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[clang] Add option for -nolibc in Driver/ToolChains/Baremetal.cpp #145700

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[clang] Add option for -nolibc in Driver/ToolChains/Baremetal.cpp #145700

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97c87ce
[clang] Add option for -nolibc in Driver/ToolChains/Baremetal.cpp
saturn691 Jun 25, 2025
a433cb7
Add lit tests in clang/test/Driver/baremetal.cpp
saturn691 Jun 26, 2025
840941e
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saturn691 Jun 27, 2025
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saturn691 Jun 27, 2025
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22 changes: 12 additions & 10 deletions clang/lib/Driver/ToolChains/BareMetal.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -339,15 +339,15 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
};

switch (GetCXXStdlibType(DriverArgs)) {
case ToolChain::CST_Libcxx: {
SmallString<128> P(D.Dir);
llvm::sys::path::append(P, "..", "include");
AddCXXIncludePath(P);
break;
}
case ToolChain::CST_Libstdcxx:
// We only support libc++ toolchain installation.
break;
case ToolChain::CST_Libcxx: {
SmallString<128> P(D.Dir);
llvm::sys::path::append(P, "..", "include");
AddCXXIncludePath(P);
break;
}
case ToolChain::CST_Libstdcxx:
// We only support libc++ toolchain installation.
break;
}

std::string SysRoot(computeSysRoot());
Expand Down Expand Up @@ -498,7 +498,9 @@ void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
AddRunTimeLibs(TC, D, CmdArgs, Args);

CmdArgs.push_back("-lc");
if (!Args.hasArg(options::OPT_nolibc)) {
CmdArgs.push_back("-lc");
}
}

if (D.isUsingLTO())
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10 changes: 10 additions & 0 deletions clang/test/Driver/baremetal.cpp
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Expand Up @@ -143,6 +143,16 @@
// RUN: | FileCheck %s --check-prefix=CHECK-RTLIB-GCC
// CHECK-RTLIB-GCC: -lgcc

// RUN: %clang -### --target=arm-none-eabi -nolibc %s 2>&1 \
// RUN: | FileCheck %s --check-prefix=CHECK-NOLIBC
// CHECK-NOLIBC-NOT: "-lc"
// CHECK-NOLIBC: "{{[^"]*}}libclang_rt.builtins.a"
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The runtime library is not relevant to this test so I'd omit this line.

Suggested change
// CHECK-NOLIBC: "{{[^"]*}}libclang_rt.builtins.a"

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@saturn691 saturn691 Jun 27, 2025 •
edited
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The thing I'm trying to test is the follows, I think it still makes sense to test libclang_rt.builtings.a (replace libgcc with compiler-rt):

-nolibc
Do not use the C library or system libraries tightly coupled with it when linking. Still link with the startup files, libgcc or toolchain provided language support libraries such as libgnat, libgfortran or libstdc++ unless options preventing their inclusion are used as well.

-nostdlib
Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored.

The compiler may generate calls to memcmp, memset, memcpy and memmove. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified.

One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a, a library of internal subroutines which GCC uses to overcome shortcomings of particular machines, or special needs for some languages.

Reference: https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html#index-nolibc


// RUN: %clang -### --target=arm-none-eabi -nostdlib %s 2>&1 \
// RUN: | FileCheck %s --check-prefix=CHECK-NOSTDLIB
// CHECK-NOSTDLIB-NOT: "-lc"
// CHECK-NOSTDLIB-NOT: "{{[^"]*}}libclang_rt.builtins.a"
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Ditto here.

Suggested change
// CHECK-NOSTDLIB-NOT: "{{[^"]*}}libclang_rt.builtins.a"

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Ditto previous comment


// RUN: %clang -### --target=arm-none-eabi -v %s 2>&1 \
// RUN: | FileCheck %s --check-prefix=CHECK-SYSROOT-INC
// CHECK-SYSROOT-INC-NOT: "-internal-isystem" "include"
Expand Down