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Copyright (c) 2020, Andinus <andinus@nand.sh>

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

#ifdef TARGET_DEFS_ONLY

#define EM_TCC_TARGET EM_ARM

/* relocation type for 32 bit data relocation */
#define R_DATA_32   R_ARM_ABS32
#define R_DATA_PTR  R_ARM_ABS32
#define R_JMP_SLOT  R_ARM_JUMP_SLOT
#define R_GLOB_DAT  R_ARM_GLOB_DAT
#define R_COPY      R_ARM_COPY
#define R_RELATIVE  R_ARM_RELATIVE

#define R_NUM       R_ARM_NUM

#define ELF_START_ADDR 0x00008000
#define ELF_PAGE_SIZE  0x1000

#define PCRELATIVE_DLLPLT 1
#define RELOCATE_DLLPLT 0

enum float_abi {
    ARM_SOFTFP_FLOAT,
    ARM_HARD_FLOAT,
};

#else /* !TARGET_DEFS_ONLY */

#include "tcc.h"

/* Returns 1 for a code relocation, 0 for a data relocation. For unknown
   relocations, returns -1. */
int code_reloc (int reloc_type)
{
    switch (reloc_type) {
	case R_ARM_MOVT_ABS:
	case R_ARM_MOVW_ABS_NC:
	case R_ARM_THM_MOVT_ABS:
	case R_ARM_THM_MOVW_ABS_NC:
	case R_ARM_ABS32:
	case R_ARM_REL32:
	case R_ARM_GOTPC:
	case R_ARM_GOTOFF:
	case R_ARM_GOT32:
	case R_ARM_COPY:
	case R_ARM_GLOB_DAT:
	case R_ARM_NONE:
            return 0;

        case R_ARM_PC24:
        case R_ARM_CALL:
	case R_ARM_JUMP24:
	case R_ARM_PLT32:
	case R_ARM_THM_PC22:
	case R_ARM_THM_JUMP24:
	case R_ARM_PREL31:
	case R_ARM_V4BX:
	case R_ARM_JUMP_SLOT:
            return 1;
    }

    tcc_error ("Unknown relocation type: %d", reloc_type);
    return -1;
}

/* Returns an enumerator to describe whether and when the relocation needs a
   GOT and/or PLT entry to be created. See tcc.h for a description of the
   different values. */
int gotplt_entry_type (int reloc_type)
{
    switch (reloc_type) {
	case R_ARM_NONE:
	case R_ARM_COPY:
	case R_ARM_GLOB_DAT:
	case R_ARM_JUMP_SLOT:
            return NO_GOTPLT_ENTRY;

        case R_ARM_PC24:
        case R_ARM_CALL:
	case R_ARM_JUMP24:
	case R_ARM_PLT32:
	case R_ARM_THM_PC22:
	case R_ARM_THM_JUMP24:
	case R_ARM_MOVT_ABS:
	case R_ARM_MOVW_ABS_NC:
	case R_ARM_THM_MOVT_ABS:
	case R_ARM_THM_MOVW_ABS_NC:
	case R_ARM_PREL31:
	case R_ARM_ABS32:
	case R_ARM_REL32:
	case R_ARM_V4BX:
            return AUTO_GOTPLT_ENTRY;

	case R_ARM_GOTPC:
	case R_ARM_GOTOFF:
            return BUILD_GOT_ONLY;

	case R_ARM_GOT32:
            return ALWAYS_GOTPLT_ENTRY;
    }

    tcc_error ("Unknown relocation type: %d", reloc_type);
    return -1;
}

ST_FUNC unsigned create_plt_entry(TCCState *s1, unsigned got_offset, struct sym_attr *attr)
{
    Section *plt = s1->plt;
    uint8_t *p;
    unsigned plt_offset;

    /* when building a DLL, GOT entry accesses must be done relative to
       start of GOT (see x86_64 example above)  */
    if (s1->output_type == TCC_OUTPUT_DLL)
        tcc_error("DLLs unimplemented!");

    /* empty PLT: create PLT0 entry that push address of call site and
       jump to ld.so resolution routine (GOT + 8) */
    if (plt->data_offset == 0) {
        p = section_ptr_add(plt, 20);
        write32le(p,    0xe52de004); /* push {lr}         */
        write32le(p+4,  0xe59fe004); /* ldr lr, [pc, #4] */
        write32le(p+8,  0xe08fe00e); /* add lr, pc, lr    */
        write32le(p+12, 0xe5bef008); /* ldr pc, [lr, #8]! */
        /* p+16 is set in relocate_plt */
    }
    plt_offset = plt->data_offset;

    if (attr->plt_thumb_stub) {
        p = section_ptr_add(plt, 4);
        write32le(p,   0x4778); /* bx pc */
        write32le(p+2, 0x46c0); /* nop   */
    }
    p = section_ptr_add(plt, 16);
    /* Jump to GOT entry where ld.so initially put address of PLT0 */
    write32le(p,   0xe59fc004); /* ldr ip, [pc, #4] */
    write32le(p+4, 0xe08fc00c); /* add ip, pc, ip */
    write32le(p+8, 0xe59cf000); /* ldr pc, [ip] */
    /* p + 12 contains offset to GOT entry once patched by relocate_plt */
    write32le(p+12, got_offset);
    return plt_offset;
}

