Function buildPrologue

src/e9patch/e9trampoline.cpp:296–340

* Build a trampoline prologue, which may include instructions before the * patched instruction. The trampoline prologue allows other instructions * to jump to the trampoline "early", without having to go back to the main * program. The code is similar to buildBreak(). */

 * program.  The code is similar to buildBreak().
 */
static int buildPrologue(const Binary *B, const Instr *I,
    intptr_t addr, BuildMode mode = BUILD_SIZE, Buffer *buf = nullptr)
{
    if (!option_Opeephole)
        return 0;
    const Instr *J = getTrampolinePrologueStart(B->Es, I);
    if (J == nullptr || J == I)
        return 0;

    int r = 0;
    unsigned start = (mode == BUILD_BYTES? buf->size(): 0);
    std::vector<std::pair<const Instr *, intptr_t>> entries;
    for (; J != I; J = J->next())
    {
        int len = 0;
        switch (mode)
        {
            case BUILD_SIZE:
                len = relocateInstr(J, INTPTR_MIN);
                break;
            case BUILD_BYTES:
            {
                uint8_t *bytes = buf->bytes();
                intptr_t entry = addr;
                len = relocateInstr(J, addr, buf);
                if (len < 0)
                {
                    buf->reset(start);
                    break;
                }
                saveJump(B, entry, bytes, len);
                entries.push_back({J, entry});
            }
        }
        if (len < 0)
            return 0;
        addr += len;
        r += len;
    }

    for (const auto &entry: entries)
        setTrampolineEntry(B->Es, entry.first, entry.second);

    return r;
}

/*
 * Calculate trampoline size.