[lld] [llvm] [lld] Discard SHT_LLVM_LTO sections in relocatable links (PR #92825)
Paul Kirth via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 5 13:00:44 PDT 2024
https://github.com/ilovepi updated https://github.com/llvm/llvm-project/pull/92825
>From d4228eb0774a94536c1b47ee4e331586f23b2a8a Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Mon, 20 May 2024 14:45:11 -0700
Subject: [PATCH 1/2] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20ch?=
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Created using spr 1.3.4
[skip ci]
---
lld/test/ELF/fatlto/fatlto.test | 41 +++++++++++++++++++
.../CodeGen/TargetLoweringObjectFileImpl.cpp | 3 ++
llvm/test/CodeGen/X86/fat-lto-section.ll | 2 +-
3 files changed, 45 insertions(+), 1 deletion(-)
diff --git a/lld/test/ELF/fatlto/fatlto.test b/lld/test/ELF/fatlto/fatlto.test
index edf4ef2da2b88..e250325dc54f4 100644
--- a/lld/test/ELF/fatlto/fatlto.test
+++ b/lld/test/ELF/fatlto/fatlto.test
@@ -49,6 +49,25 @@
; RUN: ld.lld -o %t/foo-fatLTO.archive %t/a.a %t/main-LTO.bc --fat-lto-objects
; RUN: cmp %t/foo-fatLTO.archive %t/foo-LTO
+;; Test FatLTO works with relocatable links using PIC objects
+;; Currently, with PIC relocatable links, FatLTO sections are treated as
+;; orphan sections and incorrectly concatenated together. This test verifies
+;; the current behavior, but should be fixed to either merge those sections
+;; correctly, or to drop them altogether.
+; RUN: opt < %t/a-LTO.ll -passes="embed-bitcode<thinlto;emit-summary>" | llc --relocation-model=pic --filetype=obj -o %t/a-fat-pic.o
+; RUN: llvm-readobj -S %t/a-fat-pic.o | FileCheck --check-prefix=HAS_LLVM_LTO %s
+
+; RUN: opt < %t/b-LTO.ll -passes="embed-bitcode<thinlto;emit-summary>" | llc --relocation-model=pic --filetype=obj -o %t/b-fat-pic.o
+; RUN: llvm-readobj -S %t/b-fat-pic.o | FileCheck --check-prefix=HAS_LLVM_LTO %s
+
+; RUN: llvm-ar rcs %t/fat.pic.archive %t/a-fat-pic.o %t/b-fat-pic.o
+; RUN: llvm-readobj -S %t/fat.pic.archive | FileCheck --check-prefix=HAS_LLVM_LTO %s
+
+; RUN: ld.lld --whole-archive %t/fat.pic.archive -r -o %t/fat-pic-relocatable.o
+; RUN: llvm-readobj -S %t/fat-pic-relocatable.o | FileCheck --check-prefix=HAS_LLVM_LTO %s
+
+; HAS_LLVM_LTO: Name: .llvm.lto
+
;--- a-LTO.ll
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"
@@ -71,6 +90,28 @@ attributes #0 = { noinline nounwind uwtable }
!5 = !{i32 1, !"ThinLTO", i32 0}
!6 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+;--- b-LTO.ll
+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"
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i32 @foo() #0 {
+entry:
+ ret i32 0
+}
+
+attributes #0 = { noinline nounwind uwtable }
+
+!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"PIC Level", i32 2}
+!2 = !{i32 7, !"PIE Level", i32 2}
+!3 = !{i32 7, !"uwtable", i32 2}
+!4 = !{i32 7, !"frame-pointer", i32 2}
+!5 = !{i32 1, !"ThinLTO", i32 0}
+!6 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+
;--- main-LTO.ll
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"
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 3e1897ce670a6..567e9443759f1 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -527,6 +527,9 @@ static unsigned getELFSectionType(StringRef Name, SectionKind K) {
if (K.isBSS() || K.isThreadBSS())
return ELF::SHT_NOBITS;
+ if(hasPrefix(Name, ".llvm.lto"))
+ return ELF::SHT_LLVM_LTO;
+
return ELF::SHT_PROGBITS;
}
diff --git a/llvm/test/CodeGen/X86/fat-lto-section.ll b/llvm/test/CodeGen/X86/fat-lto-section.ll
index 30c56229a0e2a..f3ca8436affb4 100644
--- a/llvm/test/CodeGen/X86/fat-lto-section.ll
+++ b/llvm/test/CodeGen/X86/fat-lto-section.ll
@@ -5,6 +5,6 @@
; RUN: | FileCheck %s --check-prefix=EXCLUDE
; EXCLUDE: Name Type {{.*}} ES Flg Lk Inf Al
-; EXCLUDE: .llvm.lto PROGBITS {{.*}} 00 E 0 0 1
+; EXCLUDE: .llvm.lto LLVM_LTO {{.*}} 00 E 0 0 1
@a = global i32 1
>From 0b9155faf2dc063f81091c8e78d14dd4446c2db5 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Tue, 21 May 2024 09:58:46 -0700
Subject: [PATCH 2/2] Fix fallthrough and update comment
Created using spr 1.3.4
---
lld/ELF/InputFiles.cpp | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index 0ac49761601c4..33fd86b269f81 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -833,14 +833,15 @@ void ObjFile<ELFT>::initializeSections(bool ignoreComdats,
createInputSection(i, sec, check(obj.getSectionName(sec, shstrtab)));
break;
case SHT_LLVM_LTO:
- // When doing a relocatable link with FatLTO objects, if we're not using
- // the bitcode, discard it, since it will be concatenated together when
- // handling orphan sections, and which will be an invalid bitcode object.
+ // Discard .llvm.lto in a relocatable link that does not use the bitcode.
+ // The concatenated output does not properly reflect the linking
+ // semantics. In addition, since we do not use the bitcode wrapper format,
+ // the concatenated raw bitcode would be invalid.
if (config->relocatable && !config->fatLTOObjects) {
sections[i] = &InputSection::discarded;
break;
}
- LLVM_FALLTHROUGH;
+ [[fallthrough]];
default:
this->sections[i] =
createInputSection(i, sec, check(obj.getSectionName(sec, shstrtab)));
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