Undefined reference to `Main_runtime_override_defaults_oo'

[presidentbeef]

I am just trying to get basic C linking working.

Upfront, this is the error:

/bin/ld: /home/justin/.local/share/ponyup/ponyc-release-0.33.2-x86_64-linux-gnu/lib/x86-64/libponyrt.a(start.o): in function `pony_init':
start.c:(.text+0x91): undefined reference to `Main_runtime_override_defaults_oo'
collect2: error: ld returned 1 exit status

Main_runtime_override_defaults_oo was added recently in 0.33.0 so I'm guessing it just isn't exposed correctly in libponyrt.a

I think this is easy for Pony developers to reproduce, but just in case I'm doing something wrong, here is what I did:

I have a tiny Pony file called try_pony.pony:

actor@ Try
  new create() =>
    None

I compile it with ponyc --library to get try_pony.h and libtry_pony.a.

Then I have a tiny C file called test.c:

#include <stdio.h>
#include "try_pony.h"
#include "pony.h"

int main(int argc, char** argv) { 
  pony_init(argc, argv);

  Try* x = Try_Alloc();
  Try_tag_create_o__send(x);

  pony_start(true, NULL, NULL);
  return 0;
}

Then I compile like this:

export PONYRT_INCLUDE=/home/justin/.local/share/ponyup/ponyc-release-0.33.2-x86_64-linux-gnu/include/
export PONYRT_LIB=/home/justin/.local/share/ponyup/ponyc-release-0.33.2-x86_64-linux-gnu/lib/x86-64/libponyrt.a

gcc -o test -I. -I $PONYRT_INCLUDE \
    -g -rdynamic -mcx16 test.c libtry_pony.a $PONYRT_LIB -lpthread -ldl -latomic

This results in the error above.

Now, if I do the dumbest thing possible and add this to my C file:

void Main_runtime_override_defaults_oo(void* opt)
{
  return;
}

Then it compiles fine.

[SeanTAllen]

After looking at this, I believe you are required to add the function yourself in your case at the moment.

@jemc do you concur based on looking at how it currently exists?

[jemc]

Yeah, based on how it currently exists, doing what OP called "the dumbest thing possible" is the correct way to get this to work. That is, adding a definition like this will make it work:

void Main_runtime_override_defaults_oo(void* opt)
{
  (void)opt; // avoid warning/error about unused variable
  return;
}

Currently, this works in Pony programs by the Pony compiler generating a default implementation of this method if the program had none:

ponyc/src/libponyc/pass/sugar.c

Lines 112 to 116 in b6265be

	// If have no @runtime_override_defaults method, add one.
	if(has_member(members, "runtime_override_defaults"))
	return;
	ast_append(members, make_runtime_override_defaults(ast));

For more general info about this feature, see https://github.com/ponylang/ponyc/blob/b6265be32d39b371a1b4b9f8dba8cf71c74fd578/packages/builtin/runtime_options.pony

Is this the cleanest way this feature could have been implemented? Maybe not, because it makes some assumptions about only using the Pony runtime with the ponyc compiler, and as we can see in this issue ticket, it inconveniences uses of Pony for generating C API functions.

It might be worth revisiting how this might be implemented in a cleaner way.

[presidentbeef]

Just want to point out that I didn't mean "the dumbest thing possible" in a derogatory way, I'm just not much of a C programmer so I don't know what makes sense.

Thanks!

[jemc]

Yeah, I didn't take it in a derogatory way - I just found it to be a funny situation and was glad to see that you got the workaround right on your first try.