// SPDX-License-Identifier: GPL-2.0-or-later
/*  Kernel module help for PPC64.
    Copyright (C) 2001, 2003 Rusty Russell IBM Corporation.

*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/elf.h>
#include <linux/moduleloader.h>
#include <linux/err.h>
#include <linux/vmalloc.h>
#include <linux/ftrace.h>
#include <linux/bug.h>
#include <linux/uaccess.h>
#include <asm/module.h>
#include <asm/firmware.h>
#include <asm/code-patching.h>
#include <linux/sort.h>
#include <asm/setup.h>
#include <asm/sections.h>

/* FIXME: We don't do .init separately.  To do this, we'd need to have
   a separate r2 value in the init and core section, and stub between
   them, too.

   Using a magic allocator which places modules within 32MB solves
   this, and makes other things simpler.  Anton?
   --RR.  */

#ifdef PPC64_ELF_ABI_v2

/* An address is simply the address of the function. */
typedef unsigned long func_desc_t;

static func_desc_t func_desc(unsigned long addr)
{
        return addr;
}
static unsigned long func_addr(unsigned long addr)
{
        return addr;
}
static unsigned long stub_func_addr(func_desc_t func)
{
        return func;
}

/* PowerPC64 specific values for the Elf64_Sym st_other field.  */
#define STO_PPC64_LOCAL_BIT     5
#define STO_PPC64_LOCAL_MASK    (7 << STO_PPC64_LOCAL_BIT)
#define PPC64_LOCAL_ENTRY_OFFSET(other)                                 \
 (((1 << (((other) & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT)) >> 2) << 2)

static unsigned int local_entry_offset(const Elf64_Sym *sym)
{
        /* sym->st_other indicates offset to local entry point
         * (otherwise it will assume r12 is the address of the start
         * of function and try to derive r2 from it). */
        return PPC64_LOCAL_ENTRY_OFFSET(sym->st_other);
}
#else

/* An address is address of the OPD entry, which contains address of fn. */
typedef struct ppc64_opd_entry func_desc_t;

static func_desc_t func_desc(unsigned long addr)
{
        return *(struct ppc64_opd_entry *)addr;
}
static unsigned long func_addr(unsigned long addr)
{
        return func_desc(addr).funcaddr;
}
static unsigned long stub_func_addr(func_desc_t func)
{
        return func.funcaddr;
}
static unsigned int local_entry_offset(const Elf64_Sym *sym)
{
        return 0;
}

void *dereference_module_function_descriptor(struct module *mod, void *ptr)
{
        if (ptr < (void *)mod->arch.start_opd ||
                        ptr >= (void *)mod->arch.end_opd)
                return ptr;

        return dereference_function_descriptor(ptr);
}
#endif

#define STUB_MAGIC 0x73747562 /* stub */

/* Like PPC32, we need little trampolines to do > 24-bit jumps (into
   the kernel itself).  But on PPC64, these need to be used for every
   jump, actually, to reset r2 (TOC+0x8000). */
struct ppc64_stub_entry
{
        /* 28 byte jump instruction sequence (7 instructions). We only
         * need 6 instructions on ABIv2 but we always allocate 7 so
         * so we don't have to modify the trampoline load instruction. */
        u32 jump[7];
        /* Used by ftrace to identify stubs */
        u32 magic;
        /* Data for the above code */
        func_desc_t funcdata;
};

/*
 * PPC64 uses 24 bit jumps, but we need to jump into other modules or
 * the kernel which may be further.  So we jump to a stub.
 *
 * For ELFv1 we need to use this to set up the new r2 value (aka TOC
 * pointer).  For ELFv2 it's the callee's responsibility to set up the
 * new r2, but for both we need to save the old r2.
 *
 * We could simply patch the new r2 value and function pointer into
 * the stub, but it's significantly shorter to put these values at the
 * end of the stub code, and patch the stub address (32-bits relative
 * to the TOC ptr, r2) into the stub.
 *
 * addis   r11,r2, <high>
 * addi    r11,r11, <low>
 * std     r2,R2_STACK_OFFSET(r1)
 * ld      r12,32(r11)
 * ld      r2,40(r11)
 * mtctr   r12
 * bctr
 */
static u32 ppc64_stub_insns[] = {
        PPC_INST_ADDIS | __PPC_RT(R11) | __PPC_RA(R2),
        PPC_INST_ADDI | __PPC_RT(R11) | __PPC_RA(R11),
        /* Save current r2 value in magic place on the stack. */
        PPC_INST_STD | __PPC_RS(R2) | __PPC_RA(R1) | R2_STACK_OFFSET,
        PPC_INST_LD | __PPC_RT(R12) | __PPC_RA(R11) | 32,
#ifdef PPC64_ELF_ABI_v1
        /* Set up new r2 from function descriptor */
        PPC_INST_LD | __PPC_RT(R2) | __PPC_RA(R11) | 40,
#endif
        PPC_INST_MTCTR | __PPC_RS(R12),
        PPC_INST_BCTR,
};

