From 06a41687b160cbb4cbf8fce0b3ad3a2e352e8338 Mon Sep 17 00:00:00 2001 From: WANG Rui Date: Thu, 14 Dec 2023 22:07:53 +0800 Subject: [PATCH] Add unstable `-Z direct-access-external-data` cmdline flag for `rustc` The new flag has been described in the Major Change Proposal at https://github.com/rust-lang/compiler-team/issues/707 --- compiler/rustc_codegen_llvm/src/mono_item.rs | 25 +++++++++++-------- compiler/rustc_interface/src/tests.rs | 1 + compiler/rustc_session/src/options.rs | 2 ++ compiler/rustc_session/src/session.rs | 7 ++++++ compiler/rustc_target/src/spec/mod.rs | 11 ++++++++ .../targets/loongarch64_unknown_linux_gnu.rs | 1 + .../direct-access-external-data.md | 16 ++++++++++++ tests/codegen/direct-access-external-data.rs | 21 ++++++++++++++++ 8 files changed, 74 insertions(+), 10 deletions(-) create mode 100644 src/doc/unstable-book/src/compiler-flags/direct-access-external-data.md create mode 100644 tests/codegen/direct-access-external-data.rs diff --git a/compiler/rustc_codegen_llvm/src/mono_item.rs b/compiler/rustc_codegen_llvm/src/mono_item.rs index f796ce0990f..f7630719368 100644 --- a/compiler/rustc_codegen_llvm/src/mono_item.rs +++ b/compiler/rustc_codegen_llvm/src/mono_item.rs @@ -123,6 +123,17 @@ impl CodegenCx<'_, '_> { return false; } + // Match clang by only supporting COFF and ELF for now. + if self.tcx.sess.target.is_like_osx { + return false; + } + + // With pie relocation model calls of functions defined in the translation + // unit can use copy relocations. + if self.tcx.sess.relocation_model() == RelocModel::Pie && !is_declaration { + return true; + } + // Thread-local variables generally don't support copy relocations. let is_thread_local_var = llvm::LLVMIsAGlobalVariable(llval) .is_some_and(|v| llvm::LLVMIsThreadLocal(v) == llvm::True); @@ -130,18 +141,12 @@ impl CodegenCx<'_, '_> { return false; } - // Match clang by only supporting COFF and ELF for now. - if self.tcx.sess.target.is_like_osx { - return false; + // Respect the direct-access-external-data to override default behavior if present. + if let Some(direct) = self.tcx.sess.direct_access_external_data() { + return direct; } // Static relocation model should force copy relocations everywhere. - if self.tcx.sess.relocation_model() == RelocModel::Static { - return true; - } - - // With pie relocation model calls of functions defined in the translation - // unit can use copy relocations. - self.tcx.sess.relocation_model() == RelocModel::Pie && !is_declaration + self.tcx.sess.relocation_model() == RelocModel::Static } } diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs index 588139a303c..948db6a6ea1 100644 --- a/compiler/rustc_interface/src/tests.rs +++ b/compiler/rustc_interface/src/tests.rs @@ -748,6 +748,7 @@ fn test_unstable_options_tracking_hash() { tracked!(debug_macros, true); tracked!(default_hidden_visibility, Some(true)); tracked!(dep_info_omit_d_target, true); + tracked!(direct_access_external_data, Some(true)); tracked!(dual_proc_macros, true); tracked!(dwarf_version, Some(5)); tracked!(emit_thin_lto, false); diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs index c97b18ebd66..ff8c5f4b356 100644 --- a/compiler/rustc_session/src/options.rs +++ b/compiler/rustc_session/src/options.rs @@ -1553,6 +1553,8 @@ options! { dep_info_omit_d_target: bool = (false, parse_bool, [TRACKED], "in dep-info output, omit targets for tracking dependencies of the dep-info files \ themselves (default: no)"), + direct_access_external_data: Option = (None, parse_opt_bool, [TRACKED], + "Direct or use GOT indirect to reference external data symbols"), dual_proc_macros: bool = (false, parse_bool, [TRACKED], "load proc macros for both target and host, but only link to the target (default: no)"), dump_dep_graph: bool = (false, parse_bool, [UNTRACKED], diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs index 720599f6095..392485e2238 100644 --- a/compiler/rustc_session/src/session.rs +++ b/compiler/rustc_session/src/session.rs @@ -793,6 +793,13 @@ impl Session { self.opts.unstable_opts.tls_model.unwrap_or(self.target.tls_model) } + pub fn direct_access_external_data(&self) -> Option { + self.opts + .unstable_opts + .direct_access_external_data + .or(self.target.direct_access_external_data) + } + pub fn split_debuginfo(&self) -> SplitDebuginfo { self.opts.cg.split_debuginfo.unwrap_or(self.target.split_debuginfo) } diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs index 8e26327196a..7979be7b5d6 100644 --- a/compiler/rustc_target/src/spec/mod.rs +++ b/compiler/rustc_target/src/spec/mod.rs @@ -1885,6 +1885,8 @@ pub struct TargetOptions { /// passed, and cannot be disabled even via `-C`. Corresponds to `llc /// -mattr=$features`. pub features: StaticCow, + /// Direct or use GOT indirect to reference external data symbols + pub direct_access_external_data: Option, /// Whether dynamic linking is available on this target. Defaults to false. pub dynamic_linking: bool, /// Whether dynamic linking can export TLS globals. Defaults to true. @@ -2279,6 +2281,7 @@ impl Default for TargetOptions { asm_args: cvs![], cpu: "generic".into(), features: "".into(), + direct_access_external_data: None, dynamic_linking: false, dll_tls_export: true, only_cdylib: false, @@ -2575,6 +2578,12 @@ impl Target { base.$key_name = s as u32; } } ); + ($key_name:ident, Option) => ( { + let name = (stringify!($key_name)).replace("_", "-"); + if let Some(s) = obj.remove(&name).and_then(|b| b.as_bool()) { + base.$key_name = Some(s); + } + } ); ($key_name:ident, Option) => ( { let name = (stringify!($key_name)).replace("_", "-"); if let Some(s) = obj.remove(&name).and_then(|b| b.as_u64()) { @@ -3003,6 +3012,7 @@ impl Target { key!(cpu); key!(features); key!(dynamic_linking, bool); + key!(direct_access_external_data, Option); key!(dll_tls_export, bool); key!(only_cdylib, bool); key!(executables, bool); @@ -3257,6 +3267,7 @@ impl ToJson for Target { target_option_val!(cpu); target_option_val!(features); target_option_val!(dynamic_linking); + target_option_val!(direct_access_external_data); target_option_val!(dll_tls_export); target_option_val!(only_cdylib); target_option_val!(executables); diff --git a/compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_gnu.rs b/compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_gnu.rs index 0f05e7c475a..234270c999b 100644 --- a/compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_gnu.rs +++ b/compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_gnu.rs @@ -11,6 +11,7 @@ pub fn target() -> Target { features: "+f,+d".into(), llvm_abiname: "lp64d".into(), max_atomic_width: Some(64), + direct_access_external_data: Some(false), ..base::linux_gnu::opts() }, } diff --git a/src/doc/unstable-book/src/compiler-flags/direct-access-external-data.md b/src/doc/unstable-book/src/compiler-flags/direct-access-external-data.md new file mode 100644 index 00000000000..c72df437960 --- /dev/null +++ b/src/doc/unstable-book/src/compiler-flags/direct-access-external-data.md @@ -0,0 +1,16 @@ +# `direct_access_external_data` + +The tracking issue for this feature is: https://github.com/rust-lang/compiler-team/issues/707 + +------------------------ + +Option `-Z direct-access-external-data` controls how to access symbols of +external data. + +Supported values for this option are: + +- `yes` - Don't use GOT indirection to reference external data symbols. +- `no` - Use GOT indirection to reference external data symbols. + +If the option is not explicitly specified, different targets have different +default values. diff --git a/tests/codegen/direct-access-external-data.rs b/tests/codegen/direct-access-external-data.rs new file mode 100644 index 00000000000..ec4bfc33518 --- /dev/null +++ b/tests/codegen/direct-access-external-data.rs @@ -0,0 +1,21 @@ +// only-loongarch64-unknown-linux-gnu + +// revisions: DEFAULT DIRECT INDIRECT +// [DEFAULT] compile-flags: -C relocation-model=static +// [DIRECT] compile-flags: -C relocation-model=static -Z direct-access-external-data=yes +// [INDIRECT] compile-flags: -C relocation-model=static -Z direct-access-external-data=no + +#![crate_type = "rlib"] + +// DEFAULT: @VAR = external {{.*}} global i32 +// DIRECT: @VAR = external dso_local {{.*}} global i32 +// INDIRECT: @VAR = external {{.*}} global i32 + +extern "C" { + static VAR: i32; +} + +#[no_mangle] +pub fn get() -> i32 { + unsafe { VAR } +}