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merged 2 commits into from
Oct 21, 2025
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[Clang][LLVM] Support for Fuchsia on ARM #163848

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[Clang][LLVM] Support for Fuchsia on ARM
petrhosek Mar 17, 2025
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petrhosek Oct 16, 2025
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4 changes: 4 additions & 0 deletions clang/lib/Basic/Targets.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -222,6 +222,8 @@ std::unique_ptr<TargetInfo> AllocateTarget(const llvm::Triple &Triple,
return std::make_unique<OHOSTargetInfo<ARMleTargetInfo>>(Triple, Opts);
case llvm::Triple::FreeBSD:
return std::make_unique<FreeBSDTargetInfo<ARMleTargetInfo>>(Triple, Opts);
case llvm::Triple::Fuchsia:
return std::make_unique<FuchsiaTargetInfo<ARMleTargetInfo>>(Triple, Opts);
case llvm::Triple::NetBSD:
return std::make_unique<NetBSDTargetInfo<ARMleTargetInfo>>(Triple, Opts);
case llvm::Triple::OpenBSD:
Expand Down Expand Up @@ -254,6 +256,8 @@ std::unique_ptr<TargetInfo> AllocateTarget(const llvm::Triple &Triple,
return std::make_unique<AppleMachOARMTargetInfo>(Triple, Opts);

switch (os) {
case llvm::Triple::Fuchsia:
return std::make_unique<FuchsiaTargetInfo<ARMbeTargetInfo>>(Triple, Opts);
case llvm::Triple::Linux:
return std::make_unique<LinuxTargetInfo<ARMbeTargetInfo>>(Triple, Opts);
case llvm::Triple::NetBSD:
Expand Down
3 changes: 2 additions & 1 deletion clang/lib/Basic/Targets/ARM.cpp
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Expand Up @@ -260,6 +260,7 @@ ARMTargetInfo::ARMTargetInfo(const llvm::Triple &Triple,
: TargetInfo(Triple), FPMath(FP_Default), IsAAPCS(true), LDREX(0),
HW_FP(0) {
bool IsFreeBSD = Triple.isOSFreeBSD();
bool IsFuchsia = Triple.isOSFuchsia();
bool IsOpenBSD = Triple.isOSOpenBSD();
bool IsNetBSD = Triple.isOSNetBSD();
bool IsHaiku = Triple.isOSHaiku();
Expand Down Expand Up @@ -332,7 +333,7 @@ ARMTargetInfo::ARMTargetInfo(const llvm::Triple &Triple,
default:
if (IsNetBSD)
setABI("apcs-gnu");
else if (IsFreeBSD || IsOpenBSD || IsHaiku || IsOHOS)
else if (IsFreeBSD || IsFuchsia || IsOpenBSD || IsHaiku || IsOHOS)
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I haven't actually been able to discern how aapcs-linux actually differs from aapcs or aapcs-vfp.

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The resources I found when researching this is https://wiki.debian.org/ArmEabiPort and https://kanj.github.io/elfs/book/armMusl/cross-tools/abi.html and according to those the only difference is enum size: aapcs defines enums to be a variable sized type, while with aapcs-linux they are always ints (4 bytes).

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Ah right, that is the default for -fshort-enum IOW. I don't know why Linux long ago diverged from the clearly-published AAPCS on this, but for us matching Linux ABIs for this sort of detail (things likely relevant to porting code from arm-linux distinct from direct OS dependencies) is more important than published standards or CPU vendor's recommendations. It would be nice if the code made it easier to discover that aapcs-linux means aapcs + -fshort-enum.

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It's especially notable if not only the glibc-based Linux configurations, but musl, android, etc. are also still doing -fshort-enum / aapcs-linux then there is no question that Fuchsia wants to follow them all. If e.g. Android differed from -gnueabihf on this then we might consider whether to align with one or the other.

setABI("aapcs-linux");
else
setABI("aapcs");
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5 changes: 5 additions & 0 deletions clang/lib/Driver/ToolChains/Arch/ARM.cpp
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Expand Up @@ -290,6 +290,8 @@ void arm::setArchNameInTriple(const Driver &D, const ArgList &Args,
// Thumb2 is the default for V7 on Darwin.
(llvm::ARM::parseArchVersion(Suffix) == 7 &&
Triple.isOSBinFormatMachO()) ||
// Thumb2 is the default for Fuchsia.
Triple.isOSFuchsia() ||
// FIXME: this is invalid for WindowsCE
Triple.isOSWindows();

Expand Down Expand Up @@ -452,6 +454,9 @@ arm::FloatABI arm::getDefaultFloatABI(const llvm::Triple &Triple) {
case llvm::Triple::OpenBSD:
return FloatABI::SoftFP;

case llvm::Triple::Fuchsia:
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I'm wondering about this. It seems like it shouldn't be needed because the default case should already derive it correctly from Triple.getEnvironment().

