From 8eda71616fecd098cbd7d2447859c8ac1315966f Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Tue, 2 Jun 2020 15:54:09 -0700 Subject: [PATCH] [Clang][A32/T32][Linux] -O1 implies -fomit-frame-pointer Summary: An upgrade of LLVM for CrOS [0] containing [1] triggered a bunch of errors related to writing to reserved registers for a Linux kernel's arm64 compat vdso (which is a aarch32 image). After a discussion on LKML [2], it was determined that -f{no-}omit-frame-pointer was not being specified. Comparing GCC and Clang [3], it becomes apparent that GCC defaults to omitting the frame pointer implicitly when optimizations are enabled, and Clang does not. ie. setting -O1 (or above) implies -fomit-frame-pointer. Clang was defaulting to -fno-omit-frame-pointer implicitly unless -fomit-frame-pointer was set explicitly. Why this becomes a problem is that the Linux kernel's arm64 compat vdso contains code that uses r7. r7 is used sometimes for the frame pointer (for example, when targeting thumb (-mthumb)). See useR7AsFramePointer() in llvm/llvm-project/llvm/lib/Target/ARM/ARMSubtarget.h. This is mostly for legacy/compatibility reasons, and the 2019 Q4 revision of the ARM AAPCS looks to standardize r11 as the frame pointer for aarch32, though this is not yet implemented in LLVM. Users that are reliant on the implicit value if unspecified when optimizations are enabled should explicitly choose -fomit-frame-pointer (new behavior) or -fno-omit-frame-pointer (old behavior). [0] https://bugs.chromium.org/p/chromium/issues/detail?id=1084372 [1] https://reviews.llvm.org/D76848 [2] https://lore.kernel.org/lkml/20200526173117.155339-1-ndesaulniers@google.com/ [3] https://godbolt.org/z/0oY39t Reviewers: kristof.beyls, psmith, danalbert, srhines, MaskRay, ostannard, efriedma Reviewed By: psmith, danalbert, srhines, MaskRay, efriedma Subscribers: efriedma, olista01, MaskRay, vhscampos, cfe-commits, llvm-commits, manojgupta, llozano, glider, hctim, eugenis, pcc, peter.smith, srhines Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D80828 --- clang/lib/Basic/Targets/ARM.cpp | 2 +- clang/lib/Driver/ToolChains/Clang.cpp | 12 ++++++++++-- clang/test/Driver/frame-pointer-elim.c | 28 ++++++++++++++++++++++++++++ llvm/docs/ReleaseNotes.rst | 6 ++++++ 4 files changed, 45 insertions(+), 3 deletions(-) diff --git a/clang/lib/Basic/Targets/ARM.cpp b/clang/lib/Basic/Targets/ARM.cpp index f02a9d3..08b6a9c 100644 --- a/clang/lib/Basic/Targets/ARM.cpp +++ b/clang/lib/Basic/Targets/ARM.cpp @@ -314,7 +314,7 @@ ARMTargetInfo::ARMTargetInfo(const llvm::Triple &Triple, // Maximum alignment for ARM NEON data types should be 64-bits (AAPCS) // as well the default alignment - if (IsAAPCS && (Triple.getEnvironment() != llvm::Triple::Android)) + if (IsAAPCS && !Triple.isAndroid()) DefaultAlignForAttributeAligned = MaxVectorAlign = 64; // Do force alignment of members that follow zero length bitfields. If diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp index 4dfc41c..d86fe49 100644 --- a/clang/lib/Driver/ToolChains/Clang.cpp +++ b/clang/lib/Driver/ToolChains/Clang.cpp @@ -7,6 +7,7 @@ //===----------------------------------------------------------------------===// #include "Clang.h" +#include "AMDGPU.h" #include "Arch/AArch64.h" #include "Arch/ARM.h" #include "Arch/Mips.h" @@ -15,11 +16,10 @@ #include "Arch/Sparc.h" #include "Arch/SystemZ.h" #include "Arch/X86.h" -#include "AMDGPU.h" #include "CommonArgs.h" #include "Hexagon.h" -#include "MSP430.h" #include "InputInfo.h" +#include "MSP430.h" #include "PS4CPU.h" #include "clang/Basic/CharInfo.h" #include "clang/Basic/CodeGenOptions.h" @@ -35,6 +35,7 @@ #include "llvm/Config/llvm-config.h" #include "llvm/Option/ArgList.h" #include "llvm/Support/CodeGen.h" +#include "llvm/Support/Compiler.h" #include "llvm/Support/Compression.h" #include "llvm/Support/FileSystem.h" #include "llvm/Support/Path.h" @@ -557,6 +558,13 @@ static bool useFramePointerForTargetByDefault(const ArgList &Args, Triple.isOSHurd()) { switch (Triple.getArch()) { // Don't use a frame pointer on linux if optimizing for certain targets. + case llvm::Triple::arm: + case llvm::Triple::armeb: + case llvm::Triple::thumb: + case llvm::Triple::thumbeb: + if (Triple.isAndroid()) + return true; + LLVM_FALLTHROUGH; case llvm::Triple::mips64: case llvm::Triple::mips64el: case llvm::Triple::mips: diff --git a/clang/test/Driver/frame-pointer-elim.c b/clang/test/Driver/frame-pointer-elim.c index 47c1c05..fd74da7 100644 --- a/clang/test/Driver/frame-pointer-elim.c +++ b/clang/test/Driver/frame-pointer-elim.c @@ -103,5 +103,33 @@ // RUN: %clang -### -target powerpc64 -S -O1 %s 2>&1 | \ // RUN: FileCheck --check-prefix=KEEP-NONE %s +// For AAarch32 (A32, T32) linux targets, default omit frame pointer when +// optimizations are enabled. +// RUN: %clang -### -target arm-linux-gnueabihf- -marm -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target arm-linux-gnueabihf- -mthumb -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target arm-linux-gnueabihf- -marm -mbig-endian -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target arm-linux-gnueabihf- -mthumb -mbig-endian -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target arm-linux-gnueabihf- -marm -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-NONE %s +// RUN: %clang -### -target arm-linux-gnueabihf- -mthumb -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-NONE %s +// RUN: %clang -### -target arm-linux-gnueabihf- -marm -mbig-endian -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-NONE %s +// RUN: %clang -### -target arm-linux-gnueabihf- -mthumb -mbig-endian -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-NONE %s +// For Android, keep the framepointers always. +// RUN: %clang -### -target armv7a-linux-androideabi- -marm -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target armv7a-linux-androideabi- -mthumb -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target armv7a-linux-androideabi- -marm -mbig-endian -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s +// RUN: %clang -### -target armv7a-linux-androideabi- -mthumb -mbig-endian -O1 -S %s 2>&1 | \ +// RUN: FileCheck --check-prefix=KEEP-ALL %s + void f0() {} void f1() { f0(); } diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst index a55d14c..ea1fad1 100644 --- a/llvm/docs/ReleaseNotes.rst +++ b/llvm/docs/ReleaseNotes.rst @@ -91,6 +91,12 @@ During this release ... * Implemented C-language intrinsics ```` for the CDE instruction set. +* Clang now defaults to ``-fomit-frame-pointer`` when targeting non-Android + Linux for arm and thumb when optimizations are enabled. Users that were + previously not specifying a value and relying on the implicit compiler + default may wish to specify ``-fno-omit-frame-pointer`` to get the old + behavior. This improves compatibility with GCC. + Changes to the MIPS Target -------------------------- -- 2.7.4