From 876df74dd47196a9ca3b4fff21ffb5441491a0a0 Mon Sep 17 00:00:00 2001 From: Shao-Ce SUN Date: Tue, 25 Apr 2023 15:18:29 +0800 Subject: [PATCH] [flang][driver] Allow main program to be in an archive Add --undefined=_QQmain to the link line, so that a Fortran main program will be included in the link job even if it is in an archive (unless we are building a shared object). For now, this is only applied to the Gnu toolchain. We also add a section on the linker invocation to docs/FlangDriver.md. The new tests require llvm-ar to construct an archive we can include in the link job. This is a new dependency for flang/test (which already depends on similar tools such as llvm-objdump). See discussions in https://github.com/llvm/llvm-project/issues/54787 which this patch fixes. Reviewed By: awarzynski Differential Revision: https://reviews.llvm.org/D134821 --- clang/lib/Driver/ToolChains/Gnu.cpp | 8 +++++++ flang/docs/FlangDriver.md | 42 ++++++++++++++++++++++++++++++------- flang/test/CMakeLists.txt | 1 + flang/test/Driver/link-c-main.c | 28 +++++++++++++++++++++++++ flang/test/Driver/link-f90-main.f90 | 23 ++++++++++++++++++++ flang/test/Driver/linker-flags.f90 | 15 +++++++++++++ 6 files changed, 110 insertions(+), 7 deletions(-) create mode 100644 flang/test/Driver/link-c-main.c create mode 100644 flang/test/Driver/link-f90-main.f90 diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp index b071632..c4a2761 100644 --- a/clang/lib/Driver/ToolChains/Gnu.cpp +++ b/clang/lib/Driver/ToolChains/Gnu.cpp @@ -598,6 +598,14 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA, // these dependencies need to be listed before the C runtime below (i.e. // AddRuntTimeLibs). if (D.IsFlangMode()) { + // A Fortran main program will be lowered to a function named _QQmain. Make + // _QQmain an undefined symbol, so that it's correctly resolved even when + // creating executable from archives. This is a workaround for how and where + // Flang's `main` is defined. For more context, see: + // * https://github.com/llvm/llvm-project/issues/54787 + if (!Args.hasArg(options::OPT_shared)) + CmdArgs.push_back("--undefined=_QQmain"); + addFortranRuntimeLibraryPath(ToolChain, Args, CmdArgs); addFortranRuntimeLibs(ToolChain, CmdArgs); CmdArgs.push_back("-lm"); diff --git a/flang/docs/FlangDriver.md b/flang/docs/FlangDriver.md index 6c2a473..9522e22 100644 --- a/flang/docs/FlangDriver.md +++ b/flang/docs/FlangDriver.md @@ -149,13 +149,6 @@ flang-new -ccc-print-phases -c file.f +- 3: backend, {2}, assembler 4: assembler, {3}, object ``` -Note that currently Flang does not support code-generation and `flang-new` will -fail during the second step above with the following error: -```bash -error: code-generation is not available yet -``` -The other phases are printed nonetheless when using `-ccc-print-phases`, as -that reflects what `clangDriver`, the library, will try to create and run. For actions specific to the frontend (e.g. preprocessing or code generation), a command to call the frontend driver is generated (more specifically, an @@ -205,6 +198,41 @@ is `ParseSyntaxOnlyAction`, which corresponds to `-fsyntax-only`. In other words, `flang-new -fc1 ` is equivalent to `flang-new -fc1 -fsyntax-only `. +## Linker invocation +> **_NOTE:_** Linker invocation through the `flang-new` driver is so far +> experimental. This section describes the currently intended design, and not +> necessarily what is implemented. + +Calling +```bash +flang-new -flang-experimental-exec prog.f90 +``` +will, on a high level, do two things: +* call the frontend driver, `flang-new -fc1`, to build the object file `prog.o` +* call the system linker to build the executable `a.out`. + +In both invocations, `flang-new` will add default options to the frontend driver +and the linker invocations. To see the exact invocations on your system, you can +call +```bash +flang-new -### prog.f90 +``` +The link line will contain a fair number of options, which will depend on your +system. Compared to when linking a C program with `clang`, the main additions +are (on GNU/linux), +* `--undefined=_QQmain`: A Fortran main program will appear in the corresponding + object file as a function called `_QQmain`. This flag makes sure that an + object file containing a Fortran main program (i.e., a symbol `_QQmain`) be + included in the linking also when it is bundled in an archive. +* `-lFortran_main`: The Fortran_main archive is part of Flang's runtime. It + exports the symbol `main`, i.e., a c main function, which will make some + initial configuration before calling `_QQmain`, and clean up before returning. +* `-lFortranRuntime`: Flang's Fortran runtime, containing, for example, + implementations