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Antoni Boucher 2021-08-12 21:53:49 -04:00
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compiler/rustc_codegen_gcc/src/consts.rs Normal file
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use gccjit::{RValue, Type};
use rustc_codegen_ssa::traits::{BaseTypeMethods, ConstMethods, DerivedTypeMethods, StaticMethods};
use rustc_hir as hir;
use rustc_hir::Node;
use rustc_middle::{bug, span_bug};
use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
use rustc_middle::mir::mono::MonoItem;
use rustc_middle::ty::{self, Instance, Ty};
use rustc_mir::interpret::{self, Allocation, ErrorHandled, Scalar as InterpScalar, read_target_uint};
use rustc_span::Span;
use rustc_span::def_id::DefId;
use rustc_target::abi::{self, Align, HasDataLayout, LayoutOf, Primitive, Size};
use crate::base;
use crate::context::CodegenCx;
use crate::mangled_std_symbols::{ARGC, ARGV, ARGV_INIT_ARRAY};
use crate::type_of::LayoutGccExt;
impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
pub fn const_bitcast(&self, value: RValue<'gcc>, typ: Type<'gcc>) -> RValue<'gcc> {
if value.get_type() == self.bool_type.make_pointer() {
if let Some(pointee) = typ.get_pointee() {
if pointee.is_vector().is_some() {
panic!()
}
}
}
self.context.new_bitcast(None, value, typ)
}
}
impl<'gcc, 'tcx> StaticMethods for CodegenCx<'gcc, 'tcx> {
fn static_addr_of(&self, cv: RValue<'gcc>, align: Align, kind: Option<&str>) -> RValue<'gcc> {
if let Some(global_value) = self.const_globals.borrow().get(&cv) {
// TODO
/*unsafe {
// Upgrade the alignment in cases where the same constant is used with different
// alignment requirements
let llalign = align.bytes() as u32;
if llalign > llvm::LLVMGetAlignment(gv) {
llvm::LLVMSetAlignment(gv, llalign);
}
}*/
return *global_value;
}
let global_value = self.static_addr_of_mut(cv, align, kind);
// TODO
/*unsafe {
llvm::LLVMSetGlobalConstant(global_value, True);
}*/
self.const_globals.borrow_mut().insert(cv, global_value);
global_value
}
fn codegen_static(&self, def_id: DefId, is_mutable: bool) {
let attrs = self.tcx.codegen_fn_attrs(def_id);
let instance = Instance::mono(self.tcx, def_id);
let name = &*self.tcx.symbol_name(instance).name;
let (value, alloc) =
match codegen_static_initializer(&self, def_id) {
Ok(value) => value,
// Error has already been reported
Err(_) => return,
};
let is_tls = attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL);
let global = self.get_static(def_id);
// boolean SSA values are i1, but they have to be stored in i8 slots,
// otherwise some LLVM optimization passes don't work as expected
let val_llty = self.val_ty(value);
let value =
if val_llty == self.type_i1() {
//val_llty = self.type_i8();
unimplemented!();
//llvm::LLVMConstZExt(value, val_llty)
}
else {
value
};
let instance = Instance::mono(self.tcx, def_id);
let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
let gcc_type = self.layout_of(ty).gcc_type(self, true);
let global =
if val_llty == gcc_type {
global
}
else {
// If we created the global with the wrong type,
// correct the type.
/*let name = llvm::get_value_name(global).to_vec();
llvm::set_value_name(global, b"");
let linkage = llvm::LLVMRustGetLinkage(global);
let visibility = llvm::LLVMRustGetVisibility(global);*/
let new_global = self.get_or_insert_global(&name, val_llty, is_tls, attrs.link_section);
/*llvm::LLVMRustSetLinkage(new_global, linkage);
llvm::LLVMRustSetVisibility(new_global, visibility);*/
// To avoid breaking any invariants, we leave around the old
// global for the moment; we'll replace all references to it
// with the new global later. (See base::codegen_backend.)