#ifdef CONFIG_DYNAMIC_FTRACE
int module_trampoline_target(struct module *mod, unsigned long addr,
                             unsigned long *target)
{
        struct ppc64_stub_entry *stub;
        func_desc_t funcdata;
        u32 magic;

        if (!within_module_core(addr, mod)) {
                pr_err("%s: stub %lx not in module %s\n", __func__, addr, mod->name);
                return -EFAULT;
        }

        stub = (struct ppc64_stub_entry *)addr;

        if (probe_kernel_read(&magic, &stub->magic, sizeof(magic))) {
                pr_err("%s: fault reading magic for stub %lx for %s\n", __func__, addr, mod->name);
                return -EFAULT;
        }

        if (magic != STUB_MAGIC) {
                pr_err("%s: bad magic for stub %lx for %s\n", __func__, addr, mod->name);
                return -EFAULT;
        }

        if (probe_kernel_read(&funcdata, &stub->funcdata, sizeof(funcdata))) {
                pr_err("%s: fault reading funcdata for stub %lx for %s\n", __func__, addr, mod->name);
                return -EFAULT;
        }

        *target = stub_func_addr(funcdata);

        return 0;
}
#endif

/* Count how many different 24-bit relocations (different symbol,
   different addend) */
static unsigned int count_relocs(const Elf64_Rela *rela, unsigned int num)
{
        unsigned int i, r_info, r_addend, _count_relocs;

        /* FIXME: Only count external ones --RR */
        _count_relocs = 0;
        r_info = 0;
        r_addend = 0;
        for (i = 0; i < num; i++)
                /* Only count 24-bit relocs, others don't need stubs */
                if (ELF64_R_TYPE(rela[i].r_info) == R_PPC_REL24 &&
                    (r_info != ELF64_R_SYM(rela[i].r_info) ||
                     r_addend != rela[i].r_addend)) {
                        _count_relocs++;
                        r_info = ELF64_R_SYM(rela[i].r_info);
                        r_addend = rela[i].r_addend;
                }

        return _count_relocs;
}

static int relacmp(const void *_x, const void *_y)
{
        const Elf64_Rela *x, *y;

        y = (Elf64_Rela *)_x;
        x = (Elf64_Rela *)_y;

        /* Compare the entire r_info (as opposed to ELF64_R_SYM(r_info) only) to
         * make the comparison cheaper/faster. It won't affect the sorting or
         * the counting algorithms' performance
         */
        if (x->r_info < y->r_info)
                return -1;
        else if (x->r_info > y->r_info)
                return 1;
        else if (x->r_addend < y->r_addend)
                return -1;
        else if (x->r_addend > y->r_addend)
                return 1;
        else
                return 0;
}

static void relaswap(void *_x, void *_y, int size)
{
        uint64_t *x, *y, tmp;
        int i;

        y = (uint64_t *)_x;
        x = (uint64_t *)_y;

        for (i = 0; i < sizeof(Elf64_Rela) / sizeof(uint64_t); i++) {
                tmp = x[i];
                x[i] = y[i];
                y[i] = tmp;
        }
}

/* Get size of potential trampolines required. */
static unsigned long get_stubs_size(const Elf64_Ehdr *hdr,
                                    const Elf64_Shdr *sechdrs)
{
        /* One extra reloc so it's always 0-funcaddr terminated */
        unsigned long relocs = 1;
        unsigned i;

        /* Every relocated section... */
        for (i = 1; i < hdr->e_shnum; i++) {
                if (sechdrs[i].sh_type == SHT_RELA) {
                        pr_debug("Found relocations in section %u\n", i);
                        pr_debug("Ptr: %p.  Number: %Lu\n",
                               (void *)sechdrs[i].sh_addr,
                               sechdrs[i].sh_size / sizeof(Elf64_Rela));

