Hi Ken,
On Thu, Mar 14, 2019 at 2:09 PM ken.dickey@whidbey.com wrote:
Greetings,
I have been making small progress in getting Pharo's FFI unit tests to pass on arm64.
Built from recent OpenSmalltalk opensmalltalk-vm build.linux64ARMv8/pharo.stack.spur
I get a pharo vm whose UI is pretty slow (no JIT so far), so current progress is slow.
I am looking at #FFICallbackThunk>initializeARM32 but I don't yet understand quite what this code is trying to do, so have not made proper changes for arm64.
Anybody care to join in or advise me on this?
Note that I am neither a Pharo nor a UnifiedFFI user, so I may be making really dumb mistakes at this point (i.e. _you_ could help me out here! 8^).
Can we start from the last section of the comment for which I wrote on February 6th? I wrote the following. What is missing from this information that you need to understand how to proceed?
Callbacks are not handled by this plugin. Instead they are handled by image-level code to create Alien "thunks", small sequences of machine code, that invoke a function thunkEntry, implemented as required by each platform in one of the files in platforms/Cross/plugins/IA32ABI (a regrettable name; it should be something like platforms/Cross/plugins/AlienCallbacks). Each platform's thunkEntry has a signature that takes all integer register parameters (if any), all floating-point register parameters (if any), a pointer to the thunk, and the stack pointer at the point the thunk was invoiked. To pass a callback to foreign code, the marshaller in this plugin passes the address of the thunk. When external code calls that address the think is invoked, and it invokes thunkEntry as required. thunkEntry then saves its parameters locally in an instance of VMCallbackContext, which includes a jmpbuf. thunkEntry then does a setjmp and enters the VM via sendInvokeCallbackContext[:], which creates an activation of invokeCallbackContext: to execute the callback. This method then extracts the address of the thunk from the VMCallbackContext and invokes machinery in Callback to match the address with a Smalltalk block. The block is then evaluated with the parameters extracted from the VMCallbackContext, marshalled by methods in Callback subclasses signatures protocol, which know whether a parameter would be passed in a register or on the stack. The result of the block is then passed back to thunkEntry by storing it in a field in the VMCallbackContext and invoking primSignal:andReturnAs:fromContext:, which uses longjmp to jump back to thunkEntry which then extracts the result from its VMCallbackContext and returns.
For example, the signature of thunkEntry on x86/IA32 (platforms/Cross/plugins/IA32ABI/ia32abicc.c) is long thunkEntry(void *thunkp, sqIntptr_t *stackp) whereas on ARMv4/5/6 (platforms/Cross/plugins/IA32ABI/arm32abicc.c) it is long long thunkEntry(long r0, long r1, long r2, long r3, double d0, double d1, double d2, double d3, double d4, double d5, double d6, double d7, void *thunkpPlus16, sqIntptr_t *stackp)
Thanks much in advance, -KenD
_,,,^..^,,,_ best, Eliot