//self.statics_to_rauw.borrow_mut().push((global, new_global));
new_global
};
// TODO
//set_global_alignment(&self, global, self.align_of(ty));
//llvm::LLVMSetInitializer(global, value);
let value = self.rvalue_as_lvalue(value);
let value = value.get_address(None);
let dest_typ = global.get_type();
let value = self.context.new_cast(None, value, dest_typ);
// NOTE: do not init the variables related to argc/argv because it seems we cannot
// overwrite those variables.
// FIXME: correctly support global variable initialization.
let skip_init = [
ARGV_INIT_ARRAY,
ARGC,
ARGV,
];
if !skip_init.iter().any(|symbol_name| name.starts_with(symbol_name)) {
// TODO: switch to set_initializer when libgccjit supports that.
let memcpy = self.context.get_builtin_function("memcpy");
let dst = self.context.new_cast(None, global, self.type_i8p());
let src = self.context.new_cast(None, value, self.type_ptr_to(self.type_void()));
let size = self.context.new_rvalue_from_long(self.sizet_type, alloc.size().bytes() as i64);
self.global_init_block.add_eval(None, self.context.new_call(None, memcpy, &[dst, src, size]));
}
// As an optimization, all shared statics which do not have interior
// mutability are placed into read-only memory.
if !is_mutable {
if self.type_is_freeze(ty) {
// TODO
//llvm::LLVMSetGlobalConstant(global, llvm::True);
}
}
//debuginfo::create_global_var_metadata(&self, def_id, global);
if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
// Do not allow LLVM to change the alignment of a TLS on macOS.
//
// By default a global's alignment can be freely increased.
// This allows LLVM to generate more performant instructions
// e.g., using load-aligned into a SIMD register.
//
// However, on macOS 10.10 or below, the dynamic linker does not
// respect any alignment given on the TLS (radar 24221680).
// This will violate the alignment assumption, and causing segfault at runtime.
//
// This bug is very easy to trigger. In `println!` and `panic!`,
// the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
// which the values would be `mem::replace`d on initialization.
// The implementation of `mem::replace` will use SIMD
// whenever the size is 32 bytes or higher. LLVM notices SIMD is used
// and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
// which macOS's dyld disregarded and causing crashes
// (see issues #51794, #51758, #50867, #48866 and #44056).
//
// To workaround the bug, we trick LLVM into not increasing
// the global's alignment by explicitly assigning a section to it
// (equivalent to automatically generating a `#[link_section]` attribute).
// See the comment in the `GlobalValue::canIncreaseAlignment()` function
// of `lib/IR/Globals.cpp` for why this works.
//
// When the alignment is not increased, the optimized `mem::replace`
// will use load-unaligned instructions instead, and thus avoiding the crash.
//
// We could remove this hack whenever we decide to drop macOS 10.10 support.
if self.tcx.sess.target.options.is_like_osx {
// The `inspect` method is okay here because we checked relocations, and
// because we are doing this access to inspect the final interpreter state
// (not as part of the interpreter execution).
//
// FIXME: This check requires that the (arbitrary) value of undefined bytes
// happens to be zero. Instead, we should only check the value of defined bytes
// and set all undefined bytes to zero if this allocation is headed for the
// BSS.
/*let all_bytes_are_zero = alloc.relocations().is_empty()
&& alloc
.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len())
.iter()
.all(|&byte| byte == 0);
let sect_name = if all_bytes_are_zero {
CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_bss\0")
} else {
CStr::from_bytes_with_nul_unchecked(b"__DATA,__thread_data\0")
};*/
unimplemented!();
//llvm::LLVMSetSection(global, sect_name.as_ptr());
}
}
// Wasm statics with custom link sections get special treatment as they
// go into custom sections of the wasm executable.
if self.tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
if let Some(_section) = attrs.link_section {
unimplemented!();
/*let section = llvm::LLVMMDStringInContext(
self.llcx,
section.as_str().as_ptr().cast(),
section.as_str().len() as c_uint,
);
assert!(alloc.relocations().is_empty());
// The `inspect` method is okay here because we checked relocations, and
// because we are doing this access to inspect the final interpreter state (not
// as part of the interpreter execution).
