meson: hide all libc.so C++ symbols via a linker script

[ArsenArsen]

result: https://gist.github.com/ArsenArsen/570e87410c48f5b17f46d579269f10c2

btw, I noticed that we have a C++ function that probably should not be a C++ function:

0000000000068a58 T seed48(unsigned short*)
000000000008354a T login_tty(int)
000000000009f478 T wcstoimax(wchar_t const*, wchar_t**, int)
000000000009f4b7 T wcstoumax(wchar_t const*, wchar_t**, int)

this would imply we lack tests for those..

I recall some discussion about how to detect such cases before in the mlibc channel, but I do not recall the result. if you can find it/remember it, please share

[no92]

Detecting such errors might also be a convenient extra feature for a possible ABI checker.

[mintsuki]

LGTM

[ArsenArsen]

obviously the abi break is expected

[no92]

As is, this needs some changes; managarm uses __mlibc_getPassthrough in a few places, so this PR currently breaks boot.

[ArsenArsen]

that shouldn't break, since this only excludes _Z*? or am I missing something?

[qookei]

It's not marked extern "C" :^)

[ArsenArsen]

that's a silly name for a C++ function.. but, OK, we can export it also

[qookei]

Marking it extern "C" would be simpler, and I suppose more correct for a libc

[ArsenArsen]

and an abi break, which might be problematic depending on what it's used for

[Geertiebear]

Does that actually get used by other binaries?

[ArsenArsen]

I imagine boot wouldn't fail without it if it wasn't

[ArsenArsen]

based on the other __mlibc_ functions not being mangled I'm guessing that this is unintentionally not extern C. anyway, try this. might require that we start passing --no-undefined-version at some point

[ArsenArsen]

don't merge yet, need to add a dep to the link_deps of the .so

edit: done, pls test

[no92]

With managarm/managarm#715, the need to make __mlibc_getPassthrough be extern "C" is avoided. It no longer needs to be declared with C linkage or be excepted in the linker script.

[ArsenArsen]

okay, I'll revert that

[no92]

Works on my machine™