stage2: wasm-linker - Place decls in the correct segment and order segments

[Luukdegram]

Previously, all decls would be placed within the 'rodata' segment regardless of constness. With this change, we correctly put them into segments such as 'data' and 'bss'. The linker now also orders the segments in such a way to always place the bss segment last, which allows us to completely omit this segment in the case where the memory is exported and not imported from the runtime. This allows smaller binaries as the runtime itself will zero-initialize the memory for us.

[kubkon]

Previously, all decls would be placed within the 'rodata' segment regardless of constness. With this change, we correctly put them into segments such as 'data' and 'bss'. The linker now also orders the segments in such a way to always place the bss segment last, which allows us to completely omit this segment in the case where the memory is exported and not imported from the runtime. This allows smaller binaries as the runtime itself will zero-initialize the memory for us.

Do you overwrite the entire file on every flush per incremental update? If not, ensuring correct order for segments may require selectively moving segments in file (via copyRangeAll or related) if a Decl grows over the segment's size, etc. But if you wipe the entire file and write to it from scratch on every flush, this is obviously not an issue :-) I'm asking since this is what I have to deal with with MachO and to some extend Elf (as far as .bss and TLS will go).

[Luukdegram]

Do you overwrite the entire file on every flush per incremental update? If not, ensuring correct order for segments may require selectively moving segments in file (via copyRangeAll or related) if a Decl grows over the segment's size, etc. But if you wipe the entire file and write to it from scratch on every flush, this is obviously not an issue :-) I'm asking since this is what I have to deal with with MachO and to some extend Elf (as far as .bss and TLS will go).

The entire file indeed gets overwritten in its entirety during flush.

[kubkon]

Do you overwrite the entire file on every flush per incremental update? If not, ensuring correct order for segments may require selectively moving segments in file (via copyRangeAll or related) if a Decl grows over the segment's size, etc. But if you wipe the entire file and write to it from scratch on every flush, this is obviously not an issue :-) I'm asking since this is what I have to deal with with MachO and to some extend Elf (as far as .bss and TLS will go).

The entire file indeed gets overwritten in its entirety during flush.

Gotcha, thanks for clarifying!

[kubkon]

Awesome work!