let bytes =
alloc.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len());
let alloc = llvm::LLVMMDStringInContext(
self.llcx,
bytes.as_ptr().cast(),
bytes.len() as c_uint,
);
let data = [section, alloc];
let meta = llvm::LLVMMDNodeInContext(self.llcx, data.as_ptr(), 2);
llvm::LLVMAddNamedMetadataOperand(
self.llmod,
"wasm.custom_sections\0".as_ptr().cast(),
meta,
);*/
}
} else {
// TODO
//base::set_link_section(global, &attrs);
}
if attrs.flags.contains(CodegenFnAttrFlags::USED) {
self.add_used_global(global);
}
}
/// Add a global value to a list to be stored in the `llvm.used` variable, an array of i8*.
fn add_used_global(&self, _global: RValue<'gcc>) {
// TODO
//let cast = self.context.new_cast(None, global, self.type_i8p());
//self.used_statics.borrow_mut().push(cast);
}
}
impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
pub fn static_addr_of_mut(&self, cv: RValue<'gcc>, align: Align, kind: Option<&str>) -> RValue<'gcc> {
let (name, gv) =
match kind {
Some(kind) if !self.tcx.sess.fewer_names() => {
let name = self.generate_local_symbol_name(kind);
// TODO: check if it's okay that TLS is off here.
// TODO: check if it's okay that link_section is None here.
// TODO: set alignment here as well.
let gv = self.define_global(&name[..], self.val_ty(cv), false, None).unwrap_or_else(|| {
bug!("symbol `{}` is already defined", name);
});
//llvm::LLVMRustSetLinkage(gv, llvm::Linkage::PrivateLinkage);
(name, gv)
}
_ => {
let index = self.global_gen_sym_counter.get();
let name = format!("global_{}_{}", index, self.codegen_unit.name());
let typ = self.val_ty(cv).get_aligned(align.bytes());
let global = self.define_private_global(typ);
(name, global)
},
};
// FIXME: I think the name coming from generate_local_symbol_name() above cannot be used
// globally.
// NOTE: global seems to only be global in a module. So save the name instead of the value
// to import it later.
self.global_names.borrow_mut().insert(cv, name);
self.global_init_block.add_assignment(None, gv.dereference(None), cv);
//llvm::SetUnnamedAddress(gv, llvm::UnnamedAddr::Global);
gv
}
pub fn get_static(&self, def_id: DefId) -> RValue<'gcc> {
let instance = Instance::mono(self.tcx, def_id);
let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
if let Some(&global) = self.instances.borrow().get(&instance) {
/*let attrs = self.tcx.codegen_fn_attrs(def_id);
let name = &*self.tcx.symbol_name(instance).name;
let name =
if let Some(linkage) = attrs.linkage {
// This is to match what happens in check_and_apply_linkage.
Cow::from(format!("_rust_extern_with_linkage_{}", name))
}
else {
Cow::from(name)
};
let global = self.context.new_global(None, GlobalKind::Imported, global.get_type(), &name)
.get_address(None);
self.global_names.borrow_mut().insert(global, name.to_string());*/
return global;
}
let defined_in_current_codegen_unit =
self.codegen_unit.items().contains_key(&MonoItem::Static(def_id));
assert!(
!defined_in_current_codegen_unit,
"consts::get_static() should always hit the cache for \
statics defined in the same CGU, but did not for `{:?}`",
def_id
);
let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
let sym = self.tcx.symbol_name(instance).name;
//debug!("get_static: sym={} instance={:?}", sym, instance);
let global =
if let Some(def_id) = def_id.as_local() {
let id = self.tcx.hir().local_def_id_to_hir_id(def_id);
let llty = self.layout_of(ty).gcc_type(self, true);
// FIXME: refactor this to work without accessing the HIR
let global = match self.tcx.hir().get(id) {
Node::Item(&hir::Item { span, kind: hir::ItemKind::Static(..), .. }) => {
if let Some(global) = self.get_declared_value(&sym) {
if self.val_ty(global) != self.type_ptr_to(llty) {
span_bug!(span, "Conflicting types for static");
}
}
let is_tls = fn_attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL);
let global = self.declare_global(&sym, llty, is_tls, fn_attrs.link_section);
if !self.tcx.is_reachable_non_generic(def_id) {
/*unsafe {
llvm::LLVMRustSetVisibility(global, llvm::Visibility::Hidden);
}*/
}
global
}
Node::ForeignItem(&hir::ForeignItem {
span,
kind: hir::ForeignItemKind::Static(..),
..