But that's because I'm assuming that it should be GNUEABIHF, as it is in the most-similar existing target, arm*-linux-gnueabihf. In looking through what that's used for, it's frankly hard to tell. There are few checks for it directly. Things like isTargetEHABICompatible() definitely need to come up true, but I'm not sure what getEnvironment() value we have, and many of them are matched there.

Then there's isTargetGNUAEABI(), and isGNUEnvironment(). Those are tested in a bunch of places. Most of those we want to match what GNUEABIHF would give us. But in a few we might not (glibc-specific assumptions).

We can probably iterate to get all these corners right. But we'll probably need to actually investigate each use proactively and get the knobs right for the Fuchsia context rather than only tweak things as problems arise.

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For Fuchsia, on other architectures we don't specify any environment and I felt that requiring environment only for ARM (i.e. using arm-fuchsia-gnueabihf) would be inconsistent. Furthermore, as you pointed out, there are also place where GNUEABIHF behavior is likely undesirable for Fuchsia so I decide to instead directly conditionalize this and other places on OS rather than environment. I do expect we might need to another pass to make sure we get the right behavior, but at least for the initial version this change should be sufficient.

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Oh, I didn't realize that this "environment" was tied to the normalized triple text itself. I agree, we want the maximal triple to be something like armv8-unknown-fuchsia at most and canonically would tell people to just use --target=arm-fuchsia for sure. I just meant that it seemed likely that more actual choices would match what ::GNUEABIHF is used for than not, at a guess. (We are going for pretty much the armv7-linux-gnueabihf ABI in terms of most things: ISA support, code-gen details, C-visible core ABI issues, though armv8+... for -march and some differences in libc ABI expectations.)

return FloatABI::Hard;

default:
if (Triple.isOHOSFamily())
return FloatABI::Soft;
Expand Down
2 changes: 2 additions & 0 deletions clang/test/Driver/arm-abi.c
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Expand Up @@ -31,6 +31,8 @@
// FreeBSD / OpenBSD default to aapcs-linux
// RUN: %clang -target arm--freebsd- %s -### -o %t.o 2>&1 \
// RUN: | FileCheck -check-prefix=CHECK-AAPCS-LINUX %s
// RUN: %clang -target arm--fuchsia- %s -### -o %t.o 2>&1 \
// RUN: | FileCheck -check-prefix=CHECK-AAPCS-LINUX %s
// RUN: %clang -target arm--openbsd- %s -### -o %t.o 2>&1 \
// RUN: | FileCheck -check-prefix=CHECK-AAPCS-LINUX %s
// RUN: %clang -target arm--haiku- %s -### -o %t.o 2>&1 \
Expand Down
9 changes: 9 additions & 0 deletions clang/test/Driver/fuchsia.c
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Expand Up @@ -2,6 +2,10 @@
// RUN: -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
// RUN: --sysroot=%S/platform -fuse-ld=ld 2>&1 \
// RUN: | FileCheck -check-prefixes=CHECK,CHECK-X86_64 %s
// RUN: %clang -### %s --target=arm-unknown-fuchsia \
// RUN: -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
// RUN: --sysroot=%S/platform -fuse-ld=ld 2>&1 \
// RUN: | FileCheck -check-prefixes=CHECK,CHECK-ARMV8A %s
// RUN: %clang -### %s --target=aarch64-unknown-fuchsia \
// RUN: -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
// RUN: --sysroot=%S/platform -fuse-ld=ld 2>&1 \
Expand All @@ -14,6 +18,10 @@
// RUN: -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
// RUN: --sysroot=%S/platform -fuse-ld=ld 2>&1 \
// RUN: | FileCheck -check-prefixes=CHECK,CHECK-X86_64 %s
// RUN: %clang -### %s --target=arm-fuchsia \
// RUN: -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
// RUN: --sysroot=%S/platform -fuse-ld=ld 2>&1 \
// RUN: | FileCheck -check-prefixes=CHECK,CHECK-ARMV8A %s
// RUN: %clang -### %s --target=aarch64-fuchsia \
// RUN: -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
// RUN: --sysroot=%S/platform -fuse-ld=ld 2>&1 \
Expand All @@ -24,6 +32,7 @@
// RUN: | FileCheck -check-prefixes=CHECK,CHECK-RISCV64 %s
// CHECK: "-cc1"
// CHECK-X86_64: "-triple" "x86_64-unknown-fuchsia"
// CHECK-ARMV8A: "-triple" "thumbv8a-unknown-fuchsia"
// CHECK-AARCH64: "-triple" "aarch64-unknown-fuchsia"
// CHECK-RISCV64: "-triple" "riscv64-unknown-fuchsia"
// CHECK: "-funwind-tables=2"
Expand Down
2 changes: 1 addition & 1 deletion llvm/include/llvm/IR/RuntimeLibcalls.h
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Expand Up @@ -238,7 +238,7 @@ struct RuntimeLibcallsInfo {

static bool hasAEABILibcalls(const Triple &TT) {
return TT.isTargetAEABI() || TT.isTargetGNUAEABI() ||
TT.isTargetMuslAEABI() || TT.isAndroid();
TT.isTargetMuslAEABI() || TT.isOSFuchsia() || TT.isAndroid();
}

