diff options
Diffstat (limited to 'compiler/rustc_codegen_gcc/src/consts.rs')
| -rw-r--r-- | compiler/rustc_codegen_gcc/src/consts.rs | 378 |
1 files changed, 378 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_gcc/src/consts.rs b/compiler/rustc_codegen_gcc/src/consts.rs new file mode 100644 index 00000000000..d8a1fd315c0 --- /dev/null +++ b/compiler/rustc_codegen_gcc/src/consts.rs @@ -0,0 +1,378 @@ +#[cfg(feature = "master")] +use gccjit::{FnAttribute, VarAttribute, Visibility}; +use gccjit::{Function, GlobalKind, LValue, RValue, ToRValue}; +use rustc_codegen_ssa::traits::{BaseTypeMethods, ConstMethods, DerivedTypeMethods, StaticMethods}; +use rustc_middle::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_middle::ty::layout::LayoutOf; +use rustc_middle::mir::interpret::{self, ConstAllocation, ErrorHandled, Scalar as InterpScalar, read_target_uint}; +use rustc_span::def_id::DefId; +use rustc_target::abi::{self, Align, HasDataLayout, Primitive, Size, WrappingRange}; + +use crate::base; +use crate::context::CodegenCx; +use crate::errors::InvalidMinimumAlignment; +use crate::type_of::LayoutGccExt; + +fn set_global_alignment<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, gv: LValue<'gcc>, mut align: Align) { + // The target may require greater alignment for globals than the type does. + // Note: GCC and Clang also allow `__attribute__((aligned))` on variables, + // which can force it to be smaller. Rust doesn't support this yet. + if let Some(min) = cx.sess().target.min_global_align { + match Align::from_bits(min) { + Ok(min) => align = align.max(min), + Err(err) => { + cx.sess().emit_err(InvalidMinimumAlignment { err: err.to_string() }); + } + } + } + gv.set_alignment(align.bytes() as i32); +} + +impl<'gcc, 'tcx> StaticMethods for CodegenCx<'gcc, 'tcx> { + fn static_addr_of(&self, cv: RValue<'gcc>, align: Align, kind: Option<&str>) -> RValue<'gcc> { + // TODO(antoyo): implement a proper rvalue comparison in libgccjit instead of doing the + // following: + for (value, variable) in &*self.const_globals.borrow() { + if format!("{:?}", value) == format!("{:?}", cv) { + if let Some(global_variable) = self.global_lvalues.borrow().get(variable) { + let alignment = align.bits() as i32; + if alignment > global_variable.get_alignment() { + global_variable.set_alignment(alignment); + } + } + return *variable; + } + } + let global_value = self.static_addr_of_mut(cv, align, kind); + #[cfg(feature = "master")] + self.global_lvalues.borrow().get(&global_value) + .expect("`static_addr_of_mut` did not add the global to `self.global_lvalues`") + .global_set_readonly(); + 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 value = + match codegen_static_initializer(&self, def_id) { + Ok((value, _)) => value, + // Error has already been reported + Err(_) => return, + }; + + 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() { + unimplemented!(); + } + 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); + + set_global_alignment(self, global, self.align_of(ty)); + + let value = self.bitcast_if_needed(value, gcc_type); + global.global_set_initializer_rvalue(value); + + // 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) { + #[cfg(feature = "master")] + global.global_set_readonly(); + } + } + + 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 for provenance, 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. + unimplemented!(); + } + } + + // 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!(); + } + } else { + // TODO(antoyo): set link section. + } + + if attrs.flags.contains(CodegenFnAttrFlags::USED) || attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) { + self.add_used_global(global.to_rvalue()); + } + } + + /// 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(antoyo) + } + + fn add_compiler_used_global(&self, global: RValue<'gcc>) { + // NOTE: seems like GCC does not make the distinction between compiler.used and used. + self.add_used_global(global); + } +} + +impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> { + #[cfg_attr(not(feature="master"), allow(unused_variables))] + pub fn add_used_function(&self, function: Function<'gcc>) { + #[cfg(feature = "master")] + function.add_attribute(FnAttribute::Used); + } + + pub fn static_addr_of_mut(&self, cv: RValue<'gcc>, align: Align, kind: Option<&str>) -> RValue<'gcc> { + let global = + match kind { + Some(kind) if !self.tcx.sess.fewer_names() => { + let name = self.generate_local_symbol_name(kind); + // TODO(antoyo): check if it's okay that no link_section is set. + + let typ = self.val_ty(cv).get_aligned(align.bytes()); + let global = self.declare_private_global(&name[..], typ); + global + } + _ => { + let typ = self.val_ty(cv).get_aligned(align.bytes()); + let global = self.declare_unnamed_global(typ); + global + }, + }; + global.global_set_initializer_rvalue(cv); + // TODO(antoyo): set unnamed address. + let rvalue = global.get_address(None); + self.global_lvalues.borrow_mut().insert(rvalue, global); + rvalue + } + + pub fn get_static(&self, def_id: DefId) -> LValue<'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) { + 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; + + let global = + if def_id.is_local() && !self.tcx.is_foreign_item(def_id) { + let llty = self.layout_of(ty).gcc_type(self); + if let Some(global) = self.get_declared_value(sym) { + if self.val_ty(global) != self.type_ptr_to(llty) { + span_bug!(self.tcx.def_span(def_id), "Conflicting types for static"); + } + } + + let is_tls = fn_attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL); + let global = self.declare_global( + &sym, + llty, + GlobalKind::Exported, + is_tls, + fn_attrs.link_section, + ); + + if !self.tcx.is_reachable_non_generic(def_id) { + #[cfg(feature = "master")] + global.add_attribute(VarAttribute::Visibility(Visibility::Hidden)); + } + + global + } else { + check_and_apply_linkage(&self, &fn_attrs, ty, sym) + }; + + if !def_id.is_local() { + let needs_dll_storage_attr = false; // TODO(antoyo) + + // 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!(); + } + } + } + + // TODO(antoyo): set dll storage class. + + self.instances.borrow_mut().insert(instance, global); + global + } +} + +pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: ConstAllocation<'tcx>) -> RValue<'gcc> { + let alloc = alloc.inner(); + let mut llvals = Vec::with_capacity(alloc.provenance().ptrs().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.provenance().ptrs().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 pointer with provenance, 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 provenance 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; + + let address_space = cx.tcx.global_alloc(alloc_id).address_space(cx); + + llvals.push(cx.scalar_to_backend( + InterpScalar::from_pointer( + interpret::Pointer::new(alloc_id, Size::from_bytes(ptr_offset)), + &cx.tcx, + ), + abi::Scalar::Initialized { value: Primitive::Pointer(address_space), valid_range: WrappingRange::full(dl.pointer_size) }, + cx.type_i8p_ext(address_space), + )); + 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 provenance, 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>, ConstAllocation<'tcx>), 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) -> LValue<'gcc> { + let is_tls = attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL); + let gcc_type = cx.layout_of(ty).gcc_type(cx); + if let Some(linkage) = attrs.import_linkage { + // Declare a symbol `foo` with the desired linkage. + let global1 = cx.declare_global_with_linkage(&sym, cx.type_i8(), 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, gcc_type, is_tls, attrs.link_section); + // TODO(antoyo): set linkage. + let value = cx.const_ptrcast(global1.get_address(None), gcc_type); + global2.global_set_initializer_rvalue(value); + // TODO(antoyo): use global_set_initializer() when it will work. + 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, gcc_type, GlobalKind::Imported, is_tls, attrs.link_section) + } +} |