• Enrico Bacis's avatar
    [wasm] Introduce the WasmContext · 6cd7a5a7
    Enrico Bacis authored
    The WasmContext struct introduced in this CL is used to store the
    mem_size and mem_start address of the wasm memory. These variables can
    be accessed at C++ level at graph build time (e.g., initialized during
    instance building). When the GrowMemory runtime is invoked, the context
    variables can be changed in the WasmContext at C++ level so that the
    generated code will load the correct values.
    
    This requires to insert a relocatable pointer only in the
    JSToWasmWrapper (and in the other wasm entry points), the value is then
    passed from function to function as an automatically added additional
    parameter. The WasmContext is then dropped when creating an Interpreter
    Entry or when invoking a JavaScript function. This removes the need of
    patching the generated code at runtime (i.e., when the memory grows)
    with respect to WASM_MEMORY_REFERENCE and WASM_MEMORY_SIZE_REFERENCE.
    However, we still need to patch the code at instance build time to patch
    the JSToWasmWrappers; in fact the address of the WasmContext is not
    known during compilation, but only when the instance is built.
    
    The WasmContext address is passed as the first parameter. This has the
    advantage of not having to move the WasmContext around if the function
    does not use many registers. This CL also changes the wasm calling
    convention so that the first parameter register is different from the
    return value register. The WasmContext is attached to every
    WasmMemoryObject, to share the same context with multiple instances
    sharing the same memory. Moreover, the nodes representing the
    WasmContext variables are cached in the SSA environment, similarly to
    other local variables that might change during execution.  The nodes are
    created when initializing the SSA environment and refreshed every time a
    grow_memory or a function call happens, so that we are sure that they
    always represent the correct mem_size and mem_start variables.
    
    This CL also removes the WasmMemorySize runtime (since it's now possible
    to directly retrieve mem_size from the context) and simplifies the
    GrowMemory runtime (since every instance now has a memory_object).
    
    R=ahaas@chromium.org,clemensh@chromium.org
    CC=gdeepti@chromium.org
    
    Change-Id: I3f058e641284f5a1bbbfc35a64c88da6ff08e240
    Reviewed-on: https://chromium-review.googlesource.com/671008
    Commit-Queue: Enrico Bacis <enricobacis@google.com>
    Reviewed-by: 's avatarClemens Hammacher <clemensh@chromium.org>
    Reviewed-by: 's avatarAndreas Haas <ahaas@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#48209}
    6cd7a5a7
wasm-run-utils.h 16.6 KB