r360984 - [ELF] Implement Dependent Libraries Feature
Ben Dunbobbin via cfe-commits
cfe-commits at lists.llvm.org
Thu May 16 20:44:16 PDT 2019
Author: bd1976llvm
Date: Thu May 16 20:44:15 2019
New Revision: 360984
URL: http://llvm.org/viewvc/llvm-project?rev=360984&view=rev
Log:
[ELF] Implement Dependent Libraries Feature
This patch implements a limited form of autolinking primarily designed to allow
either the --dependent-library compiler option, or "comment lib" pragmas (
https://docs.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=vs-2017) in
C/C++ e.g. #pragma comment(lib, "foo"), to cause an ELF linker to automatically
add the specified library to the link when processing the input file generated
by the compiler.
Currently this extension is unique to LLVM and LLD. However, care has been taken
to design this feature so that it could be supported by other ELF linkers.
The design goals were to provide:
- A simple linking model for developers to reason about.
- The ability to to override autolinking from the linker command line.
- Source code compatibility, where possible, with "comment lib" pragmas in other
environments (MSVC in particular).
Dependent library support is implemented differently for ELF platforms than on
the other platforms. Primarily this difference is that on ELF we pass the
dependent library specifiers directly to the linker without manipulating them.
This is in contrast to other platforms where they are mapped to a specific
linker option by the compiler. This difference is a result of the greater
variety of ELF linkers and the fact that ELF linkers tend to handle libraries in
a more complicated fashion than on other platforms. This forces us to defer
handling the specifiers to the linker.
In order to achieve a level of source code compatibility with other platforms
we have restricted this feature to work with libraries that meet the following
"reasonable" requirements:
1. There are no competing defined symbols in a given set of libraries, or
if they exist, the program owner doesn't care which is linked to their
program.
2. There may be circular dependencies between libraries.
The binary representation is a mergeable string section (SHF_MERGE,
SHF_STRINGS), called .deplibs, with custom type SHT_LLVM_DEPENDENT_LIBRARIES
(0x6fff4c04). The compiler forms this section by concatenating the arguments of
the "comment lib" pragmas and --dependent-library options in the order they are
encountered. Partial (-r, -Ur) links are handled by concatenating .deplibs
sections with the normal mergeable string section rules. As an example, #pragma
comment(lib, "foo") would result in:
.section ".deplibs","MS", at llvm_dependent_libraries,1
.asciz "foo"
For LTO, equivalent information to the contents of a the .deplibs section can be
retrieved by the LLD for bitcode input files.
LLD processes the dependent library specifiers in the following way:
1. Dependent libraries which are found from the specifiers in .deplibs sections
of relocatable object files are added when the linker decides to include that
file (which could itself be in a library) in the link. Dependent libraries
behave as if they were appended to the command line after all other options. As
a consequence the set of dependent libraries are searched last to resolve
symbols.
2. It is an error if a file cannot be found for a given specifier.
3. Any command line options in effect at the end of the command line parsing apply
to the dependent libraries, e.g. --whole-archive.
4. The linker tries to add a library or relocatable object file from each of the
strings in a .deplibs section by; first, handling the string as if it was
specified on the command line; second, by looking for the string in each of the
library search paths in turn; third, by looking for a lib<string>.a or
lib<string>.so (depending on the current mode of the linker) in each of the
library search paths.
5. A new command line option --no-dependent-libraries tells LLD to ignore the
dependent libraries.
Rationale for the above points:
1. Adding the dependent libraries last makes the process simple to understand
from a developers perspective. All linkers are able to implement this scheme.
2. Error-ing for libraries that are not found seems like better behavior than
failing the link during symbol resolution.
3. It seems useful for the user to be able to apply command line options which
will affect all of the dependent libraries. There is a potential problem of
surprise for developers, who might not realize that these options would apply
to these "invisible" input files; however, despite the potential for surprise,
this is easy for developers to reason about and gives developers the control
that they may require.
4. This algorithm takes into account all of the different ways that ELF linkers
find input files. The different search methods are tried by the linker in most
obvious to least obvious order.
5. I considered adding finer grained control over which dependent libraries were
ignored (e.g. MSVC has /nodefaultlib:<library>); however, I concluded that this
is not necessary: if finer control is required developers can fall back to using
the command line directly.
RFC thread: http://lists.llvm.org/pipermail/llvm-dev/2019-March/131004.html.
