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[IR] Make stack protector symbol dso_local according to -f[no-]direct-access-external-data
There are two motivations. `-fno-pic -fstack-protector -mstack-protector-guard=global` created `__stack_chk_guard` is referenced directly on all ELF OSes except FreeBSD. This patch allows referencing the symbol indirectly with -fno-direct-access-external-data. Some Linux kernel folks want `-fno-pic -fstack-protector -mstack-protector-guard-reg=gs -mstack-protector-guard-symbol=__stack_chk_guard` created `__stack_chk_guard` to be referenced directly, avoiding R_X86_64_REX_GOTPCRELX (even if the relocation may be optimized out by the linker). #60116 Why they need this isn't so clear to me. --- Add module flag "direct-access-external-data" and set the dso_local property of the stack protector symbol. The module flag can benefit other LLVMCodeGen synthesized symbols that are not represented in LLVM IR. Nowadays, with `-fno-pic` being uncommon, ideally we should set "direct-access-external-data" when it is true. However, doing so would require ~90 clang/test tests to be updated, which are too much. As a compromise, we set "direct-access-external-data" only when it's different from the implied default value. Reviewed By: nickdesaulniers Differential Revision: https://reviews.llvm.org/D150841
1 parent 7140050 commit e018cbf

20 files changed

+109
-17
lines changed

‎clang/lib/CodeGen/CodeGenModule.cpp‎

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@@ -908,6 +908,12 @@ void CodeGenModule::Release() {
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if (CodeGenOpts.NoPLT)
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getModule().setRtLibUseGOT();
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if (getTriple().isOSBinFormatELF() &&
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CodeGenOpts.DirectAccessExternalData !=
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getModule().getDirectAccessExternalData()) {
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getModule().setDirectAccessExternalData(
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CodeGenOpts.DirectAccessExternalData);
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}
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if (CodeGenOpts.UnwindTables)
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getModule().setUwtable(llvm::UWTableKind(CodeGenOpts.UnwindTables));
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‎clang/test/CodeGen/dso-local-executable.c‎

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@@ -36,6 +36,8 @@
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// STATIC-DAG: define dso_local ptr @zed()
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// STATIC-DAG: declare dso_local void @import_func()
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// STATIC-NOT: !"direct-access-external-data"
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/// If -fno-direct-access-external-data is set, drop dso_local from global variable
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/// declarations.
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// RUN: %clang_cc1 -triple x86_64 -emit-llvm %s -mrelocation-model static -fno-direct-access-external-data -o - | FileCheck --check-prefix=STATIC-INDIRECT %s
@@ -49,6 +51,8 @@
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// STATIC-INDIRECT-DAG: define dso_local ptr @zed()
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// STATIC-INDIRECT-DAG: declare void @foo()
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// STATIC-INDIRECT: ![[#]] = !{i32 7, !"direct-access-external-data", i32 0}
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// RUN: %clang_cc1 -triple x86_64 -emit-llvm -pic-level 1 -pic-is-pie %s -o - | FileCheck --check-prefix=PIE %s
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// PIE: @baz = dso_local global i32 42
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// PIE-NEXT: @import_var = external global i32
@@ -60,6 +64,8 @@
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// PIE-DAG: define dso_local ptr @zed()
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// PIE-DAG: declare void @import_func()
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// PIE-NOT: !"direct-access-external-data"
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// RUN: %clang_cc1 -triple x86_64 -emit-llvm -pic-level 1 -pic-is-pie -fdirect-access-external-data %s -o - | FileCheck --check-prefix=PIE-DIRECT %s
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// PIE-DIRECT: @baz = dso_local global i32 42
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// PIE-DIRECT-NEXT: @import_var = external dso_local global i32
@@ -71,6 +77,8 @@
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// PIE-DIRECT-DAG: define dso_local ptr @zed()
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// PIE-DIRECT-DAG: declare void @import_func()
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// PIE-DIRECT: ![[#]] = !{i32 7, !"direct-access-external-data", i32 1}
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// RUN: %clang_cc1 -triple x86_64 -emit-llvm -mrelocation-model static -fno-plt %s -o - | FileCheck --check-prefix=NOPLT %s
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// NOPLT: @baz = dso_local global i32 42
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// NOPLT-NEXT: @import_var = external dso_local global i32