}) => {
let fn_attrs = self.tcx.codegen_fn_attrs(def_id);
check_and_apply_linkage(&self, &fn_attrs, ty, sym, span)
}
item => bug!("get_static: expected static, found {:?}", item),
};
//debug!("get_static: sym={} attrs={:?}", sym, attrs);
global
}
else {
// FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
//debug!("get_static: sym={} item_attr={:?}", sym, self.tcx.item_attrs(def_id));
let attrs = self.tcx.codegen_fn_attrs(def_id);
let span = self.tcx.def_span(def_id);
let global = check_and_apply_linkage(&self, &attrs, ty, sym, span);
let needs_dll_storage_attr = false; /*self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
// ThinLTO can't handle this workaround in all cases, so we don't
// emit the attrs. Instead we make them unnecessary by disallowing
// dynamic linking when linker plugin based LTO is enabled.
!self.tcx.sess.opts.cg.linker_plugin_lto.enabled();*/
// If this assertion triggers, there's something wrong with commandline
// argument validation.
debug_assert!(
!(self.tcx.sess.opts.cg.linker_plugin_lto.enabled()
&& self.tcx.sess.target.options.is_like_msvc
&& self.tcx.sess.opts.cg.prefer_dynamic)
);
if needs_dll_storage_attr {
// This item is external but not foreign, i.e., it originates from an external Rust
// crate. Since we don't know whether this crate will be linked dynamically or
// statically in the final application, we always mark such symbols as 'dllimport'.
// If final linkage happens to be static, we rely on compiler-emitted __imp_ stubs
// to make things work.
//
// However, in some scenarios we defer emission of statics to downstream
// crates, so there are cases where a static with an upstream DefId
// is actually present in the current crate. We can find out via the
// is_codegened_item query.
if !self.tcx.is_codegened_item(def_id) {
unimplemented!();
/*unsafe {
llvm::LLVMSetDLLStorageClass(global, llvm::DLLStorageClass::DllImport);
}*/
}
}
global
};
/*if self.use_dll_storage_attrs && self.tcx.is_dllimport_foreign_item(def_id) {
// For foreign (native) libs we know the exact storage type to use.
unsafe {
llvm::LLVMSetDLLStorageClass(global, llvm::DLLStorageClass::DllImport);
}
}*/
self.instances.borrow_mut().insert(instance, global);
global
}
}
pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: &Allocation) -> RValue<'gcc> {
let mut llvals = Vec::with_capacity(alloc.relocations().len() + 1);
let dl = cx.data_layout();
let pointer_size = dl.pointer_size.bytes() as usize;
let mut next_offset = 0;
for &(offset, alloc_id) in alloc.relocations().iter() {
let offset = offset.bytes();
assert_eq!(offset as usize as u64, offset);
let offset = offset as usize;
if offset > next_offset {
// This `inspect` is okay since we have checked that it is not within a relocation, it
// is within the bounds of the allocation, and it doesn't affect interpreter execution
// (we inspect the result after interpreter execution). Any undef byte is replaced with
// some arbitrary byte value.
