These steps are critical for completion in order to have wasm a full scope CPU target for FPC compiler
|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.|
|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.(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.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: 
|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.|
|RTL.WASI.File I/O.ChDir||not implemented||Not yet implemented.|
|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.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.SysUtils unit||in progress||Unit compiles, but is untested. The file operations are not yet implemented.|
|RTL.WASI.SysUtils.Platform independent utilities||working||This includes various string and pchar utilities, type helpers, conversion routines (e.g. Format, Trim, IntToStr, StrToInt, ...), generic (not related to the system clock) utilities (e.g. IsLeapYear), etc.|
|RTL.WASI.SysUtils.File I/O||not implemented|
|RTL.WASI.SysUtils.Environment variables||not implemented|
|RTL.WASI.SysUtils.Date and time functions, related to the system clock||not implemented|
|RTL.WASI.Classes unit||working||Compiles and appears to be working. Needs more testing. Enabling one of exception handling modes is highly recommended.|
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.
|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: 
|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: |
|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:  Information about the browser support for this new experimental feature is available here: |
|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:   |
|Multithreading support||not implemented||Threads are not supported in WebAssembly MVP. There is a future proposal here:  It is already implemented in most browsers:  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: []|
|RTL.WASI.DOS.DiskFree||not implemented||Not sure if supported by the WASI API. Can be implemented, if an appropriate WASI API is added in the future.|
|RTL.WASI.DOS.SetDate/SetTime||not implemented||Setting the system clock is not supported by the WASI API. Can be implemented, if an appropriate WASI API is added in the future.|