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Pointer arithmetic affects the alignment factor

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Closes #1528
This commit is contained in:
LemonBoy 2019-12-20 10:48:03 +01:00
parent 02ace4569e
commit e134e6c994
3 changed files with 52 additions and 11 deletions
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4
lib/std/start.zig
View File

@ -142,14 +142,14 @@ fn posixCallMainAndExit() noreturn {
const argc = starting_stack_ptr[0];
const argv = @ptrCast([*][*:0]u8, starting_stack_ptr + 1);
const envp_optional = @ptrCast([*:null]?[*:0]u8, argv + argc + 1);
const envp_optional = @ptrCast([*:null]?[*:0]u8, @alignCast(@alignOf(usize), argv + argc + 1));
var envp_count: usize = 0;
while (envp_optional[envp_count]) |_| : (envp_count += 1) {}
const envp = @ptrCast([*][*:0]u8, envp_optional)[0..envp_count];
if (builtin.os == .linux) {
// Find the beginning of the auxiliary vector
const auxv = @ptrCast([*]std.elf.Auxv, envp.ptr + envp_count + 1);
const auxv = @ptrCast([*]std.elf.Auxv, @alignCast(@alignOf(usize), envp.ptr + envp_count + 1));
std.os.linux.elf_aux_maybe = auxv;
// Initialize the TLS area
const gnu_stack_phdr = std.os.linux.tls.initTLS() orelse @panic("ELF missing stack size");

43
src/ir.cpp
View File

@ -15776,19 +15776,44 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
return ir_const_undef(ira, &instruction->base, op1->value->type);
}
// NOTE: this variable is meaningful iff op2_val is not null!
uint64_t byte_offset;
if (op2_val != nullptr) {
uint64_t elem_offset;
if (!ir_resolve_usize(ira, casted_op2, &elem_offset))
return ira->codegen->invalid_instruction;
ZigType *elem_type = op1->value->type->data.pointer.child_type;
if ((err = type_resolve(ira->codegen, elem_type, ResolveStatusSizeKnown)))
return ira->codegen->invalid_instruction;
byte_offset = type_size(ira->codegen, elem_type) * elem_offset;
}
// Fast path for cases where the RHS is zero
if (op2_val != nullptr && byte_offset == 0) {
return op1;
}
ZigType *result_type = op1->value->type;
// The resulting pointer may not be aligned anymore
if (op2_val != nullptr) {
uint32_t align_bytes;
if ((err = resolve_ptr_align(ira, op1->value->type, &align_bytes)))
return ira->codegen->invalid_instruction;
if (byte_offset != 0 && byte_offset % align_bytes != 0)
result_type = adjust_ptr_align(ira->codegen, result_type, 1);
} else {
// The addend is not a comptime-known value
result_type = adjust_ptr_align(ira->codegen, result_type, 1);
}
if (op2_val != nullptr && op1_val != nullptr &&
(op1->value->data.x_ptr.special == ConstPtrSpecialHardCodedAddr ||
op1->value->data.x_ptr.special == ConstPtrSpecialNull))
{
uint64_t start_addr = (op1_val->data.x_ptr.special == ConstPtrSpecialNull) ?
0 : op1_val->data.x_ptr.data.hard_coded_addr.addr;
uint64_t elem_offset;
if (!ir_resolve_usize(ira, casted_op2, &elem_offset))
return ira->codegen->invalid_instruction;
ZigType *elem_type = op1_val->type->data.pointer.child_type;
if ((err = type_resolve(ira->codegen, elem_type, ResolveStatusSizeKnown)))
return ira->codegen->invalid_instruction;
uint64_t byte_offset = type_size(ira->codegen, elem_type) * elem_offset;
uint64_t new_addr;
if (op_id == IrBinOpAdd) {
new_addr = start_addr + byte_offset;
@ -15797,7 +15822,7 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
} else {
zig_unreachable();
}
IrInstruction *result = ir_const(ira, &instruction->base, op1_val->type);
IrInstruction *result = ir_const(ira, &instruction->base, result_type);
result->value->data.x_ptr.special = ConstPtrSpecialHardCodedAddr;
result->value->data.x_ptr.mut = ConstPtrMutRuntimeVar;
result->value->data.x_ptr.data.hard_coded_addr.addr = new_addr;
@ -15806,7 +15831,7 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
IrInstruction *result = ir_build_bin_op(&ira->new_irb, instruction->base.scope,
instruction->base.source_node, op_id, op1, casted_op2, true);
result->value->type = op1->value->type;
result->value->type = result_type;
return result;
}

16
test/stage1/behavior/pointers.zig
View File

@ -288,3 +288,19 @@ test "pointer to array at fixed address" {
// Silly check just to reference `array`
expect(@ptrToInt(&array[0]) == 0x10);
}
test "pointer arithmetic affects the alignment" {
var arr: [10]u8 align(2) = undefined;
var x: usize = 1;
const ptr = @as([*]u8, &arr);
expect(@typeInfo(@TypeOf(ptr)).Pointer.alignment == 2);
const ptr1 = ptr + 1;
expect(@typeInfo(@TypeOf(ptr1)).Pointer.alignment == 1);
const ptr2 = ptr + 4;
expect(@typeInfo(@TypeOf(ptr2)).Pointer.alignment == 2);
const ptr3 = ptr + 0;
expect(@typeInfo(@TypeOf(ptr3)).Pointer.alignment == 2);
const ptr4 = ptr + x;
expect(@typeInfo(@TypeOf(ptr4)).Pointer.alignment == 1);
}