//
// FIXME: relay undef bytes to codegen as undef const bytes
let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(next_offset..offset);
llvals.push(cx.const_bytes(bytes));
}
let ptr_offset =
read_target_uint( dl.endian,
// This `inspect` is okay since it is within the bounds of the allocation, it doesn't
// affect interpreter execution (we inspect the result after interpreter execution),
// and we properly interpret the relocation as a relocation pointer offset.
alloc.inspect_with_uninit_and_ptr_outside_interpreter(offset..(offset + pointer_size)),
)
.expect("const_alloc_to_llvm: could not read relocation pointer")
as u64;
llvals.push(cx.scalar_to_backend(
InterpScalar::from_pointer(
interpret::Pointer::new(alloc_id, Size::from_bytes(ptr_offset)),
&cx.tcx,
),
&abi::Scalar { value: Primitive::Pointer, valid_range: 0..=!0 },
cx.type_i8p(),
));
next_offset = offset + pointer_size;
}
if alloc.len() >= next_offset {
let range = next_offset..alloc.len();
// This `inspect` is okay since we have check that it is after all relocations, it is
// within the bounds of the allocation, and it doesn't affect interpreter execution (we
// inspect the result after interpreter execution). Any undef byte is replaced with some
// arbitrary byte value.
//
// FIXME: relay undef bytes to codegen as undef const bytes
let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range);
llvals.push(cx.const_bytes(bytes));
}
cx.const_struct(&llvals, true)
}
pub fn codegen_static_initializer<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, def_id: DefId) -> Result<(RValue<'gcc>, &'tcx Allocation), ErrorHandled> {
let alloc = cx.tcx.eval_static_initializer(def_id)?;
Ok((const_alloc_to_gcc(cx, alloc), alloc))
}
fn check_and_apply_linkage<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, attrs: &CodegenFnAttrs, ty: Ty<'tcx>, sym: &str, span: Span) -> RValue<'gcc> {
let is_tls = attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL);
let llty = cx.layout_of(ty).gcc_type(cx, true);
if let Some(linkage) = attrs.linkage {
//debug!("get_static: sym={} linkage={:?}", sym, linkage);
// If this is a static with a linkage specified, then we need to handle
// it a little specially. The typesystem prevents things like &T and
// extern "C" fn() from being non-null, so we can't just declare a
// static and call it a day. Some linkages (like weak) will make it such
// that the static actually has a null value.
let llty2 =
if let ty::RawPtr(ref mt) = ty.kind() {
cx.layout_of(mt.ty).gcc_type(cx, true)
}
else {
cx.sess().span_fatal(
span,
"must have type `*const T` or `*mut T` due to `#[linkage]` attribute",
)
};
// Declare a symbol `foo` with the desired linkage.
let global1 = cx.declare_global_with_linkage(&sym, llty2, base::global_linkage_to_gcc(linkage));
// Declare an internal global `extern_with_linkage_foo` which
// is initialized with the address of `foo`. If `foo` is
// discarded during linking (for example, if `foo` has weak
// linkage and there are no definitions), then
// `extern_with_linkage_foo` will instead be initialized to
// zero.
let mut real_name = "_rust_extern_with_linkage_".to_string();
real_name.push_str(&sym);
let global2 =
cx.define_global(&real_name, llty, is_tls, attrs.link_section).unwrap_or_else(|| {
cx.sess().span_fatal(span, &format!("symbol `{}` is already defined", &sym))
});
//llvm::LLVMRustSetLinkage(global2, llvm::Linkage::InternalLinkage);
let lvalue = global2.dereference(None);
cx.global_init_block.add_assignment(None, lvalue, global1);
//llvm::LLVMSetInitializer(global2, global1);
global2
}
else {
// Generate an external declaration.
// FIXME(nagisa): investigate whether it can be changed into define_global
// Thread-local statics in some other crate need to *always* be linked
// against in a thread-local fashion, so we need to be sure to apply the
// thread-local attribute locally if it was present remotely. If we
// don't do this then linker errors can be generated where the linker
// complains that one object files has a thread local version of the
// symbol and another one doesn't.
cx.declare_global(&sym, llty, is_tls, attrs.link_section)
}
}