Please compress and attach the files mentioned here so we can easily reproduce the crash:

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
c++: note: diagnostic msg: /tmp/as_callfunc_x86-315a7c.cpp
c++: note: diagnostic msg: /tmp/as_callfunc_x86-315a7c.sh

(In reply to Nathan Owens from comment #0)
...
> fatal error: error in backend: No open frame
> c++: error: clang frontend command failed with exit code 70 (use -v to see
> invocation)
> FreeBSD clang version 3.4.1 (tags/RELEASE_34/dot1-final 208032) 20140512

The bug report title says "clang 6.0.0", but the crash message says clang 3.4.1 (which is the default compiler in FreeBSD 10.x).  It's not very likely that bugs in this old version will be fixed, but you should always save and attach the generated .cpp and .sh files.

(In reply to Dimitry Andric from comment #2)
> (In reply to Nathan Owens from comment #0)
> ...
> > fatal error: error in backend: No open frame
> > c++: error: clang frontend command failed with exit code 70 (use -v to see
> > invocation)
> > FreeBSD clang version 3.4.1 (tags/RELEASE_34/dot1-final 208032) 20140512
> 
> The bug report title says "clang 6.0.0", but the crash message says clang
> 3.4.1 (which is the default compiler in FreeBSD 10.x).  It's not very likely
> that bugs in this old version will be fixed, but you should always save and
> attach the generated .cpp and .sh files.

Yeah sorry, I forgot I got that error from freebsd 10.4, also having issues with 11.2 clang-6; Will attach both, except 11.2 doesn't generate those error reports like 10.4 did

Created attachment 20753 [details]
10.4 Files

Created attachment 20754 [details]
11.2 build log; Clang 6

This particular crash is an older issue, which has been "solved" in the mean time, by making it a non-fatal error.  After https://reviews.llvm.org/rL315264 ("[MC] Properly diagnose badly scoped .cfi_ directives"), it now prints:

error: this directive must appear between .cfi_startproc and .cfi_endproc directives

The problem is that angelscript is attempting some sort of workaround for optimizations messing up its assumptions about stack layout, e.g. it has this:

        asm __volatile__(
#ifdef __OPTIMIZE__
                // When compiled with optimizations the stack unwind doesn't work properly,
                // causing exceptions to crash the application. By adding this prologue
                // and the epilogue below, the stack unwind works as it should.
                // TODO: runtime optimize: The prologue/epilogue shouldn't be needed if the correct cfi directives are used below
                "pushl %%ebp               \n"
                ".cfi_adjust_cfa_offset 4  \n"
                ".cfi_rel_offset ebp, 0    \n"
                "movl %%esp, %%ebp         \n"
                ".cfi_def_cfa_register ebp \n"
#endif
                _S(CLEAR_FPU_STACK)    "\n"
                "pushl %%ebx            \n"
                "movl  %%edx, %%ebx     \n"

Before r315264, MCStreamer crashed with a "no open frame" error, if it encountered such 'naked' .cfi directives.  After r315264, it prints a regular error instead.

The easiest way to work around these errors is to change all the #ifdef __OPTIMIZE__ lines to:

#if defined(__OPTIMIZE__) && !defined(__clang__)

Btw, this is a very minimal test case:

$ cat pr38649.cpp
// clang -cc1 -triple i386-- -emit-obj pr38649.cpp
void a() { asm(".cfi_restore %ebp\n"); }

$ clang -cc1 -triple i386-- -emit-obj pr38649.cpp
error: this directive must appear between .cfi_startproc and .cfi_endproc directives
1 error generated.

If you attempt to compile this for x86_64, clang blows up in a different way:

$ clang -cc1 -triple x86_64-- -emit-obj -munwind-tables pr38649.cpp
Assertion failed: ((isUIntN(8 * Size, Value) || isIntN(8 * Size, Value)) && "Invalid size"), function EmitIntValue, file /usr/src/contrib/llvm/lib/MC/MCStreamer.cpp, line 115.
Abort trap

(In reply to Dimitry Andric from comment #7)
> Btw, this is a very minimal test case:
> 
> $ cat pr38649.cpp
> // clang -cc1 -triple i386-- -emit-obj pr38649.cpp
> void a() { asm(".cfi_restore %ebp\n"); }
> 
> $ clang -cc1 -triple i386-- -emit-obj pr38649.cpp
> error: this directive must appear between .cfi_startproc and .cfi_endproc
> directives
> 1 error generated.

This seems like everything is working as intended. If you want to do your own CFI, maybe use a standalone .s file or a naked function, or force -funwind-tables.

> If you attempt to compile this for x86_64, clang blows up in a different way:
> 
> $ clang -cc1 -triple x86_64-- -emit-obj -munwind-tables pr38649.cpp
> Assertion failed: ((isUIntN(8 * Size, Value) || isIntN(8 * Size, Value)) &&
> "Invalid size"), function EmitIntValue, file
> /usr/src/contrib/llvm/lib/MC/MCStreamer.cpp, line 115.
> Abort trap

That's lame. :( If you don't make an object, we generate this asm:

_Z1av:
        .cfi_startproc
        #APP
        .cfi_restore -2
        #NO_APP
        retq
        .cfi_endproc

The -2 comes from this line in X86RegisterInfo.td:
def EDI : X86Reg<"edi", 7, [DI, HDI]>, DwarfRegNum<[-2, 7, 7]>;
def EBP : X86Reg<"ebp", 5, [BP, HBP]>, DwarfRegNum<[-2, 4, 5]>;
def ESP : X86Reg<"esp", 4, [SP, HSP]>, DwarfRegNum<[-2, 5, 4]>;

The first entry is the register number used for 32-bit x86, and the second and third I don't know, maybe x64 and x32. I guess we need to diagnose it.