be8450eec8
Set dso_local for more items Related to https://github.com/rust-lang/rust/pull/83592. (cc `@nagisa)` Noticed that on x86_64 with `relocation-model: static` `R_X86_64_GOTPCREL` relocations were still generated in some cases. (related: https://github.com/Rust-for-Linux/linux/issues/135; Rust-for-Linux needs these fixes to successfully build) First time doing anything with LLVM so not sure whether this is correct but the following are some of the things I've tried to convince myself. ## C equivalent Example from clang which also sets `dso_local` in these cases: `clang-12 -fno-PIC -S -emit-llvm test.c` ```C extern int A; int* a() { return &A; } int B; int* b() { return &B; } ``` ``` ; ModuleID = 'test.c' source_filename = "test.c" target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" target triple = "x86_64-unknown-linux-gnu" `@A` = external dso_local global i32, align 4 `@B` = dso_local global i32 0, align 4 ; Function Attrs: noinline nounwind optnone uwtable define dso_local i32* `@a()` #0 { ret i32* `@A` } ; Function Attrs: noinline nounwind optnone uwtable define dso_local i32* `@b()` #0 { ret i32* `@B` } attributes #0 = { noinline nounwind optnone uwtable "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" } !llvm.module.flags = !{!0} !llvm.ident = !{!1} !0 = !{i32 1, !"wchar_size", i32 4} !1 = !{!"clang version 12.0.0 (https://github.com/llvm/llvm-project/ b978a93635b584db380274d7c8963c73989944a1)"} ``` `clang-12 -fno-PIC -c test.c` `objdump test.o -r`: ``` test.o: file format elf64-x86-64 RELOCATION RECORDS FOR [.text]: OFFSET TYPE VALUE 0000000000000006 R_X86_64_64 A 0000000000000016 R_X86_64_64 B RELOCATION RECORDS FOR [.eh_frame]: OFFSET TYPE VALUE 0000000000000020 R_X86_64_PC32 .text 0000000000000040 R_X86_64_PC32 .text+0x0000000000000010 ``` ## Comparison to pre-LLVM 12 output `rustc --emit=obj,llvm-ir --target=x86_64-unknown-none-linuxkernel --crate-type rlib test.rs` ```Rust #![feature(no_core, lang_items)] #![no_core] #[lang="sized"] trait Sized {} #[lang="sync"] trait Sync {} #[lang = "drop_in_place"] pub unsafe fn drop_in_place<T: ?Sized>(_: *mut T) {} impl Sync for i32 {} pub static STATIC: i32 = 32; extern { pub static EXT_STATIC: i32; } pub fn a() -> &'static i32 { &STATIC } pub fn b() -> &'static i32 { unsafe {&EXT_STATIC} } ``` `objdump test.o -r` nightly-2021-02-20 (rustc target is `x86_64-linux-kernel`): ``` RELOCATION RECORDS FOR [.text._ZN4test1a17h1024ba65f3424175E]: OFFSET TYPE VALUE 0000000000000007 R_X86_64_32S _ZN4test6STATIC17h3adc41a83746c9ffE RELOCATION RECORDS FOR [.text._ZN4test1b17h86a6a80c1190ac8dE]: OFFSET TYPE VALUE 0000000000000007 R_X86_64_32S EXT_STATIC ``` nightly-2021-05-10: ``` RELOCATION RECORDS FOR [.text._ZN4test1a17he846f03bf37b2d20E]: OFFSET TYPE VALUE 0000000000000007 R_X86_64_GOTPCREL _ZN4test6STATIC17h5a059515bf3d4968E-0x0000000000000004 RELOCATION RECORDS FOR [.text._ZN4test1b17h7e0f7f80fbd91125E]: OFFSET TYPE VALUE 0000000000000007 R_X86_64_GOTPCREL EXT_STATIC-0x0000000000000004 ``` This PR: ``` RELOCATION RECORDS FOR [.text._ZN4test1a17he846f03bf37b2d20E]: OFFSET TYPE VALUE 0000000000000007 R_X86_64_32S _ZN4test6STATIC17h5a059515bf3d4968E RELOCATION RECORDS FOR [.text._ZN4test1b17h7e0f7f80fbd91125E]: OFFSET TYPE VALUE 0000000000000007 R_X86_64_32S EXT_STATIC ``` |
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| .. | ||
| src | ||
| Cargo.toml | ||
| README.md | ||
The codegen crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.