[llvm] r293936 - Change how we handle section symbols on ELF.

[Rafael Avila de Espindola via llvm-commits]

Mikael Holmén <mikael.holmen at ericsson.com> writes:

> Hi Rafael,
>
> I have a question about this change.
...
>> This patch includes a few hacks to avoid changing our behaviour when
>> handling conflicts between section symbols and other symbols. I
>> reported pr31850 to track that.
>
> For my out-of-tree backend, we output all code in a section called 
> exactly "code". With your patch we now run into the below problem if we 
> then also have a function called "code".
>
> For foo.ll:
>
> define void @code() {
>    ret void
> }
>
> If I do
>
> build/bin/llc -O0 -mtriple phoenix foo.ll -o -
>
> we get
>
>          .section code
> __FILE_START:
>          .global code
> llc: ../lib/MC/MCAsmStreamer.cpp:440: virtual void (anonymous 
> namespace)::MCAsmStreamer::EmitLabel(llvm::MCSymbol *): Assertion 
> `Symbol->isUndefined() && "Cannot define a symbol twice!"' failed.
>
> So now we seem to get a clash between the section and function names, 
> and the assertion fails.
>
> I suppose this was not intended or are we doing something stupid in our 
> backend?

It was not the intention to change it. What is line 440 for you?
Upstream it is just an empty line.

I tried to reproduce the problem with

define void @".text"() {
  ret void
}

but that doesn't crash and the function symbol takes precedence over the
text one.

Cheers,
Rafael