On emscripten, function pointer casts can cause function call failure.
This commit fixes the function definition to match to the type of the
function call.

- qtest_set_command_cb passed to g_once should match to GThreadFunc
- object_class_cmp and cpreg_key_compare are passed to g_list_sort as
  GCopmareFunc but GLib cast them to GCompareDataFunc.

Signed-off-by: Kohei Tokunaga <[email protected]>

Signed-off-by: Kohei Tokunaga <[email protected]>

Signed-off-by: Kohei Tokunaga <[email protected]>

Emscripten does not support couroutine methods currently used by QEMU but
provides a coroutine implementation called "fiber". This commit introduces a
coroutine backend using fiber. Note that fiber does not support submitting
coroutines to other threads.

Signed-off-by: Kohei Tokunaga <[email protected]>

has_int128_type is set to false on emscripten as of now to avoid errors by
libffi. And tests aren't integrated with Wasm execution environment as of
now so this commit disables tests.

Signed-off-by: Kohei Tokunaga <[email protected]>

To enable 64-bit guest support in Wasm 32bit memory model today, it was
necessary to partially revert recent changes that removed support for
different pointer widths between the host and guest (e.g., commits
a70af12 and
bf455ec) when compiling with
Emscripten. While this serves as a temporary workaround, a long-term
solution could involve adopting Wasm's 64-bit memory model once it gains
broader support, as it is currently not widely adopted (e.g., unsupported by
Safari and libffi).

Signed-off-by: Kohei Tokunaga <[email protected]>

A TB consists of a wasmTBHeader followed by the data listed below. The
wasmTBHeader contains pointers for each element:

- TCI code
- Wasm code
- Array of function indices imported into the Wasm instance
- Counter tracking the number of TB executions
- Pointer to the Wasm instance information

The Wasm backend (tcg/wasm32.c) and Wasm instances running on the same
thread share information, such as CPUArchState, through a wasmContext
structure. The Wasm backend defines tcg_qemu_tb_exec as a common entry point
for TBs, similar to the TCI backend. tcg_qemu_tb_exec runs TBs on a forked
TCI interpreter by default, while compiles and executes frequently executed
TBs as Wasm.

The code generator (tcg/wasm32) receives TCG IR and generates both Wasm and
TCI instructions. Since Wasm cannot directly jump to specific addresses,
labels are implemented using Wasm control flow instructions. As shown in the
pseudo-code below, a TB wraps instructions in a large loop, where codes are
placed within if blocks separated by labels. Branching is handled by
breaking from the current block and entering the target block.

loop
  if
    ... code after label1
  end
  if
    ... code after label2
  end
  ...
end

Additionally, the Wasm backend differs from other backends in several ways:

- goto_tb and goto_ptr return control to tcg_qemu_tb_exec which runs the
  target TB
- Helper function pointers are stored in an array in TB and imported into
  the Wasm instance on execution
- Wasm TBs lack prologue and epilogue. TBs are executed via tcg_qemu_tb_exec

Browsers cause out of memory error if too many Wasm instances are
created. To prevent this, the Wasm backend tracks active instances using an
array. When instantiating a new instance risks exceeding the limit, the
backend removes older instances to avoid browser errors. These removed
instances are re-instantiated when needed.

Signed-off-by: Kohei Tokunaga <[email protected]>

Emscripten's fiber does not support submitting coroutines to other
threads. So this commit modifies hw/9pfs/coth.h to disable this behavior
when compiled with Emscripten.

Signed-off-by: Kohei Tokunaga <[email protected]>

Add GitLab CI job that builds QEMU using emscripten. The build runs in the
added Dockerfile that contains dependencies (glib, libffi, pixman, zlib)
compiled by emscripten.

Signed-off-by: Kohei Tokunaga <[email protected]>

Signed-off-by: Kohei Tokunaga <[email protected]>

Signed-off-by: Kohei Tokunaga <[email protected]>