Given that the previous design would require the use of a default
allocator to have `ArgIterator.init()` work in WASI, and since in
Zig we're trying to avoid default allocators, I've changed the design
slightly in that now `init()` is a compile error in WASI, and instead
in its message it points to `initWithAllocator(*mem.Allocator)`.
The latter by virtue of requiring an allocator as an argument can
safely be used in WASI as well as on other OSes (where the allocator
argument is simply unused). When using `initWithAllocator` it is then
natural to remember to call `deinit()` after being done with the
iterator. Also, to make use of this, I've also added `argsWithAllocator`
function which is equivalent to `args` minus the requirement of supplying
an allocator and being fallible.
Finally, I've also modified the WASI only test `process.ArgWasiIterator`
to test all OSes.
This commit pulls WASI specific implementation of args extraction
from the runtime from `process.argsAlloc` and `process.argsFree`
into a new iterator struct `process.ArgIteratorWasi`. It also
integrates the struct with platform-independent `process.ArgIterator`.
* Deleted decls are deleted; unused decls are also detected as deleted.
Cycles are not yet detected.
* Re-analysis is smarter and will not cause a re-analysis of dependants
when only a function body is changed.
The binary file abstraction changed its struct named "Decl" to
"TextBlock" and it now represents an allocated slice of memory in
the .text section. It has two new fields: prev and next, making it
a linked list node. This allows a TextBlock to find its neighbors.
The ElfFile struct now has free_list and last_text_block fields.
Doc comments for free_list are reproduced here:
A list of text blocks that have surplus capacity. This list can have false
positives, as functions grow and shrink over time, only sometimes being added
or removed from the freelist.
A text block has surplus capacity when its overcapacity value is greater than
minimum_text_block_size * alloc_num / alloc_den. That is, when it has so
much extra capacity, that we could fit a small new symbol in it, itself with
ideal_capacity or more.
Ideal capacity is defined by size * alloc_num / alloc_den.
Overcapacity is measured by actual_capacity - ideal_capacity. Note that
overcapacity can be negative. A simple way to have negative overcapacity is to
allocate a fresh text block, which will have ideal capacity, and then grow it
by 1 byte. It will then have -1 overcapacity.
The last_text_block keeps track of the end of the .text section.
Allocation, freeing, and resizing decls are all now more sophisticated,
and participate in the virtual address allocation scheme. There is no
longer the possibility for virtual address collisions.
I'm not sure why I disabled them when landing extended Wasm/WASI
support, but they pass the parser tests just fine now, so I'm gonna
go ahead and re-enable them.
