zig wasm linker lowers undefined and 0 incorrectly with respect to the bss section

Zig Version

0.11.0-dev.1898+36d47dd19

Steps to Reproduce and Observed Behavior

This test case is incorrect: https://github.com/ziglang/zig/blob/36d47dd1991f0ccd7a9673075624f09500cc415e/test/link/wasm/bss/build.zig

The global variable has value undefined: https://github.com/ziglang/zig/blob/36d47dd1991f0ccd7a9673075624f09500cc415e/test/link/wasm/bss/lib.zig#L1

So it should not go into the bss section in debug mode.

Furthermore, when I change the value to 0 it should definitely go into bss, however in this case the test fails.

Expected Behavior

Zig is technically allowed to lower undefined in any way it wants to, however the linker test can test the actual behavior of the linker. It should do the following for undefined:

Debug, ReleaseSafe: lower to 0xaa bytes
ReleaseFast, ReleaseSmall: lower to bss

For zero values, it must lower to bss.

cc @Luukdegram and @kubkon

Mar 07 '23 20:03 andrewrk

Thanks for reporting and clarifying this with me. I'll have a fix ready for both undefined and zero values this week :)

Mar 07 '23 21:03 Luukdegram

If you make it .build_modes = false and handle each of the build modes internally inside the build.zig file, that will make it easier for me to port the commit from master branch into #14647 :slightly_smiling_face:

Mar 07 '23 21:03 andrewrk