[E0668] Malformed inline assembly when building rustc

[varkor]

When running ./x.py build --stage 1, I now get the error:

error[E0668]: malformed inline assembly=======>                        ] 16/27: compiler_builtins                                                                                                           
  --> rustc/compiler_builtins_shim/../../libcompiler_builtins/src/probestack.rs:55:5
   |
55 | /     asm!("
56 | |         mov    %rax,%r11        // duplicate %rax as we're clobbering %r11
57 | |
58 | |         // Main loop, taken in one page increments. We're decrementing rsp by
...  |
92 | |         ret
93 | |     " ::: "memory" : "volatile");
   | |_________________________________^

error: aborting due to previous error

I'm on macOS 10.12.6. This error was added recently (#54568), but it suggests there's been a problem for longer.

[varkor]

And here:

error[E0668]: malformed inline assembly============================>   ] 26/27: std                                                                                                                         
  --> ~/GitHub/rust/src/libcore/../stdsimd/coresimd/x86/cpuid.rs:64:9
   |
64 | /         asm!("cpuid\n"
65 | |              : "={eax}"(r.eax), "={ebx}"(r.ebx), "={ecx}"(r.ecx), "={edx}"(r.edx)
66 | |              : "{eax}"(leaf), "{ecx}"(sub_leaf)
67 | |              : "rbx" :);
   | |________________________^

error[E0668]: malformed inline assembly
  --> ~/GitHub/rust/src/libcore/../stdsimd/coresimd/x86/xsave.rs:91:5
   |
91 |     asm!("xgetbv" : "={eax}"(eax), "={edx}"(edx) : "{ecx}"(xcr_no));
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 2 previous errors

[dsciarra]

OK on macOS 10.14

[levex]

Hmm, I added that error code, and I find that pretty odd. Sadly, I am unable to reproduce this on Linux and I don’t have access to a macOS machine right now.

The error code is emitted if we pass the inline assembly (with its constraints) to LLVM and for some reason it rejects it. (that is, the function InlineAsm::Verify returns false in src/llvm/lib/IR/InlineAsm.cpp. If you have access to the rust source code (which you do since you are trying to get it to compile :p ), it would be appreciated if added a few printfs around the return false; statements in the above mentioned file. That way, we could pinpoint why LLVM rejected these seemingly valid inline assembly statements.

Thanks!

[varkor]

Okay, this is strange. InlineAsm::Verify is returning true and yet the malformed assembly message is still being output. I've found the problem, but not what's causing it:

rust/src/librustc_codegen_llvm/builder.rs

Lines 757 to 758 in 5ea8eb5

	let constraints_ok = llvm::LLVMRustInlineAsmVerify(fty, cons);
	debug!("Constraint verification result: {:?}", constraints_ok);

constraints_ok is 769 here.