‎llvm/include/llvm/IR/Module.h‎

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@@ -945,6 +945,11 @@ class LLVM_EXTERNAL_VISIBILITY Module {
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/// Set that PLT should be avoid for RTLib calls.
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void setRtLibUseGOT();
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/// Get/set whether referencing global variables can use direct access
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/// relocations on ELF targets.
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bool getDirectAccessExternalData() const;
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void setDirectAccessExternalData(bool Value);
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/// Get/set whether synthesized functions should get the uwtable attribute.
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UWTableKind getUwtable() const;
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void setUwtable(UWTableKind Kind);

‎llvm/lib/CodeGen/TargetLoweringBase.cpp‎

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@@ -1977,7 +1977,7 @@ void TargetLoweringBase::insertSSPDeclarations(Module &M) const {
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"__stack_chk_guard");
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// FreeBSD has "__stack_chk_guard" defined externally on libc.so
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if (TM.getRelocationModel() == Reloc::Static &&
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if (M.getDirectAccessExternalData() &&
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!TM.getTargetTriple().isWindowsGNUEnvironment() &&
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!TM.getTargetTriple().isOSFreeBSD())
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GV->setDSOLocal(true);

‎llvm/lib/IR/Module.cpp‎

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@@ -672,6 +672,18 @@ void Module::setRtLibUseGOT() {
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addModuleFlag(ModFlagBehavior::Max, "RtLibUseGOT", 1);
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}
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bool Module::getDirectAccessExternalData() const {
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auto *Val = cast_or_null<ConstantAsMetadata>(
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getModuleFlag("direct-access-external-data"));
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if (Val)
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return cast<ConstantInt>(Val->getValue())->getZExtValue() > 0;
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return getPICLevel() == PICLevel::NotPIC;
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}
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void Module::setDirectAccessExternalData(bool Value) {
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addModuleFlag(ModFlagBehavior::Max, "direct-access-external-data", Value);
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}
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UWTableKind Module::getUwtable() const {
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if (auto *Val = cast_or_null<ConstantAsMetadata>(getModuleFlag("uwtable")))
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return UWTableKind(cast<ConstantInt>(Val->getValue())->getZExtValue());

‎llvm/lib/Target/X86/X86ISelLowering.cpp‎

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@@ -3074,6 +3074,7 @@ Value *X86TargetLowering::getIRStackGuard(IRBuilderBase &IRB) const {
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GV = new GlobalVariable(*M, Ty, false, GlobalValue::ExternalLinkage,
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nullptr, GuardSymb, nullptr,
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GlobalValue::NotThreadLocal, AddressSpace);
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GV->setDSOLocal(M->getDirectAccessExternalData());
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}
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return GV;
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}

‎llvm/test/CodeGen/AArch64/arm64_32.ll‎

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@@ -759,3 +759,6 @@ define void @test_bzero(i64 %in) {
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}
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declare void @llvm.memset.p0.i32(ptr nocapture writeonly, i8, i32, i1)
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!llvm.module.flags = !{!0}
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!0 = !{i32 7, !"PIC Level", i32 2}

‎llvm/test/CodeGen/AArch64/stack-guard-sve.ll‎

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@@ -337,3 +337,6 @@ entry:
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attributes #0 = { ssp "frame-pointer"="non-leaf" }
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attributes #1 = { sspstrong "frame-pointer"="non-leaf" }
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!llvm.module.flags = !{!0}
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!0 = !{i32 7, !"direct-access-external-data", i32 1}

‎llvm/test/CodeGen/AArch64/stack-guard-vaarg.ll‎

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@@ -36,3 +36,6 @@ declare void @llvm.va_end(ptr)
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declare void @llvm.lifetime.end(i64, ptr nocapture)
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attributes #0 = { noinline nounwind optnone ssp }
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!llvm.module.flags = !{!0}
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!0 = !{i32 7, !"direct-access-external-data", i32 1}

