Python/jit.c

#ifdef _Py_JIT

#include "Python.h"

#include "pycore_abstract.h"
#include "pycore_call.h"
#include "pycore_ceval.h"
#include "pycore_dict.h"
#include "pycore_intrinsics.h"
#include "pycore_long.h"
#include "pycore_opcode_metadata.h"
#include "pycore_opcode_utils.h"
#include "pycore_optimizer.h"
#include "pycore_pyerrors.h"
#include "pycore_setobject.h"
#include "pycore_sliceobject.h"
#include "pycore_jit.h"

#include "jit_stencils.h"

// Memory management stuff: ////////////////////////////////////////////////////

#ifndef MS_WINDOWS
    #include <sys/mman.h>
#endif

static size_t
get_page_size(void)
{
#ifdef MS_WINDOWS
    SYSTEM_INFO si;
    GetSystemInfo(&si);
    return si.dwPageSize;
#else
    return sysconf(_SC_PAGESIZE);
#endif
}

static void
jit_error(const char *message)
{
#ifdef MS_WINDOWS
    int hint = GetLastError();
#else
    int hint = errno;
#endif
    PyErr_Format(PyExc_RuntimeWarning, "JIT %s (%d)", message, hint);
}

static char *
jit_alloc(size_t size)
{
    assert(size);
    assert(size % get_page_size() == 0);
#ifdef MS_WINDOWS
    int flags = MEM_COMMIT | MEM_RESERVE;
    char *memory = VirtualAlloc(NULL, size, flags, PAGE_READWRITE);
    int failed = memory == NULL;
#else
    int flags = MAP_ANONYMOUS | MAP_PRIVATE;
    char *memory = mmap(NULL, size, PROT_READ | PROT_WRITE, flags, -1, 0);
    int failed = memory == MAP_FAILED;
#endif
    if (failed) {
        jit_error("unable to allocate memory");
        return NULL;
    }
    return memory;
}

static int
jit_free(char *memory, size_t size)
{
    assert(size);
    assert(size % get_page_size() == 0);
#ifdef MS_WINDOWS
    int failed = !VirtualFree(memory, 0, MEM_RELEASE);
#else
    int failed = munmap(memory, size);
#endif
    if (failed) {
        jit_error("unable to free memory");
        return -1;
    }
    return 0;
}

static int
mark_executable(char *memory, size_t size)
{
    if (size == 0) {
        return 0;
    }
    assert(size % get_page_size() == 0);
    // Do NOT ever leave the memory writable! Also, don't forget to flush the
    // i-cache (I cannot begin to tell you how horrible that is to debug):
#ifdef MS_WINDOWS
    if (!FlushInstructionCache(GetCurrentProcess(), memory, size)) {
        jit_error("unable to flush instruction cache");
        return -1;
    }
    int old;
    int failed = !VirtualProtect(memory, size, PAGE_EXECUTE_READ, &old);
#else
    __builtin___clear_cache((char *)memory, (char *)memory + size);
    int failed = mprotect(memory, size, PROT_EXEC | PROT_READ);
#endif
    if (failed) {
        jit_error("unable to protect executable memory");
        return -1;
    }
    return 0;
}

static int
mark_readable(char *memory, size_t size)
{
    if (size == 0) {
        return 0;
    }
    assert(size % get_page_size() == 0);
#ifdef MS_WINDOWS
    DWORD old;
    int failed = !VirtualProtect(memory, size, PAGE_READONLY, &old);
#else
    int failed = mprotect(memory, size, PROT_READ);
#endif
    if (failed) {
        jit_error("unable to protect readable memory");
        return -1;
    }
    return 0;
}

// JIT compiler stuff: /////////////////////////////////////////////////////////

// Warning! AArch64 requires you to get your hands dirty. These are your gloves:

// value[value_start : value_start + len]
static uint32_t
get_bits(uint64_t value, uint8_t value_start, uint8_t width)
{
    assert(width <= 32);
    return (value >> value_start) & ((1ULL << width) - 1);
}

// *loc[loc_start : loc_start + width] = value[value_start : value_start + width]
static void
set_bits(uint32_t *loc, uint8_t loc_start, uint64_t value, uint8_t value_start,
         uint8_t width)
{
    assert(loc_start + width <= 32);
    // Clear the bits we're about to patch:
    *loc &= ~(((1ULL << width) - 1) << loc_start);
    assert(get_bits(*loc, loc_start, width) == 0);
    // Patch the bits:
    *loc |= get_bits(value, value_start, width) << loc_start;
    assert(get_bits(*loc, loc_start, width) == get_bits(value, value_start, width));
}

