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[Clang][Driver] Expose relocation model as multilib flags #149132

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Merged
statham-arm merged 4 commits into from
Jul 18, 2025
Merged

[Clang][Driver] Expose relocation model as multilib flags #149132

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c45a519
[Clang][Driver] Expose relocation model as multilib flags
statham-arm Jul 14, 2025
02eada8
Add missing end of sentence in comment
statham-arm Jul 16, 2025
877d733
Move ROPI/RWPI into the Arm-specific function
statham-arm Jul 17, 2025
2568c65
Fix the test
statham-arm Jul 17, 2025
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37 changes: 37 additions & 0 deletions clang/lib/Driver/ToolChain.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -343,6 +343,7 @@ ToolChain::getMultilibFlags(const llvm::opt::ArgList &Args) const {
std::vector<std::string> Result;
const llvm::Triple Triple(ComputeEffectiveClangTriple(Args));
Result.push_back("--target=" + Triple.str());
bool IsARM = false;

switch (Triple.getArch()) {
case llvm::Triple::aarch64:
Expand All @@ -355,6 +356,7 @@ ToolChain::getMultilibFlags(const llvm::opt::ArgList &Args) const {
case llvm::Triple::thumb:
case llvm::Triple::thumbeb:
getARMMultilibFlags(D, Triple, Args, Result);
IsARM = true; // for ROPI/RWPI below
break;
case llvm::Triple::riscv32:
case llvm::Triple::riscv64:
Expand All @@ -376,6 +378,41 @@ ToolChain::getMultilibFlags(const llvm::opt::ArgList &Args) const {
else
Result.push_back("-fexceptions");

// A difference of relocation model (absolutely addressed data, PIC, Arm
// ROPI/RWPI) is likely to change whether a particular multilib variant is
// compatible with a given link. Determine the relocation model of the
// current link, and add appropriate
{
RegisterEffectiveTriple TripleRAII(
*this, llvm::Triple(ComputeEffectiveClangTriple(Args)));

auto [RelocationModel, PICLevel, IsPIE] = tools::ParsePICArgs(*this, Args);

// ROPI and RWPI are only meaningful on Arm, so for other architectures, we
// expect never to find out they're enabled. But it seems confusing to add
// -fno-ropi and -fno-rwpi unconditionally to every other architecture's
// multilib flags, so instead we leave them out completely.
if (IsARM) {
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@vhscampos vhscampos Jul 16, 2025

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Is there any way to move this Arm-only segment into getARMMultilibFlags? In theory, that function handles everything that is only relevant to Arm. So it's a more natural place to host this segment here.

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@statham-arm statham-arm Jul 17, 2025

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Done. In my early drafts I had the whole thing in getARMMultilibFlags, but moved it out once I realised that PIC needed to be handled as well as ROPI/RWPI. I've kept the calculation of the relocation model in the top-level function, and just passed the answer down into getARMMultilibFlags where it can add the Arm-specific options.

if (RelocationModel == llvm::Reloc::ROPI ||
RelocationModel == llvm::Reloc::ROPI_RWPI)
Result.push_back("-fropi");
else
Result.push_back("-fno-ropi");

if (RelocationModel == llvm::Reloc::RWPI ||
RelocationModel == llvm::Reloc::ROPI_RWPI)
Result.push_back("-frwpi");
else
Result.push_back("-fno-rwpi");
}

if (RelocationModel == llvm::Reloc::PIC_)
Result.push_back(IsPIE ? (PICLevel > 1 ? "-fPIE" : "-fpie")
: (PICLevel > 1 ? "-fPIC" : "-fpic"));
else
Result.push_back("-fno-pic");
}

// Sort and remove duplicates.
std::sort(Result.begin(), Result.end());
Result.erase(llvm::unique(Result), Result.end());
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19 changes: 19 additions & 0 deletions clang/test/Driver/print-multi-selection-flags.c
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Expand Up @@ -107,3 +107,22 @@
// CHECK-AARCH64-MULTILIB-CUSTOM-FLAG: --target=aarch64-unknown-none-eabi
// CHECK-MULTILIB-CUSTOM-FLAG-DAG: -fmultilib-flag=foo
// CHECK-MULTILIB-CUSTOM-FLAG-DAG: -fmultilib-flag=bar

// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fropi | FileCheck --check-prefixes=CHECK-ROPI,CHECK-NO-RWPI,CHECK-NO-PIC %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -frwpi | FileCheck --check-prefixes=CHECK-RWPI,CHECK-NO-ROPI,CHECK-NO-PIC %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fropi -frwpi | FileCheck --check-prefixes=CHECK-ROPI,CHECK-RWPI,CHECK-NO-PIC %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fno-ropi -fno-rwpi | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-NO-PIC %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-NO-PIC %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fpic | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIC1 %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fPIC | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIC2 %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fpie | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIE1 %s
// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=arm-none-eabi -march=armv7a -fPIE | FileCheck --check-prefixes=CHECK-NO-ROPI,CHECK-NO-RWPI,CHECK-PIE2 %s
// CHECK-ROPI: -fropi
// CHECK-NO-ROPI: -fno-ropi
// CHECK-RWPI: -frwpi
// CHECK-NO-RWPI: -fno-rwpi
// CHECK-PIC1: -fpic
// CHECK-PIC2: -fPIC
// CHECK-PIE1: -fpie
// CHECK-PIE2: -fPIE
// CHECK-NO-PIC: -fno-pic
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