type_ref,
(unsigned)type_struct_field->gen_index);
LLVMValueRef val = LLVMConstInt(big_int_type_ref, 0, false);
size_t used_bits = 0;
for (size_t i = src_field_index; i < src_field_index_end; i += 1) {
TypeStructField *it_field = &type_entry->data.structure.fields[i];
if (it_field->gen_index == SIZE_MAX) {
continue;
}
LLVMValueRef child_val = pack_const_int(g, big_int_type_ref,
&const_val->data.x_struct.fields[i]);
LLVMValueRef shift_amt = LLVMConstInt(big_int_type_ref,
it_field->packed_bits_size, false);
val = LLVMConstShl(val, shift_amt);
val = LLVMConstOr(val, child_val);
if (is_big_endian) {
LLVMValueRef shift_amt = LLVMConstInt(big_int_type_ref,
it_field->packed_bits_size, false);
val = LLVMConstShl(val, shift_amt);
val = LLVMConstOr(val, child_val);
} else {
LLVMValueRef shift_amt = LLVMConstInt(big_int_type_ref, used_bits, false);
LLVMValueRef child_val_shifted = LLVMConstShl(child_val, shift_amt);
val = LLVMConstOr(val, child_val_shifted);
used_bits += it_field->packed_bits_size;
}
}
fields[type_struct_field->gen_index] = val;
}
Expand Down
25 changes: 25 additions & 0 deletions test/cases/struct.zig
View file
Expand Up @@ -379,3 +379,28 @@ const Nibbles = packed struct {
x: u4,
y: u4,
};

const Bitfields = packed struct {
f1: u16,
f2: u16,
f3: u8,
f4: u8,
f5: u4,
f6: u4,
f7: u8,
};

test "native bit field understands endianness" {
var all: u64 = 0x7765443322221111;
var bytes: [8]u8 = undefined;
@memcpy(&bytes[0], @ptrCast(&u8, &all), 8);
var bitfields = *@ptrCast(&Bitfields, &bytes[0]);

assert(bitfields.f1 == 0x1111);
assert(bitfields.f2 == 0x2222);
assert(bitfields.f3 == 0x33);
assert(bitfields.f4 == 0x44);
assert(bitfields.f5 == 0x5);
assert(bitfields.f6 == 0x6);
assert(bitfields.f7 == 0x77);
}

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