// See https://developer.arm.com/documentation/ddi0602/2023-09/Base-Instructions
// for instruction encodings:
#define IS_AARCH64_ADD_OR_SUB(I) (((I) & 0x11C00000) == 0x11000000)
#define IS_AARCH64_ADRP(I)       (((I) & 0x9F000000) == 0x90000000)
#define IS_AARCH64_BRANCH(I)     (((I) & 0x7C000000) == 0x14000000)
#define IS_AARCH64_LDR_OR_STR(I) (((I) & 0x3B000000) == 0x39000000)
#define IS_AARCH64_MOV(I)        (((I) & 0x9F800000) == 0x92800000)

// Fill all of stencil's holes in the memory pointed to by base, using the
// values in patches.
static void
patch(char *base, const Stencil *stencil, uint64_t *patches)
{
    for (uint64_t i = 0; i < stencil->holes_size; i++) {
        const Hole *hole = &stencil->holes[i];
        void *location = base + hole->offset;
        uint64_t value = patches[hole->value] + (uint64_t)hole->symbol + hole->addend;
        uint32_t *loc32 = (uint32_t *)location;
        uint64_t *loc64 = (uint64_t *)location;
        // LLD is a great reference for performing relocations... just keep in
        // mind that Tools/jit/build.py does filtering and preprocessing for us!
        // Here's a good place to start for each platform:
        // - aarch64-apple-darwin:
        //   - https://github.com/llvm/llvm-project/blob/main/lld/MachO/Arch/ARM64Common.cpp
        //   - https://github.com/llvm/llvm-project/blob/main/lld/MachO/Arch/ARM64Common.h
        // - aarch64-unknown-linux-gnu:
        //   - https://github.com/llvm/llvm-project/blob/main/lld/ELF/Arch/AArch64.cpp
        // - i686-pc-windows-msvc:
        //   - https://github.com/llvm/llvm-project/blob/main/lld/COFF/Chunks.cpp
        // - x86_64-apple-darwin:
        //   - https://github.com/llvm/llvm-project/blob/main/lld/MachO/Arch/X86_64.cpp
        // - x86_64-pc-windows-msvc:
        //   - https://github.com/llvm/llvm-project/blob/main/lld/COFF/Chunks.cpp
        // - x86_64-unknown-linux-gnu:
        //   - https://github.com/llvm/llvm-project/blob/main/lld/ELF/Arch/X86_64.cpp
        switch (hole->kind) {
            case HoleKind_IMAGE_REL_I386_DIR32:
                // 32-bit absolute address.
                // Check that we're not out of range of 32 unsigned bits:
                assert(value < (1ULL << 32));
                *loc32 = (uint32_t)value;
                continue;
            case HoleKind_ARM64_RELOC_UNSIGNED:
            case HoleKind_IMAGE_REL_AMD64_ADDR64:
            case HoleKind_R_AARCH64_ABS64:
            case HoleKind_X86_64_RELOC_UNSIGNED:
            case HoleKind_R_X86_64_64:
                // 64-bit absolute address.
                *loc64 = value;
                continue;
            case HoleKind_R_AARCH64_CALL26:
            case HoleKind_R_AARCH64_JUMP26:
                // 28-bit relative branch.
                assert(IS_AARCH64_BRANCH(*loc32));
                value -= (uint64_t)location;
                // Check that we're not out of range of 28 signed bits:
                assert((int64_t)value >= -(1 << 27));
                assert((int64_t)value < (1 << 27));
                // Since instructions are 4-byte aligned, only use 26 bits:
                assert(get_bits(value, 0, 2) == 0);
                set_bits(loc32, 0, value, 2, 26);
                continue;
            case HoleKind_R_AARCH64_MOVW_UABS_G0_NC:
                // 16-bit low part of an absolute address.
                assert(IS_AARCH64_MOV(*loc32));
                // Check the implicit shift (this is "part 0 of 3"):
                assert(get_bits(*loc32, 21, 2) == 0);
                set_bits(loc32, 5, value, 0, 16);
                continue;
            case HoleKind_R_AARCH64_MOVW_UABS_G1_NC:
                // 16-bit middle-low part of an absolute address.
                assert(IS_AARCH64_MOV(*loc32));
                // Check the implicit shift (this is "part 1 of 3"):
                assert(get_bits(*loc32, 21, 2) == 1);
                set_bits(loc32, 5, value, 16, 16);
                continue;
            case HoleKind_R_AARCH64_MOVW_UABS_G2_NC:
                // 16-bit middle-high part of an absolute address.
                assert(IS_AARCH64_MOV(*loc32));
                // Check the implicit shift (this is "part 2 of 3"):
                assert(get_bits(*loc32, 21, 2) == 2);
                set_bits(loc32, 5, value, 32, 16);
                continue;
            case HoleKind_R_AARCH64_MOVW_UABS_G3:
                // 16-bit high part of an absolute address.
                assert(IS_AARCH64_MOV(*loc32));
                // Check the implicit shift (this is "part 3 of 3"):
                assert(get_bits(*loc32, 21, 2) == 3);
                set_bits(loc32, 5, value, 48, 16);
                continue;
            case HoleKind_ARM64_RELOC_GOT_LOAD_PAGE21:
                // 21-bit count of pages between this page and an absolute address's
                // page... I know, I know, it's weird. Pairs nicely with
                // ARM64_RELOC_GOT_LOAD_PAGEOFF12 (below).
                assert(IS_AARCH64_ADRP(*loc32));
                // Number of pages between this page and the value's page:
                value = (value >> 12) - ((uint64_t)location >> 12);
                // Check that we're not out of range of 21 signed bits:
                assert((int64_t)value >= -(1 << 20));
                assert((int64_t)value < (1 << 20));
                // value[0:2] goes in loc[29:31]:
                set_bits(loc32, 29, value, 0, 2);
                // value[2:21] goes in loc[5:26]:
                set_bits(loc32, 5, value, 2, 19);
                continue;
            case HoleKind_ARM64_RELOC_GOT_LOAD_PAGEOFF12:
                // 12-bit low part of an absolute address. Pairs nicely with
                // ARM64_RELOC_GOT_LOAD_PAGE21 (above).
                assert(IS_AARCH64_LDR_OR_STR(*loc32) || IS_AARCH64_ADD_OR_SUB(*loc32));
                // There might be an implicit shift encoded in the instruction:
                uint8_t shift = 0;
                if (IS_AARCH64_LDR_OR_STR(*loc32)) {
                    shift = (uint8_t)get_bits(*loc32, 30, 2);
                    // If both of these are set, the shift is supposed to be 4.
                    // That's pretty weird, and it's never actually been observed...
                    assert(get_bits(*loc32, 23, 1) == 0 || get_bits(*loc32, 26, 1) == 0);
                }
                value = get_bits(value, 0, 12);
                assert(get_bits(value, 0, shift) == 0);
                set_bits(loc32, 10, value, shift, 12);
                continue;
        }
        Py_UNREACHABLE();
    }
}

