riscv64-linux-musl fails to build: cannot link object files with different floating-point ABI

[andrewrk]

Extracted from #4485. See also #4456.

#include <iostream>

int main(int argc, char **argv) {
    std::cout << "Hello World!" << std::endl;
    return 0;
}

$ ./zig build-exe --c-source hello.cpp -lc++ -lc -target riscv64-linux-musl
lld: error: /home/andy/.cache/zig/stage1/o/rWRKkwM2cJJ4c6gEz91MCtccTwDwRvYtWBCJbHf31wuzT5fYo1koVTUiLWnemlaF/libcompiler_rt.a(/home/andy/.cache/zig/stage1/o/rWRKkwM2cJJ4c6gEz91MCtccTwDwRvYtWBCJbHf31wuzT5fYo1koVTUiLWnemlaF/compiler_rt.o): cannot link object files with different floating-point ABI

[LemonBoy]

Check this out.

[andrewrk]

I tried this diff:

diff --git a/src/codegen.cpp b/src/codegen.cpp
index c9e67dcac..b2210ba0c 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -8940,10 +8940,17 @@ static void init(CodeGen *g) {
         fprintf(stderr, "name=%s target_specific_cpu_args=%s\n", buf_ptr(g->root_out_name), target_specific_cpu_args);
         fprintf(stderr, "name=%s target_specific_features=%s\n", buf_ptr(g->root_out_name), target_specific_features);
     }
+
+    // TODO handle float ABI better- it should depend on the ABI portion of std.Target
+    ZigLLVMABIType float_abi = ZigLLVMABITypeDefault;
+    if (g->zig_target->os == OsLinux && target_is_riscv(g->zig_target)) {
+        // RISC-V Linux defaults to ilp32d/lp64d
+        float_abi = ZigLLVMABITypeHard;
+    }
     
     g->target_machine = ZigLLVMCreateTargetMachine(target_ref, buf_ptr(&g->llvm_triple_str),
             target_specific_cpu_args, target_specific_features, opt_level, reloc_mode,
-            to_llvm_code_model(g), g->function_sections);
+            to_llvm_code_model(g), g->function_sections, float_abi);
 
     g->target_data_ref = LLVMCreateTargetDataLayout(g->target_machine);
 
diff --git a/src/zig_llvm.cpp b/src/zig_llvm.cpp
index 5569f90cd..e06683ef7 100644
--- a/src/zig_llvm.cpp
+++ b/src/zig_llvm.cpp
@@ -100,7 +100,7 @@ static const bool assertions_on = false;
 
 LLVMTargetMachineRef ZigLLVMCreateTargetMachine(LLVMTargetRef T, const char *Triple,
     const char *CPU, const char *Features, LLVMCodeGenOptLevel Level, LLVMRelocMode Reloc,
-    LLVMCodeModel CodeModel, bool function_sections)
+    LLVMCodeModel CodeModel, bool function_sections, ZigLLVMABIType float_abi)
 {
     Optional<Reloc::Model> RM;
     switch (Reloc){
@@ -147,6 +147,17 @@ LLVMTargetMachineRef ZigLLVMCreateTargetMachine(LLVMTargetRef T, const char *Tri
 
     TargetOptions opt;
     opt.FunctionSections = function_sections;
+    switch (float_abi) {
+        case ZigLLVMABITypeDefault:
+            opt.FloatABIType = FloatABI::Default;
+            break;
+        case ZigLLVMABITypeSoft:
+            opt.FloatABIType = FloatABI::Soft;
+            break;
+        case ZigLLVMABITypeHard:
+            opt.FloatABIType = FloatABI::Hard;
+            break;
+    }
 
     TargetMachine *TM = reinterpret_cast<Target*>(T)->createTargetMachine(Triple, CPU, Features, opt, RM, CM,
             OL, JIT);
diff --git a/src/zig_llvm.h b/src/zig_llvm.h
index c2c4b4dd7..24e14f2f7 100644
--- a/src/zig_llvm.h
+++ b/src/zig_llvm.h
@@ -51,9 +51,16 @@ ZIG_EXTERN_C bool ZigLLVMTargetMachineEmitToFile(LLVMTargetMachineRef targ_machi
         bool is_small, bool time_report,
         const char *asm_filename, const char *bin_filename, const char *llvm_ir_filename);
 
+
+enum ZigLLVMABIType {
+    ZigLLVMABITypeDefault, // Target-specific (either soft or hard depending on triple, etc).
+    ZigLLVMABITypeSoft,    // Soft float.
+    ZigLLVMABITypeHard     // Hard float.
+};
+
 ZIG_EXTERN_C LLVMTargetMachineRef ZigLLVMCreateTargetMachine(LLVMTargetRef T, const char *Triple,
     const char *CPU, const char *Features, LLVMCodeGenOptLevel Level, LLVMRelocMode Reloc,
-    LLVMCodeModel CodeModel, bool function_sections);
+    LLVMCodeModel CodeModel, bool function_sections, ZigLLVMABIType float_abi);
 
 ZIG_EXTERN_C LLVMTypeRef ZigLLVMTokenTypeInContext(LLVMContextRef context_ref);
 

Still got the error "cannot link object files with different floating-point ABI".

I wonder what the clang argumentsl -mabi=ilp32d / -mabi=lp64d are doing in terms of the LLVM API.

[andrewrk]

@luismarques do you have any clues? What LLVM API do we need to match clang's behavior here?

[LemonBoy]

The -mabi switch translates to this field in TargetOptions.MCOptions. The float ABI switch is also nice to have.

[luismarques]

@luismarques do you have any clues? What LLVM API do we need to match clang's behavior here?

Sorry, with the UK lockdown and the nurseries closing my available time has dramatically diminished, so I haven't been able to look into this.

[andrewrk]

No worries @luismarques - btw this issue was solved with 11b50e3