LLVM_READONLY
Expand Down
3 changes: 2 additions & 1 deletion llvm/include/llvm/TargetParser/Triple.h
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Expand Up @@ -935,7 +935,8 @@ class Triple {
getEnvironment() == Triple::GNUEABIHF ||
getEnvironment() == Triple::GNUEABIHFT64 ||
getEnvironment() == Triple::OpenHOS ||
getEnvironment() == Triple::MuslEABIHF || isAndroid()) &&
getEnvironment() == Triple::MuslEABIHF || isOSFuchsia() ||
isAndroid()) &&
isOSBinFormatELF() && !isOSNetBSD();
}

Expand Down
4 changes: 2 additions & 2 deletions llvm/lib/Target/ARM/ARMISelLowering.cpp
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Expand Up @@ -1089,7 +1089,7 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM_,

// Register based DivRem for AEABI (RTABI 4.2)
if (TT.isTargetAEABI() || TT.isAndroid() || TT.isTargetGNUAEABI() ||
TT.isTargetMuslAEABI() || TT.isOSWindows()) {
TT.isTargetMuslAEABI() || TT.isOSFuchsia() || TT.isOSWindows()) {
setOperationAction(ISD::SREM, MVT::i64, Custom);
setOperationAction(ISD::UREM, MVT::i64, Custom);
HasStandaloneRem = false;
Expand Down Expand Up @@ -20574,7 +20574,7 @@ static TargetLowering::ArgListTy getDivRemArgList(
SDValue ARMTargetLowering::LowerDivRem(SDValue Op, SelectionDAG &DAG) const {
assert((Subtarget->isTargetAEABI() || Subtarget->isTargetAndroid() ||
Subtarget->isTargetGNUAEABI() || Subtarget->isTargetMuslAEABI() ||
Subtarget->isTargetWindows()) &&
Subtarget->isTargetFuchsia() || Subtarget->isTargetWindows()) &&
"Register-based DivRem lowering only");
unsigned Opcode = Op->getOpcode();
assert((Opcode == ISD::SDIVREM || Opcode == ISD::UDIVREM) &&
Expand Down
1 change: 1 addition & 0 deletions llvm/lib/Target/ARM/ARMSubtarget.h
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Expand Up @@ -343,6 +343,7 @@ class ARMSubtarget : public ARMGenSubtargetInfo {
bool isTargetWatchOS() const { return TargetTriple.isWatchOS(); }
bool isTargetWatchABI() const { return TargetTriple.isWatchABI(); }
bool isTargetDriverKit() const { return TargetTriple.isDriverKit(); }
bool isTargetFuchsia() const { return TargetTriple.isOSFuchsia(); }
bool isTargetLinux() const { return TargetTriple.isOSLinux(); }
bool isTargetNetBSD() const { return TargetTriple.isOSNetBSD(); }
bool isTargetWindows() const { return TargetTriple.isOSWindows(); }
Expand Down
6 changes: 4 additions & 2 deletions llvm/lib/TargetParser/ARMTargetParser.cpp
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Expand Up @@ -567,8 +567,8 @@ StringRef ARM::computeDefaultTargetABI(const Triple &TT) {
default:
if (TT.isOSNetBSD())
return "apcs-gnu";
if (TT.isOSFreeBSD() || TT.isOSOpenBSD() || TT.isOSHaiku() ||
TT.isOHOSFamily())
if (TT.isOSFreeBSD() || TT.isOSFuchsia() || TT.isOSOpenBSD() ||
TT.isOSHaiku() || TT.isOHOSFamily())
return "aapcs-linux";
return "aapcs";
}
Expand Down Expand Up @@ -648,6 +648,8 @@ StringRef ARM::getARMCPUForArch(const llvm::Triple &Triple, StringRef MArch) {
}
case llvm::Triple::OpenBSD:
return "cortex-a8";
case llvm::Triple::Fuchsia:
return "cortex-a53";
default:
switch (Triple.getEnvironment()) {
case llvm::Triple::EABIHF:
Expand Down