of intrinsic functions. +* `-lFortranDecimal`: Part of Flang's runtime, containing routines for parsing + and formatting decimal numbers. +* `-lm`: Link with the math library, on which Flang's runtime depends. + ## The `flang-to-external-fc` script The `flang-to-external-fc` wrapper script for `flang-new` was introduced as a development tool and to facilitate testing. The `flang-to-external-fc` wrapper diff --git a/flang/test/CMakeLists.txt b/flang/test/CMakeLists.txt index 7d96a72..dbb0257 100644 --- a/flang/test/CMakeLists.txt +++ b/flang/test/CMakeLists.txt @@ -57,6 +57,7 @@ set(FLANG_TEST_DEPENDS fir-opt tco bbc + llvm-ar llvm-dis llvm-objdump llvm-readobj diff --git a/flang/test/Driver/link-c-main.c b/flang/test/Driver/link-c-main.c new file mode 100644 index 0000000..e681425 --- /dev/null +++ b/flang/test/Driver/link-c-main.c @@ -0,0 +1,28 @@ +/* +Test that an object file with a C main function can be linked to an executable +by Flang. + +For now, this test only covers the Gnu toolchain on Linux. + +REQUIRES: x86-registered-target || aarch64-registered-target || riscv64-registered-target +REQUIRES: system-linux, c-compiler + +RUN: %cc -c %s -o %t.o +RUN: %flang -target x86_64-unknown-linux-gnu %t.o -o %t.out -flang-experimental-exec +RUN: llvm-objdump --syms %t.out | FileCheck %s --implicit-check-not Fortran + +Test that it also works if the c-main is bundled in an archive. + +RUN: llvm-ar -r %t.a %t.o +RUN: %flang -target x86_64-unknown-linux-gnu %t.a -o %ta.out -flang-experimental-exec +RUN: llvm-objdump --syms %ta.out | FileCheck %s --implicit-check-not Fortran +*/ + +int main(void) { + return 0; +} + +/* +CHECK-DAG: F .text {{[a-f0-9]+}} main +CHECK-DAG: *UND* {{[a-f0-9]+}} _QQmain +*/ diff --git a/flang/test/Driver/link-f90-main.f90 b/flang/test/Driver/link-f90-main.f90 new file mode 100644 index 0000000..01f77f4 --- /dev/null +++ b/flang/test/Driver/link-f90-main.f90 @@ -0,0 +1,23 @@ +! Test that a fortran main program can be linked to an executable +! by flang. +! +! For now, this test only covers the Gnu toolchain on linux. + +!REQUIRES: x86-registered-target || aarch64-registered-target || riscv64-registered-target +!REQUIRES: system-linux + +! RUN: %flang_fc1 -emit-obj %s -o %t.o +! RUN: %flang -target x86_64-unknown-linux-gnu %t.o -o %t.out -flang-experimental-exec +! RUN: llvm-objdump --syms %t.out | FileCheck %s + +! Test that it also works if the program is bundled in an archive. + +! RUN: llvm-ar -r %t.a %t.o +! RUN: %flang -target x86_64-unknown-linux-gnu %t.a -o %ta.out -flang-experimental-exec +! RUN: llvm-objdump --syms %ta.out | FileCheck %s + +end program + +! CHECK-DAG: F .text {{[a-f0-9]+}} main +! CHECK-DAG: F .text {{[a-f0-9]+}} _QQmain +! CHECK-DAG: _FortranAProgramStart diff --git a/flang/test/Driver/linker-flags.f90 b/flang/test/Driver/linker-flags.f90 index e1350b74..f776d76 100644 --- a/flang/test/Driver/linker-flags.f90 +++ b/flang/test/Driver/linker-flags.f90 @@ -12,6 +12,14 @@ ! Make sure they're not added. ! RUN: %flang -### -flang-experimental-exec -target aarch64-windows-msvc %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,MSVC --implicit-check-not libcmt --implicit-check-not oldnames +! Check linker invocation to generate shared object (only GNU toolchain for now) +! Output should not contain any undefined reference to _QQmain since it is not +! considered a valid entry point for shared objects, which are usually specified +! using the bind attribute. +! RUN: %flang -### -flang-experimental-exec -shared -target x86_64-linux-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,GNU-SHARED --implicit-check-not _QQmain +! RUN: %flang -### -flang-experimental-exec -shared -target aarch64-linux-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,GNU-SHARED --implicit-check-not _QQmain +! RUN: %flang -### -flang-experimental-exec -shared -target riscv64-linux-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,GNU-SHARED --implicit-check-not _QQmain + ! Compiler invocation to generate the object file ! CHECK-LABEL: {{.*}} "-emit-obj" ! CHECK-SAME: "-o" "[[object_file:.*\.o]]" {{.*}}Inputs/hello.f90 @@ -23,6 +31,7 @@ ! executable and may find the GNU linker from MinGW or Cygwin. ! GNU-LABEL: "{{.*}}ld{{(\.exe)?}}" ! GNU-SAME: "[[object_file]]" +! GNU-SAME: --undefined=_QQmain ! GNU-SAME: -lFortran_main ! GNU-SAME: -lFortranRuntime ! GNU-SAME: -lFortranDecimal @@ -50,3 +59,9 @@ ! MSVC-SAME: FortranDecimal.lib ! MSVC-SAME: /subsystem:console ! MSVC-SAME: "[[object_file]]" + +! Linker invocation to generate a shared object +! GNU-SHARED-LABEL: "{{.*}}ld" +! GNU-SHARED-SAME: "[[object_file]]" +! GNU-SHARED-SAME: -lFortranRuntime +! GNU-SHARED-SAME: -lFortranDecimal -- 2.7.4