WebAssembly/Roadmap

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Short-Term

These steps are critical for completion in order to have wasm a full scope CPU target for FPC compiler

Feature Status Description
Assembly (textual wasm) working Pick an assembler utility that's sequence instruction (FPC) friendly

FPC should produce a textual assembly file.

Currently, FPC uses the LLVM assembler llvm-mc.

Linking working Pick an linker utility that's sequence instruction (FPC) friendly.

Linker is a moving target. As a new feature is added, the linking needs to be re-verified.

Currently, FPC uses the LLVM linker.

Basic function calls and local variables working Implement direct function calls, with passing basic parameters (that don't require any memory. I.e. int and floats)
Verify float-point values working As the float points are being converted from the textual format. It's necessary to make sure that the proper values are generated. As of now, they appear to work, including + or - infinity and NaNs. NaN with payload is not supported yet, see long term goals.
Global variables working Implement symbol reference to global variables (basic or complex)

Consider linking - as the index of symbols can change. (Wasm binaries are index based )

Stack/Call frame support working WebAssembly doesn't have any native stack and/or frame support.

It has to be emulated using global and local variables.

Blocking issue: https://github.com/WebAssembly/wabt/issues/1199

Indirect function calls working WebAssembly has a specific way of indirect calls

Needed for vmt and procedure variables (callback) calls

VMT working Support for calls via virtual method table
RTL.Memory Manager working
RTL.(Ansi/Wide) String Manager working
RTL.WASI.Console I/O working Standard input, standard output and error output (stderr) works on the WASI target.
RTL.WASI.Command line parameters working Both ParamStr and ParamCount work.
RTL.WASI.Exit codes working Terminating the program with an exit code via halt(XXX) works.
RTL.WASI.Randomize working Works.
RTL.WASI.File I/O in progress The WASI target needs a mechanism for converting path names (both relative and absolute) to paths, relative to a given set of preopened directories (these are the directories you're given access to). Also, the concept of current directory needs to be emulated, too. This is partially implemented now, although changing the current directory is not yet implemented.

Relevant upstream development to follow: [1]

RTL.WASI.File I/O.Basic File I/O working This covers basic sequential reading and writing of text and binary files. This includes Assign, Reset, Rewrite, Append, Close, Read, Write, Readln, Writeln, EoF, EoLn, BlockRead, BlockWrite. Working.
RTL.WASI.File I/O.ChDir not implemented Not yet implemented.
RTL.WASI.File I/O.MkDir working Creating a directory works.
RTL.WASI.File I/O.RmDir working Deleting an empty directory works.
RTL.WASI.File I/O.GetDir working Getting the current directory is emulated.
RTL.WASI.File I/O.Erase working Deleting a file works.
RTL.WASI.File I/O.Rename working Renaming a file works.
RTL.WASI.File I/O.Seek working Seeking inside an open file works.
RTL.WASI.File I/O.FileSize working Getting the size of a file works.
RTL.WASI.File I/O.FilePos working Getting the current position in a file works.
RTL.WASI.File I/O.Truncate working Truncating a file works.
RTL.WASI.DOS.FindFirst/FindNext/FindClose working Working.
RTL.WASI.DOS.Environment variables working This includes the environment variables of the DOS unit: GetEnv, EnvCount, EnvStr.
RTL.WASI.DOS.GetDate/GetTime working Works, but returns UTC time, instead of local time, because WASI lacks timezone support.
RTL.WASI.DOS.SetDate/SetTime not implemented Not yet implemented.
RTL.WASI.DOS.GetMsCount not implemented Not yet implemented.
RTL.WASI.DOS.GetFTime working Works, but returns UTC time, instead of local time, because WASI lacks timezone support.
RTL.WASI.DOS.SetFTime not implemented Not yet implemented.
RTL.WASI.DOS.GetFAttr not implemented Not yet implemented.
RTL.WASI.DOS.SetFAttr not implemented Not yet implemented.
RTL.WASI.DOS.FSearch not implemented Not yet implemented.
RTL.WASI.DOS.DiskFree not implemented Not sure if possible to implemented in WASI.
RTL.WASI.DOS.DiskSize not implemented Not sure if possible to implemented in WASI.
RTL.WASI.SysUtils unit in progress Unit compiles, but is untested. The file operations are not yet implemented.
RTL.WASI.Classes unit working Compiles and appears to be working. Needs more testing. Enabling one of exception handling modes is highly recommended.

Long-Term

Future improvements for wasm target. Some of those are nice to have, but not critical. Others are difficult to implement or need features of WebAssembly, which haven't been standardized yet.

Feature Status Description
Debug Info in progress There's experimental DWARF support for WebAssembly, but it isn't working yet and the debugging tools for WebAssembly aren't very mature at this point even for C and C++.

There's an LLVM linker bug, related to generating linker map files: [2]

Internal Object Writer working Enabled by default in commit bc76487b878e59133ce3c2cc19ebb13f9a9826ea
Internal Linker not implemented
GOTO support not implemented Goto is difficult to implement, due to WebAssembly's lack of labels and jumps. It requires all gotos to be converted to structured flow, such as loops and break/continue. This requires implementing a complex algorithm, such as Relooper or Stackifier. Useful read: [3]
Exceptions support (no exceptions mode) working By default, exceptions are disabled. However, try..finally blocks still work and execute their finally section, even when using the 'exit', 'break' or 'continue' statements. Try..except blocks are compiled, however the 'except' part is never executed. And invoking 'raise' terminates the program, since exceptions cannot be caught in this mode.
Exceptions support (native exceptions mode) working Requires the exception handling proposal: [4] Information about the browser support for this new experimental feature is available here: [5]
Exceptions support (branchful exceptions mode) working This is a compatibility mode, that implements exception support by adding branching after each function call. This incurs a large runtime cost, but is compatible with all WebAssembly implementations and doesn't require the WebAssembly implementation to be JavaScript hosted. This is the only approach, that currently works with wasmtime.
Exceptions support (JavaScript-based exceptions handling mode) not implemented This is the compatibility mode, used by Emscripten. This also incurs a runtime cost, and also requires the WebAssembly implementation to be JavaScript-based, so this is not supported by wasmtime. In this mode, each function call inside a try block is wrapped inside a JavaScript function call, that wraps the WebAssembly function in a try .. catch JavaScript statement block.
Timezone support not implemented WASI currently lacks timezone support. This also applies to WASI's C library in the official SDK. It is possible to parse the TZ environment variable, and read the binary timezone data from the file system, in case that is accessible, however this is probably not portable, and isn't done by their C library. Upstream bug reports: [6] [7] [8]
Multithreading support not implemented Threads are not supported in WebAssembly MVP. There is a future proposal here: [9] It is already implemented in most browsers: [10] However, it is not yet supported by WASI and wasmtime, so there's no spec or API for creating threads.
Process support - RTL.WASI.DOS.Exec/DosExitCode, fcl-process, etc. not implemented WASI does not support starting processes, yet. Proposal is here: [[11]]

See Also