Differential Revision: https://reviews.llvm.org/D60274
Removed:
cfe/trunk/test/CodeGen/elf-linker-options.c
Modified:
cfe/trunk/lib/CodeGen/CodeGenModule.cpp
cfe/trunk/lib/CodeGen/CodeGenModule.h
cfe/trunk/lib/CodeGen/TargetInfo.cpp
cfe/trunk/test/CodeGen/dependent-lib.c
cfe/trunk/test/CodeGen/pragma-comment.c
cfe/trunk/test/Modules/autolink.m
Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=360984&r1=360983&r2=360984&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Thu May 16 20:44:15 2019
@@ -446,6 +446,19 @@ void CodeGenModule::Release() {
EmitModuleLinkOptions();
}
+ // On ELF we pass the dependent library specifiers directly to the linker
+ // without manipulating them. This is in contrast to other platforms where
+ // they are mapped to a specific linker option by the compiler. This
+ // difference is a result of the greater variety of ELF linkers and the fact
+ // that ELF linkers tend to handle libraries in a more complicated fashion
+ // than on other platforms. This forces us to defer handling the dependent
+ // libs to the linker.
+ if (!ELFDependentLibraries.empty()) {
+ auto *NMD = getModule().getOrInsertNamedMetadata("llvm.dependent-libraries");
+ for (auto *MD : ELFDependentLibraries)
+ NMD->addOperand(MD);
+ }
+
// Record mregparm value now so it is visible through rest of codegen.
if (Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86)
getModule().addModuleFlag(llvm::Module::Error, "NumRegisterParameters",
@@ -1903,17 +1916,18 @@ void CodeGenModule::AddDetectMismatch(St
LinkerOptionsMetadata.push_back(llvm::MDNode::get(getLLVMContext(), MDOpts));
}
-void CodeGenModule::AddELFLibDirective(StringRef Lib) {
+void CodeGenModule::AddDependentLib(StringRef Lib) {
auto &C = getLLVMContext();
- LinkerOptionsMetadata.push_back(llvm::MDNode::get(
- C, {llvm::MDString::get(C, "lib"), llvm::MDString::get(C, Lib)}));
-}
+ if (getTarget().getTriple().isOSBinFormatELF()) {
+ ELFDependentLibraries.push_back(
+ llvm::MDNode::get(C, llvm::MDString::get(C, Lib)));
+ return;
+ }
-void CodeGenModule::AddDependentLib(StringRef Lib) {
llvm::SmallString<24> Opt;
getTargetCodeGenInfo().getDependentLibraryOption(Lib, Opt);
auto *MDOpts = llvm::MDString::get(getLLVMContext(), Opt);
- LinkerOptionsMetadata.push_back(llvm::MDNode::get(getLLVMContext(), MDOpts));
+ LinkerOptionsMetadata.push_back(llvm::MDNode::get(C, MDOpts));
}
/// Add link options implied by the given module, including modules
@@ -1936,7 +1950,6 @@ static void addLinkOptionsPostorder(Code
// described by this module.
llvm::LLVMContext &Context = CGM.getLLVMContext();
bool IsELF = CGM.getTarget().getTriple().isOSBinFormatELF();
- bool IsPS4 = CGM.getTarget().getTriple().isPS4();
// For modules that use export_as for linking, use that module
// name instead.
@@ -1956,7 +1969,7 @@ static void addLinkOptionsPostorder(Code
}
// Link against a library.
- if (IsELF && !IsPS4) {
+ if (IsELF) {
llvm::Metadata *Args[2] = {
llvm::MDString::get(Context, "lib"),
llvm::MDString::get(Context, Mod->LinkLibraries[I - 1].Library),
@@ -5197,10 +5210,6 @@ void CodeGenModule::EmitTopLevelDecl(Dec
AppendLinkerOptions(PCD->getArg());
break;
case PCK_Lib:
- if (getTarget().getTriple().isOSBinFormatELF() &&
- !getTarget().getTriple().isPS4())
- AddELFLibDirective(PCD->getArg());
- else
AddDependentLib(PCD->getArg());
break;
case PCK_Compiler:
Modified: cfe/trunk/lib/CodeGen/CodeGenModule.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.h?rev=360984&r1=360983&r2=360984&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.h (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.h Thu May 16 20:44:15 2019
@@ -465,9 +465,12 @@ private:
/// have been emitted.
llvm::SmallPtrSet<clang::Module *, 16> EmittedModuleInitializers;
- /// A vector of metadata strings.
+ /// A vector of metadata strings for linker options.
SmallVector<llvm::MDNode *, 16> LinkerOptionsMetadata;
+ /// A vector of metadata strings for dependent libraries for ELF.