‎llvm/test/CodeGen/AArch64/stack_guard_remat.ll‎

Lines changed: 18 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,16 @@
1-
; RUN: llc < %s -mtriple=arm64-apple-ios -relocation-model=pic -no-integrated-as | FileCheck %s -check-prefix=DARWIN
2-
; RUN: llc < %s -mtriple=arm64-apple-ios -relocation-model=static -no-integrated-as | FileCheck %s -check-prefix=DARWIN
3-
; RUN: llc < %s -mtriple=aarch64-linux-gnu -relocation-model=pic -no-integrated-as | FileCheck %s -check-prefix=PIC-LINUX
4-
; RUN: llc < %s -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=large -no-integrated-as | FileCheck %s -check-prefix=STATIC-LARGE
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; RUN: llc < %s -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=small -no-integrated-as | FileCheck %s -check-prefix=STATIC-SMALL
6-
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; RUN: llc < %s -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=arm64-apple-ios -relocation-model=pic -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=DARWIN,FALLBACK
8-
; RUN: llc < %s -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=arm64-apple-ios -relocation-model=static -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=DARWIN,FALLBACK
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; RUN: llc < %s -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=aarch64-linux-gnu -relocation-model=pic -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=PIC-LINUX,FALLBACK
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; RUN: llc < %s -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=large -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=STATIC-LARGE,FALLBACK
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; RUN: llc < %s -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=small -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=STATIC-SMALL,FALLBACK
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; RUN: rm -rf %t && split-file %s %t && cd %t
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; RUN: cat a.ll pic.ll > b.ll
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; RUN: llc < b.ll -mtriple=arm64-apple-ios -relocation-model=pic -no-integrated-as | FileCheck %s -check-prefix=DARWIN
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; RUN: llc < b.ll -mtriple=arm64-apple-ios -relocation-model=static -no-integrated-as | FileCheck %s -check-prefix=DARWIN
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; RUN: llc < b.ll -mtriple=aarch64-linux-gnu -relocation-model=pic -no-integrated-as | FileCheck %s -check-prefix=PIC-LINUX
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; RUN: llc < a.ll -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=large -no-integrated-as | FileCheck %s -check-prefix=STATIC-LARGE
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; RUN: llc < a.ll -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=small -no-integrated-as | FileCheck %s -check-prefix=STATIC-SMALL
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; RUN: llc < b.ll -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=arm64-apple-ios -relocation-model=pic -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=DARWIN,FALLBACK
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; RUN: llc < b.ll -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=arm64-apple-ios -relocation-model=static -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=DARWIN,FALLBACK
11+
; RUN: llc < b.ll -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=aarch64-linux-gnu -relocation-model=pic -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=PIC-LINUX,FALLBACK
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; RUN: llc < a.ll -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=large -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=STATIC-LARGE,FALLBACK
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; RUN: llc < a.ll -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel* -mtriple=aarch64-linux-gnu -relocation-model=static -code-model=small -no-integrated-as 2>&1 | FileCheck %s -check-prefixes=STATIC-SMALL,FALLBACK
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1315
; DARWIN: foo2
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; DARWIN: adrp [[R0:x[0-9]+]], ___stack_chk_guard@GOTPAGE
@@ -33,6 +35,7 @@
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; FALLBACK-NOT: remark:{{.*}}llvm.lifetime.end
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; FALLBACK-NOT: remark:{{.*}}llvm.lifetime.start
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;--- a.ll
3639
define i32 @test_stack_guard_remat() #0 {
3740
entry:
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%a1 = alloca [256 x i32], align 4
@@ -52,3 +55,7 @@ declare void @foo3(ptr)
5255
declare void @llvm.lifetime.end.p0(i64, ptr nocapture)
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attributes #0 = { nounwind sspstrong "less-precise-fpmad"="false" "frame-pointer"="all" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
58+
59+
;--- pic.ll
60+
!llvm.module.flags = !{!0}
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!0 = !{i32 8, !"PIC Level", i32 2}

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