/* relocate the PLT: compute addresses and offsets in the PLT now that final
   address for PLT and GOT are known (see fill_program_header) */
ST_FUNC void relocate_plt(TCCState *s1)
{
    uint8_t *p, *p_end;

    if (!s1->plt)
      return;

    p = s1->plt->data;
    p_end = p + s1->plt->data_offset;

    if (p < p_end) {
        int x = s1->got->sh_addr - s1->plt->sh_addr - 12;
        write32le(s1->plt->data + 16, x - 16);
        p += 20;
        while (p < p_end) {
            if (read32le(p) == 0x46c04778) /* PLT Thumb stub present */
                p += 4;
            add32le(p + 12, x + s1->plt->data - p);
            p += 16;
        }
    }
}

void relocate_init(Section *sr) {}

void relocate(TCCState *s1, ElfW_Rel *rel, int type, unsigned char *ptr, addr_t addr, addr_t val)
{
    ElfW(Sym) *sym;
    int sym_index;

    sym_index = ELFW(R_SYM)(rel->r_info);
    sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];

    switch(type) {
        case R_ARM_PC24:
        case R_ARM_CALL:
        case R_ARM_JUMP24:
        case R_ARM_PLT32:
            {
                int x, is_thumb, is_call, h, blx_avail, is_bl, th_ko;
                x = (*(int *) ptr) & 0xffffff;
#ifdef DEBUG_RELOC
		printf ("reloc %d: x=0x%x val=0x%x ", type, x, val);
#endif
                (*(int *)ptr) &= 0xff000000;
                if (x & 0x800000)
                    x -= 0x1000000;
                x <<= 2;
                blx_avail = (TCC_CPU_VERSION >= 5);
                is_thumb = val & 1;
                is_bl = (*(unsigned *) ptr) >> 24 == 0xeb;
                is_call = (type == R_ARM_CALL || (type == R_ARM_PC24 && is_bl));
                x += val - addr;
#ifdef DEBUG_RELOC
		printf (" newx=0x%x name=%s\n", x,
			(char *) symtab_section->link->data + sym->st_name);
#endif
                h = x & 2;
                th_ko = (x & 3) && (!blx_avail || !is_call);
                if (th_ko || x >= 0x2000000 || x < -0x2000000)
                    tcc_error("can't relocate value at %x,%d",addr, type);
                x >>= 2;
                x &= 0xffffff;
                /* Only reached if blx is avail and it is a call */
                if (is_thumb) {
                    x |= h << 24;
                    (*(int *)ptr) = 0xfa << 24; /* bl -> blx */
                }
                (*(int *) ptr) |= x;
            }
            return;
        /* Since these relocations only concern Thumb-2 and blx instruction was
           introduced before Thumb-2, we can assume blx is available and not
           guard its use */
        case R_ARM_THM_PC22:
        case R_ARM_THM_JUMP24:
            {
                int x, hi, lo, s, j1, j2, i1, i2, imm10, imm11;
                int to_thumb, is_call, to_plt, blx_bit = 1 << 12;
                Section *plt;

                /* weak reference */
                if (sym->st_shndx == SHN_UNDEF &&
                    ELFW(ST_BIND)(sym->st_info) == STB_WEAK)
                    return;

                /* Get initial offset */
                hi = (*(uint16_t *)ptr);
                lo = (*(uint16_t *)(ptr+2));
                s = (hi >> 10) & 1;
                j1 = (lo >> 13) & 1;
                j2 = (lo >> 11) & 1;
                i1 = (j1 ^ s) ^ 1;
                i2 = (j2 ^ s) ^ 1;
                imm10 = hi & 0x3ff;
                imm11 = lo & 0x7ff;
                x = (s << 24) | (i1 << 23) | (i2 << 22) |
                    (imm10 << 12) | (imm11 << 1);
                if (x & 0x01000000)
                    x -= 0x02000000;

                /* Relocation infos */
                to_thumb = val & 1;
                plt = s1->plt;
                to_plt = (val >= plt->sh_addr) &&
                         (val < plt->sh_addr + plt->data_offset);
                is_call = (type == R_ARM_THM_PC22);

                if (!to_thumb && !to_plt && !is_call) {
                    int index;
                    uint8_t *p;
                    char *name, buf[1024];
                    Section *text_section;

                    name = (char *) symtab_section->link->data + sym->st_name;
                    text_section = s1->sections[sym->st_shndx];
                    /* Modify reloc to target a thumb stub to switch to ARM */
                    snprintf(buf, sizeof(buf), "%s_from_thumb", name);
                    index = put_elf_sym(symtab_section,
                                        text_section->data_offset + 1,
                                        sym->st_size, sym->st_info, 0,
                                        sym->st_shndx, buf);
                    to_thumb = 1;
                    val = text_section->data_offset + 1;
                    rel->r_info = ELFW(R_INFO)(index, type);
                    /* Create a thumb stub function to switch to ARM mode */
                    put_elf_reloc(symtab_section, text_section,
                                  text_section->data_offset + 4, R_ARM_JUMP24,
                                  sym_index);
                    p = section_ptr_add(text_section, 8);
                    write32le(p,   0x4778); /* bx pc */
                    write32le(p+2, 0x46c0); /* nop   */
                    write32le(p+4, 0xeafffffe); /* b $sym */
                }

