cannot build LLVM for `arm-freebsd-eabihf`

[HomuHomu833]

Zig Version

0.16.0-dev.164+bc7955306

Steps to Reproduce and Observed Behavior

idk just trying to compile LLVM as is with using Zig's LLVM backend, maybe can be upstream issue?

workflow:
https://github.com/HomuHomu833/llvm-custom/blob/main/.github/workflows/build_llvm_bsd.yml

workflow run:
https://github.com/HomuHomu833-garbage/llvm-custom-experimental/actions/runs/17573860945/job/49914854471

error:

FAILED: [code=1] bin/llvm-min-tblgen 
: && /home/runner/work/llvm-custom-experimental/llvm-custom-experimental/zig-as-llvm/bin/c++ -fstack-protector-strong -fsanitize=undefined -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Os -DNDEBUG -fno-pie -Wl,--color-diagnostics    -Wl,-z,origin  -Wl,--gc-sections utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/ARMTargetDefEmitter.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/Attributes.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/CodeGenIntrinsics.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/DirectiveEmitter.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/IntrinsicEmitter.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/RISCVTargetDefEmitter.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/SDNodeProperties.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/TableGen.cpp.o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/VTEmitter.cpp.o utils/TableGen/CMakeFiles/llvm-min-tblgen.dir/llvm-min-tblgen.cpp.o -o bin/llvm-min-tblgen  -Wl,-rpath,"\$ORIGIN/../lib"  lib/libLLVMSupport.a  lib/libLLVMTableGen.a  -lrt  -lm  /home/runner/work/llvm-custom-experimental/llvm-custom-experimental/output/arm-freebsd-eabihf/lib/libz.a  /home/runner/work/llvm-custom-experimental/llvm-custom-experimental/output/arm-freebsd-eabihf/lib/libzstd.a  lib/libLLVMDemangle.a && :
ld.lld: error: undefined symbol: __aeabi_read_tp
>>> referenced by PrettyStackTrace.cpp
>>>               PrettyStackTrace.cpp.o:(llvm::PrettyStackTraceEntry::PrettyStackTraceEntry()) in archive lib/libLLVMSupport.a
>>> referenced by PrettyStackTrace.cpp
>>>               PrettyStackTrace.cpp.o:(printForSigInfoIfNeeded()) in archive lib/libLLVMSupport.a
>>> referenced by PrettyStackTrace.cpp
>>>               PrettyStackTrace.cpp.o:(llvm::PrettyStackTraceEntry::~PrettyStackTraceEntry()) in archive lib/libLLVMSupport.a
>>> referenced 2 more times

Expected Behavior

to LLVM compile

[alexrp]

There's way too much going on in that workflow for me to diagnose anything based on that.

That said, just going off the error, this is an interesting case. It looks like, on FreeBSD, __aeabi_read_tp is provided by libc, but it's in the FBSDprivate_1.0 namespace which we explicitly exclude from our stub libc. But it's a symbol that's part of the Arm EABI, so "private" or not, the compiler will use it. This is a pretty compelling argument for reconsidering #24841.

[alexrp]

I'll also note that we're able to build LLVM for arm-freebsd-eabihf in zig-bootstrap. I don't know why it's not a problem there - perhaps this stack trace code is excluded?

[alexrp]

This is a pretty compelling argument for reconsidering #24841.

Then again: https://github.com/freebsd/freebsd-src/blob/5ca390f03bc63bccc8952313d536fd4bcabf2cab/lib/libc/arm/gen/__aeabi_read_tp.S#L32

zig/lib/compiler_rt/arm.zig

Lines 40 to 42 in fb3afc8

	if (builtin.os.tag == .linux) {
	@export(&__aeabi_read_tp, .{ .name = "__aeabi_read_tp", .linkage = common.linkage, .visibility = common.visibility });
	}

zig/lib/compiler_rt/arm.zig

Lines 119 to 127 in fb3afc8

	// This function can only clobber r0 according to the ABI
	pub fn __aeabi_read_tp() callconv(.naked) void {
	@setRuntimeSafety(false);
	asm volatile (
	\\ mrc p15, 0, r0, c13, c0, 3
	\\ bx lr
	);
	unreachable;
	}

Looks like we could just export this for FreeBSD too and it'll be fine.

[HomuHomu833]

I'll also note that we're able to build LLVM for arm-freebsd-eabihf in zig-bootstrap. I don't know why it's not a problem there - perhaps this stack trace code is excluded?

it's 100% due to UBsan I use then but I'm kinda forced to, if I don't include -fsanitize=undefined CMake (or LLVM?) refuses to see zlib and zstd.