+ SmallVector<llvm::MDNode *, 16> ELFDependentLibraries;
+
/// @name Cache for Objective-C runtime types
/// @{
@@ -1152,11 +1155,9 @@ public:
/// Appends a detect mismatch command to the linker options.
void AddDetectMismatch(StringRef Name, StringRef Value);
- /// Appends a dependent lib to the "llvm.linker.options" metadata
- /// value.
+ /// Appends a dependent lib to the appropriate metadata value.
void AddDependentLib(StringRef Lib);
- void AddELFLibDirective(StringRef Lib);
llvm::GlobalVariable::LinkageTypes getFunctionLinkage(GlobalDecl GD);
Modified: cfe/trunk/lib/CodeGen/TargetInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/TargetInfo.cpp?rev=360984&r1=360983&r2=360984&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/TargetInfo.cpp (original)
+++ cfe/trunk/lib/CodeGen/TargetInfo.cpp Thu May 16 20:44:15 2019
@@ -2348,22 +2348,6 @@ public:
}
};
-class PS4TargetCodeGenInfo : public X86_64TargetCodeGenInfo {
-public:
- PS4TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT, X86AVXABILevel AVXLevel)
- : X86_64TargetCodeGenInfo(CGT, AVXLevel) {}
-
- void getDependentLibraryOption(llvm::StringRef Lib,
- llvm::SmallString<24> &Opt) const override {
- Opt = "\01";
- // If the argument contains a space, enclose it in quotes.
- if (Lib.find(" ") != StringRef::npos)
- Opt += "\"" + Lib.str() + "\"";
- else
- Opt += Lib;
- }
-};
-
static std::string qualifyWindowsLibrary(llvm::StringRef Lib) {
// If the argument does not end in .lib, automatically add the suffix.
// If the argument contains a space, enclose it in quotes.
@@ -9493,8 +9477,6 @@ const TargetCodeGenInfo &CodeGenModule::
switch (Triple.getOS()) {
case llvm::Triple::Win32:
return SetCGInfo(new WinX86_64TargetCodeGenInfo(Types, AVXLevel));
- case llvm::Triple::PS4:
- return SetCGInfo(new PS4TargetCodeGenInfo(Types, AVXLevel));
default:
return SetCGInfo(new X86_64TargetCodeGenInfo(Types, AVXLevel));
}
Modified: cfe/trunk/test/CodeGen/dependent-lib.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/dependent-lib.c?rev=360984&r1=360983&r2=360984&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/dependent-lib.c (original)
+++ cfe/trunk/test/CodeGen/dependent-lib.c Thu May 16 20:44:15 2019
@@ -1,12 +1,12 @@
// RUN: %clang_cc1 %s --dependent-lib=msvcrt -triple thumbv7-windows -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 %s --dependent-lib=msvcrt -triple i686-pc-win32 -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 %s --dependent-lib=msvcrt -triple x86_64-pc-win32 -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s --dependent-lib=msvcrt -triple i686-pc-linux -emit-llvm -o - | FileCheck -check-prefix LINUX %s
+// RUN: %clang_cc1 %s --dependent-lib=msvcrt -triple i686-pc-linux -emit-llvm -o - | FileCheck -check-prefix LINUX %s --implicit-check-not llvm.linker.options
// CHECK: !llvm.linker.options = !{![[msvcrt:[0-9]+]]}
// CHECK: ![[msvcrt]] = !{!"/DEFAULTLIB:msvcrt.lib"}
-// LINUX: !llvm.linker.options = !{![[msvcrt:[0-9]+]]}
-// LINUX: ![[msvcrt]] = !{!"-lmsvcrt"}
+// LINUX: !llvm.dependent-libraries = !{![[msvcrt:[0-9]+]]}
+// LINUX: ![[msvcrt]] = !{!"msvcrt"}
int f();
Removed: cfe/trunk/test/CodeGen/elf-linker-options.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/elf-linker-options.c?rev=360983&view=auto
==============================================================================
--- cfe/trunk/test/CodeGen/elf-linker-options.c (original)
+++ cfe/trunk/test/CodeGen/elf-linker-options.c (removed)
@@ -1,7 +0,0 @@
-// RUN: %clang_cc1 -triple i686---elf -emit-llvm %s -o - | FileCheck %s
-
-#pragma comment(lib, "alpha")
-
