Archipelago » qemu

/* Define to jump the ELF file used to communicate with GDB.  */

#undef DEBUG_JIT

#if TCG_TARGET_REG_BITS == 64

# define ELF_CLASS  ELFCLASS64

#else

# define ELF_CLASS  ELFCLASS32

#endif

#ifdef HOST_WORDS_BIGENDIAN

# define ELF_DATA   ELFDATA2MSB

#else

# define ELF_DATA   ELFDATA2LSB

#endif

static void tcg_register_jit_int(void *buf, size_t size,

                                 void *debug_frame, size_t debug_frame_size)

    __attribute__((unused));

#ifdef ELF_HOST_MACHINE

/* The backend should define ELF_HOST_MACHINE to indicate both what value to

   put into the ELF image and to indicate support for the feature.  */

/* Begin GDB interface.  THE FOLLOWING MUST MATCH GDB DOCS.  */

typedef enum {

    JIT_NOACTION = 0,

    JIT_REGISTER_FN,

    JIT_UNREGISTER_FN

} jit_actions_t;

struct jit_code_entry {

    struct jit_code_entry *next_entry;

    struct jit_code_entry *prev_entry;

    const void *symfile_addr;

    uint64_t symfile_size;

};

struct jit_descriptor {

    uint32_t version;

    uint32_t action_flag;

    struct jit_code_entry *relevant_entry;

    struct jit_code_entry *first_entry;

};

void __jit_debug_register_code(void) __attribute__((noinline));

void __jit_debug_register_code(void)

{

    asm("");

}

/* Must statically initialize the version, because GDB may check

   the version before we can set it.  */

struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };

/* End GDB interface.  */

static int find_string(const char *strtab, const char *str)

{

    const char *p = strtab + 1;

    while (1) {

        if (strcmp(p, str) == 0) {

            return p - strtab;

        }

        p += strlen(p) + 1;

    }

}

static void tcg_register_jit_int(void *buf, size_t buf_size,

                                 void *debug_frame, size_t debug_frame_size)

{

    static const char strings[64] =

        "\0"

        ".text\0"

        ".debug_frame\0"

        ".symtab\0"

        ".strtab\0"

        "code_gen_buffer";

    struct ElfImage {

        ElfW(Ehdr) ehdr;

        ElfW(Phdr) phdr;

        ElfW(Shdr) shdr[5];

        ElfW(Sym)  sym[1];

        char       str[64];

    };

    /* We only need a single jit entry; statically allocate it.  */

    static struct jit_code_entry one_entry;

    size_t img_size = sizeof(struct ElfImage) + debug_frame_size;

    struct ElfImage *img = g_malloc0(img_size);

    img->ehdr.e_ident[EI_MAG0] = ELFMAG0;

    img->ehdr.e_ident[EI_MAG1] = ELFMAG1;

    img->ehdr.e_ident[EI_MAG2] = ELFMAG2;

    img->ehdr.e_ident[EI_MAG3] = ELFMAG3;

    img->ehdr.e_ident[EI_CLASS] = ELF_CLASS;

    img->ehdr.e_ident[EI_DATA] = ELF_DATA;

    img->ehdr.e_ident[EI_VERSION] = EV_CURRENT;

    img->ehdr.e_type = ET_EXEC;

    img->ehdr.e_machine = ELF_HOST_MACHINE;

    img->ehdr.e_version = EV_CURRENT;

    img->ehdr.e_phoff = offsetof(struct ElfImage, phdr);

    img->ehdr.e_shoff = offsetof(struct ElfImage, shdr);

    img->ehdr.e_ehsize = sizeof(ElfW(Shdr));

    img->ehdr.e_phentsize = sizeof(ElfW(Phdr));

    img->ehdr.e_phnum = 1;

    img->ehdr.e_shentsize = sizeof(img->shdr[0]);

    img->ehdr.e_shnum = ARRAY_SIZE(img->shdr);

    img->ehdr.e_shstrndx = ARRAY_SIZE(img->shdr) - 1;

    img->phdr.p_type = PT_LOAD;

    img->phdr.p_offset = (char *)buf - (char *)img;

    img->phdr.p_vaddr = (ElfW(Addr))buf;

    img->phdr.p_paddr = img->phdr.p_vaddr;

    img->phdr.p_filesz = 0;

    img->phdr.p_memsz = buf_size;

    img->phdr.p_flags = PF_X;

    memcpy(img->str, strings, sizeof(img->str));

    img->shdr[0].sh_type = SHT_NULL;

    /* Trick: The contents of code_gen_buffer are not present in this fake

       ELF file; that got allocated elsewhere, discontiguously.  Therefore

       we mark .text as SHT_NOBITS (similar to .bss) so that readers will

       not look for contents.  We can record any address at will.  */

    img->shdr[1].sh_name = find_string(img->str, ".text");

    img->shdr[1].sh_type = SHT_NOBITS;

    img->shdr[1].sh_flags = SHF_EXECINSTR | SHF_ALLOC;

    img->shdr[1].sh_addr = (ElfW(Addr))buf;

    img->shdr[1].sh_size = buf_size;

    img->shdr[2].sh_name = find_string(img->str, ".debug_frame");

    img->shdr[2].sh_type = SHT_PROGBITS;

    img->shdr[2].sh_offset = sizeof(*img);

    img->shdr[2].sh_size = debug_frame_size;

    memcpy(img + 1, debug_frame, debug_frame_size);

    img->shdr[3].sh_name = find_string(img->str, ".symtab");

    img->shdr[3].sh_type = SHT_SYMTAB;

    img->shdr[3].sh_offset = offsetof(struct ElfImage, sym);

    img->shdr[3].sh_size = sizeof(img->sym);

    img->shdr[3].sh_info = ARRAY_SIZE(img->sym);

    img->shdr[3].sh_link = img->ehdr.e_shstrndx;

    img->shdr[3].sh_entsize = sizeof(ElfW(Sym));

    img->shdr[4].sh_name = find_string(img->str, ".strtab");

    img->shdr[4].sh_type = SHT_STRTAB;

    img->shdr[4].sh_offset = offsetof(struct ElfImage, str);

    img->shdr[4].sh_size = sizeof(img->str);

    img->sym[0].st_name = find_string(img->str, "code_gen_buffer");

    img->sym[0].st_info = ELF_ST_INFO(STB_GLOBAL, STT_FUNC);

    img->sym[0].st_shndx = 1;

    img->sym[0].st_value = (ElfW(Addr))buf;

    img->sym[0].st_size = buf_size;

#ifdef DEBUG_JIT

    /* Enable this block to be able to debug the ELF image file creation.

       One can use readelf, objdump, or other inspection utilities.  */

    {

        FILE *f = fopen("/tmp/qemu.jit", "w+b");

        if (f) {

            if (fwrite(img, img_size, 1, f) != buf_size) {

                /* Avoid stupid unused return value warning for fwrite.  */

            }

            fclose(f);

        }

    }

#endif

    one_entry.symfile_addr = img;

    one_entry.symfile_size = img_size;

    __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;

    __jit_debug_descriptor.relevant_entry = &one_entry;

    __jit_debug_descriptor.first_entry = &one_entry;

    __jit_debug_register_code();

}

#else

/* No support for the feature.  Provide the entry point expected by exec.c.  */

static void tcg_register_jit_int(void *buf, size_t size,

                                 void *debug_frame, size_t debug_frame_size)

{

}

void tcg_register_jit(void *buf, size_t buf_size)

{

}

#endif /* ELF_HOST_MACHINE */