static void
copy_and_patch(char *base, const Stencil *stencil, uint64_t *patches)
{
    memcpy(base, stencil->body, stencil->body_size);
    patch(base, stencil, patches);
}

static void
emit(const StencilGroup *group, uint64_t patches[])
{
    copy_and_patch((char *)patches[HoleValue_CODE], &group->code, patches);
    copy_and_patch((char *)patches[HoleValue_DATA], &group->data, patches);
}

// Compiles executor in-place. Don't forget to call _PyJIT_Free later!
int
_PyJIT_Compile(_PyExecutorObject *executor, _PyUOpInstruction *trace, size_t length)
{
    // Loop once to find the total compiled size:
    size_t code_size = 0;
    size_t data_size = 0;
    for (size_t i = 0; i < length; i++) {
        _PyUOpInstruction *instruction = &trace[i];
        const StencilGroup *group = &stencil_groups[instruction->opcode];
        code_size += group->code.body_size;
        data_size += group->data.body_size;
    }
    // Round up to the nearest page (code and data need separate pages):
    size_t page_size = get_page_size();
    assert((page_size & (page_size - 1)) == 0);
    code_size += page_size - (code_size & (page_size - 1));
    data_size += page_size - (data_size & (page_size - 1));
    char *memory = jit_alloc(code_size + data_size);
    if (memory == NULL) {
        return -1;
    }
    // Loop again to emit the code:
    char *code = memory;
    char *data = memory + code_size;
    for (size_t i = 0; i < length; i++) {
        _PyUOpInstruction *instruction = &trace[i];
        const StencilGroup *group = &stencil_groups[instruction->opcode];
        // Think of patches as a dictionary mapping HoleValue to uint64_t:
        uint64_t patches[] = GET_PATCHES();
        patches[HoleValue_CODE] = (uint64_t)code;
        patches[HoleValue_CONTINUE] = (uint64_t)code + group->code.body_size;
        patches[HoleValue_DATA] = (uint64_t)data;
        patches[HoleValue_EXECUTOR] = (uint64_t)executor;
        patches[HoleValue_OPARG] = instruction->oparg;
        patches[HoleValue_OPERAND] = instruction->operand;
        patches[HoleValue_TARGET] = instruction->target;
        patches[HoleValue_TOP] = (uint64_t)memory;
        patches[HoleValue_ZERO] = 0;
        emit(group, patches);
        code += group->code.body_size;
        data += group->data.body_size;
    }
    if (mark_executable(memory, code_size) ||
        mark_readable(memory + code_size, data_size))
    {
        jit_free(memory, code_size + data_size);
        return -1;
    }
    executor->jit_code = memory;
    executor->jit_size = code_size + data_size;
    return 0;
}

void
_PyJIT_Free(_PyExecutorObject *executor)
{
    char *memory = (char *)executor->jit_code;
    size_t size = executor->jit_size;
    if (memory) {
        executor->jit_code = NULL;
        executor->jit_size = 0;
        if (jit_free(memory, size)) {
            PyErr_WriteUnraisable(NULL);
        }
    }
}

#endif  // _Py_JIT