-// CHECK: !llvm.linker.options = !{[[NODE:![0-9]+]]}
-// CHECK: [[NODE]] = !{!"lib", !"alpha"}
-
Modified: cfe/trunk/test/CodeGen/pragma-comment.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/pragma-comment.c?rev=360984&r1=360983&r2=360984&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/pragma-comment.c (original)
+++ cfe/trunk/test/CodeGen/pragma-comment.c Thu May 16 20:44:15 2019
@@ -1,9 +1,9 @@
// RUN: %clang_cc1 %s -triple i686-pc-win32 -fms-extensions -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 %s -triple thumbv7-windows -fms-extensions -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 %s -triple x86_64-pc-win32 -fms-extensions -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s -triple thumbv7-linux-gnueabihf -fms-extensions -emit-llvm -o - | FileCheck -check-prefix LINUX %s
-// RUN: %clang_cc1 %s -triple i686-pc-linux -fms-extensions -emit-llvm -o - | FileCheck -check-prefix LINUX %s
-// RUN: %clang_cc1 %s -triple x86_64-scei-ps4 -fms-extensions -emit-llvm -o - | FileCheck -check-prefix PS4 %s
+// RUN: %clang_cc1 %s -triple thumbv7-linux-gnueabihf -fms-extensions -emit-llvm -o - | FileCheck -check-prefix ELF %s --implicit-check-not llvm.linker.options
+// RUN: %clang_cc1 %s -triple i686-pc-linux -fms-extensions -emit-llvm -o - | FileCheck -check-prefix ELF %s --implicit-check-not llvm.linker.options
+// RUN: %clang_cc1 %s -triple x86_64-scei-ps4 -fms-extensions -emit-llvm -o - | FileCheck -check-prefix ELF %s --implicit-check-not llvm.linker.options
// RUN: %clang_cc1 %s -triple aarch64-windows-msvc -fms-extensions -emit-llvm -o - | FileCheck %s
#pragma comment(lib, "msvcrt.lib")
@@ -23,11 +23,10 @@
// CHECK: ![[bar]] = !{!" /bar=2"}
// CHECK: ![[foo]] = !{!" /foo=\22foo bar\22"}
-// LINUX: !{!"lib", !"msvcrt.lib"}
-// LINUX: !{!"lib", !"kernel32"}
-// LINUX: !{!"lib", !"USER32.LIB"}
-
-// PS4: !{!"\01msvcrt.lib"}
-// PS4: !{!"\01kernel32"}
-// PS4: !{!"\01USER32.LIB"}
-// PS4: !{!"\01\22with space\22"}
+// ELF: !llvm.dependent-libraries = !{![[msvcrt:[0-9]+]], ![[kernel32:[0-9]+]], ![[USER32:[0-9]+]], ![[space:[0-9]+]]
+// ELF: ![[msvcrt]] = !{!"msvcrt.lib"}
+// ELF: ![[kernel32]] = !{!"kernel32"}
+// ELF: ![[USER32]] = !{!"USER32.LIB"}
+// ELF: ![[space]] = !{!"with space"}
+// ELF-NOT: bar
+// ELF-NOT: foo
Modified: cfe/trunk/test/Modules/autolink.m
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/autolink.m?rev=360984&r1=360983&r2=360984&view=diff
==============================================================================
--- cfe/trunk/test/Modules/autolink.m (original)
+++ cfe/trunk/test/Modules/autolink.m Thu May 16 20:44:15 2019
@@ -37,9 +37,9 @@ int use_autolink_sub3() {
// NOTE: "autolink_sub" is intentionally not linked.
// CHECK: !llvm.linker.options = !{![[AUTOLINK_PCH:[0-9]+]], ![[AUTOLINK_FRAMEWORK:[0-9]+]], ![[AUTOLINK:[0-9]+]], ![[DEPENDSONMODULE:[0-9]+]], ![[MODULE:[0-9]+]], ![[NOUMBRELLA:[0-9]+]]}
-// CHECK: ![[AUTOLINK_PCH]] = !{!"{{(\\01|-l|/DEFAULTLIB:|lib", !")}}autolink_from_pch{{(\.lib)?}}"}
+// CHECK: ![[AUTOLINK_PCH]] = !{!"{{(-l|/DEFAULTLIB:|lib", !")}}autolink_from_pch{{(\.lib)?}}"}
// CHECK: ![[AUTOLINK_FRAMEWORK]] = !{!"-framework", !"autolink_framework"}
-// CHECK: ![[AUTOLINK]] = !{!"{{(\\01|-l|/DEFAULTLIB:|lib", !")}}autolink{{(\.lib)?}}"}
+// CHECK: ![[AUTOLINK]] = !{!"{{(-l|/DEFAULTLIB:|lib", !")}}autolink{{(\.lib)?}}"}
// CHECK: ![[DEPENDSONMODULE]] = !{!"-framework", !"DependsOnModule"}
// CHECK: ![[MODULE]] = !{!"-framework", !"Module"}
// CHECK: ![[NOUMBRELLA]] = !{!"-framework", !"NoUmbrella"}
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