AAPCS.cpp

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#include "Common.h"
#include "CothreadPrivate.h"
 
#include "AAPCS.S"
 
#include <cstddef>
#include <stdexcept>
 
using namespace libcommunism;
using namespace libcommunism::internal;
 
extern "C" void Aarch64AapcsEntryStub();
 
void *Aarch64::AllocStack(const size_t bytes) {
    void* buf{ nullptr };
    int err{ -1 };
 
    err = posix_memalign(&buf, kStackAlignment, bytes);
    if (err) {
        throw std::runtime_error("posix_memalign() failed");
    }
 
    return buf;
}
 
void Aarch64::DeallocStack(void* stack) {
    free(stack);
}
 
void Aarch64::Prepare(Aarch64 *thread, const Entry &entry) {
    static_assert(offsetof(Aarch64, stackTop) == COTHREAD_OFF_CONTEXT_TOP, "cothread stack top is invalid");
 
    // build the context structure we pass to our "fake" entry point
    auto info = new CallInfo{entry};
    if(!info) throw std::runtime_error("Failed to allocate call info");
 
    // build up the stack frame
    auto &stack = thread->stack;
    const auto stackBottom = reinterpret_cast<uintptr_t>(stack.data()) +
        (stack.size() * sizeof(uintptr_t));
    auto context = reinterpret_cast<uintptr_t *>(stack.data());
 
    context[0]  = stackBottom; // sp
    context[1]  = reinterpret_cast<uintptr_t>(Aarch64AapcsEntryStub); // x30/lr
    context[2]  = reinterpret_cast<uintptr_t>(info); // x19
    context[12] = stackBottom; //x29/fp
 
    // we use the `stackTop` ptr to point to the context area
    thread->stackTop = context;
}