SysV.cpp

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#include "Common.h"
#include "CothreadPrivate.h"
 
#include "SysV.S"
 
#include <cstddef>
#include <stdexcept>
 
using namespace libcommunism;
using namespace libcommunism::internal;
 
const size_t Amd64::kNumSavedRegisters{6};
 
void Amd64::ValidateStackSize(const size_t size) {
    if(!size) throw std::runtime_error("Size may not be nil");
    if(size % kStackAlignment) throw std::runtime_error("Stack is misaligned");
}
 
void* Amd64::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 Amd64::DeallocStack(void* stack) {
    free(stack);
}
 
void Amd64::Prepare(Amd64 *wrap, const Entry &entry) {
    static_assert(offsetof(Amd64, 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");
 
    // NOLINTBEGIN(cppcoreguidelines-pro-type-reinterpret-cast)
    // prepare some space for a stack frame (zeroed registers; four function call params)
    auto &stackBuf = wrap->stack;
    auto stackFrame = reinterpret_cast<std::byte *>(stackBuf.data());
    stackFrame += ((stackBuf.size()*sizeof(typeof(*stackBuf.data()))) & ~(0x10-1))
        - (sizeof(uintptr_t) * (4 + kNumSavedRegisters));
    auto stack = reinterpret_cast<uintptr_t *>(stackFrame);
 
    // method to execute if main method returns
    *--stack = reinterpret_cast<uintptr_t>(&Amd64::EntryReturnedStub);
 
    // and then jump to the stub that calls the entry point
    *--stack = reinterpret_cast<uintptr_t>(info);
    *--stack = reinterpret_cast<uintptr_t>(&Amd64::DereferenceCallInfo);
    *--stack = reinterpret_cast<uintptr_t>(&Amd64::JumpToEntry);
    // NOLINTEND(cppcoreguidelines-pro-type-reinterpret-cast)
 
    // clear the region that registers are written into (so they're all zeroed)
    for(size_t i = 0; i < kNumSavedRegisters; i++) {
        *--stack = 0;
    }
 
    // restore the stack pointer to the correct point
    wrap->stackTop = stack;
}