                /* Compute final offset */
                x += val - addr;
                if (!to_thumb && is_call) {
                    blx_bit = 0; /* bl -> blx */
                    x = (x + 3) & -4; /* Compute offset from aligned PC */
                }

                /* Check that relocation is possible
                   * offset must not be out of range
                   * if target is to be entered in arm mode:
                     - bit 1 must not set
                     - instruction must be a call (bl) or a jump to PLT */
                if (!to_thumb || x >= 0x1000000 || x < -0x1000000)
                    if (to_thumb || (val & 2) || (!is_call && !to_plt))
                        tcc_error("can't relocate value at %x,%d",addr, type);

                /* Compute and store final offset */
                s = (x >> 24) & 1;
                i1 = (x >> 23) & 1;
                i2 = (x >> 22) & 1;
                j1 = s ^ (i1 ^ 1);
                j2 = s ^ (i2 ^ 1);
                imm10 = (x >> 12) & 0x3ff;
                imm11 = (x >> 1) & 0x7ff;
                (*(uint16_t *)ptr) = (uint16_t) ((hi & 0xf800) |
                                     (s << 10) | imm10);
                (*(uint16_t *)(ptr+2)) = (uint16_t) ((lo & 0xc000) |
                                (j1 << 13) | blx_bit | (j2 << 11) |
                                imm11);
            }
            return;
        case R_ARM_MOVT_ABS:
        case R_ARM_MOVW_ABS_NC:
            {
                int x, imm4, imm12;
                if (type == R_ARM_MOVT_ABS)
                    val >>= 16;
                imm12 = val & 0xfff;
                imm4 = (val >> 12) & 0xf;
                x = (imm4 << 16) | imm12;
                if (type == R_ARM_THM_MOVT_ABS)
                    *(int *)ptr |= x;
                else
                    *(int *)ptr += x;
            }
            return;
        case R_ARM_THM_MOVT_ABS:
        case R_ARM_THM_MOVW_ABS_NC:
            {
                int x, i, imm4, imm3, imm8;
                if (type == R_ARM_THM_MOVT_ABS)
                    val >>= 16;
                imm8 = val & 0xff;
                imm3 = (val >> 8) & 0x7;
                i = (val >> 11) & 1;
                imm4 = (val >> 12) & 0xf;
                x = (imm3 << 28) | (imm8 << 16) | (i << 10) | imm4;
                if (type == R_ARM_THM_MOVT_ABS)
                    *(int *)ptr |= x;
                else
                    *(int *)ptr += x;
            }
            return;
        case R_ARM_PREL31:
            {
                int x;
                x = (*(int *)ptr) & 0x7fffffff;
                (*(int *)ptr) &= 0x80000000;
                x = (x * 2) / 2;
                x += val - addr;
                if((x^(x>>1))&0x40000000)
                    tcc_error("can't relocate value at %x,%d",addr, type);
                (*(int *)ptr) |= x & 0x7fffffff;
            }
        case R_ARM_ABS32:
            *(int *)ptr += val;
            return;
        case R_ARM_REL32:
            *(int *)ptr += val - addr;
            return;
        case R_ARM_GOTPC:
            *(int *)ptr += s1->got->sh_addr - addr;
            return;
        case R_ARM_GOTOFF:
            *(int *)ptr += val - s1->got->sh_addr;
            return;
        case R_ARM_GOT32:
            /* we load the got offset */
            *(int *)ptr += s1->sym_attrs[sym_index].got_offset;
            return;
        case R_ARM_COPY:
            return;
        case R_ARM_V4BX:
            /* trade Thumb support for ARMv4 support */
            if ((0x0ffffff0 & *(int*)ptr) == 0x012FFF10)
                *(int*)ptr ^= 0xE12FFF10 ^ 0xE1A0F000; /* BX Rm -> MOV PC, Rm */
            return;
        case R_ARM_GLOB_DAT:
        case R_ARM_JUMP_SLOT:
            *(addr_t *)ptr = val;
            return;
        case R_ARM_NONE:
            /* Nothing to do.  Normally used to indicate a dependency
               on a certain symbol (like for exception handling under EABI).  */
            return;
        default:
            fprintf(stderr,"FIXME: handle reloc type %x at %x [%p] to %x\n",
                type, (unsigned)addr, ptr, (unsigned)val);
            return;
    }
}

#endif /* !TARGET_DEFS_ONLY */