                        /* Sort the relocation information based on a symbol and
                         * addend key. This is a stable O(n*log n) complexity
                         * alogrithm but it will reduce the complexity of
                         * count_relocs() to linear complexity O(n)
                         */
                        sort((void *)sechdrs[i].sh_addr,
                             sechdrs[i].sh_size / sizeof(Elf64_Rela),
                             sizeof(Elf64_Rela), relacmp, relaswap);

                        relocs += count_relocs((void *)sechdrs[i].sh_addr,
                                               sechdrs[i].sh_size
                                               / sizeof(Elf64_Rela));
                }
        }

#ifdef CONFIG_DYNAMIC_FTRACE
        /* make the trampoline to the ftrace_caller */
        relocs++;
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
        /* an additional one for ftrace_regs_caller */
        relocs++;
#endif
#endif

        pr_debug("Looks like a total of %lu stubs, max\n", relocs);
        return relocs * sizeof(struct ppc64_stub_entry);
}

/* Still needed for ELFv2, for .TOC. */
static void dedotify_versions(struct modversion_info *vers,
                              unsigned long size)
{
        struct modversion_info *end;

        for (end = (void *)vers + size; vers < end; vers++)
                if (vers->name[0] == '.') {
                        memmove(vers->name, vers->name+1, strlen(vers->name));
                }
}

/*
 * Undefined symbols which refer to .funcname, hack to funcname. Make .TOC.
 * seem to be defined (value set later).
 */
static void dedotify(Elf64_Sym *syms, unsigned int numsyms, char *strtab)
{
        unsigned int i;

        for (i = 1; i < numsyms; i++) {
                if (syms[i].st_shndx == SHN_UNDEF) {
                        char *name = strtab + syms[i].st_name;
                        if (name[0] == '.') {
                                if (strcmp(name+1, "TOC.") == 0)
                                        syms[i].st_shndx = SHN_ABS;
                                syms[i].st_name++;
                        }
                }
        }
}

static Elf64_Sym *find_dot_toc(Elf64_Shdr *sechdrs,
                               const char *strtab,
                               unsigned int symindex)
{
        unsigned int i, numsyms;
        Elf64_Sym *syms;

        syms = (Elf64_Sym *)sechdrs[symindex].sh_addr;
        numsyms = sechdrs[symindex].sh_size / sizeof(Elf64_Sym);

        for (i = 1; i < numsyms; i++) {
                if (syms[i].st_shndx == SHN_ABS
                    && strcmp(strtab + syms[i].st_name, "TOC.") == 0)
                        return &syms[i];
        }
        return NULL;
}

int module_frob_arch_sections(Elf64_Ehdr *hdr,
                              Elf64_Shdr *sechdrs,
                              char *secstrings,
                              struct module *me)
{
        unsigned int i;

        /* Find .toc and .stubs sections, symtab and strtab */
        for (i = 1; i < hdr->e_shnum; i++) {
                char *p;
                if (strcmp(secstrings + sechdrs[i].sh_name, ".stubs") == 0)
                        me->arch.stubs_section = i;
                else if (strcmp(secstrings + sechdrs[i].sh_name, ".toc") == 0) {
                        me->arch.toc_section = i;
                        if (sechdrs[i].sh_addralign < 8)
                                sechdrs[i].sh_addralign = 8;
                }
                else if (strcmp(secstrings+sechdrs[i].sh_name,"__versions")==0)
                        dedotify_versions((void *)hdr + sechdrs[i].sh_offset,
                                          sechdrs[i].sh_size);

                /* We don't handle .init for the moment: rename to _init */
                while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
                        p[0] = '_';

                if (sechdrs[i].sh_type == SHT_SYMTAB)
                        dedotify((void *)hdr + sechdrs[i].sh_offset,
                                 sechdrs[i].sh_size / sizeof(Elf64_Sym),
                                 (void *)hdr
                                 + sechdrs[sechdrs[i].sh_link].sh_offset);
        }

        if (!me->arch.stubs_section) {
                pr_err("%s: doesn't contain .stubs.\n", me->name);
                return -ENOEXEC;
        }

        /* If we don't have a .toc, just use .stubs.  We need to set r2
           to some reasonable value in case the module calls out to
           other functions via a stub, or if a function pointer escapes
           the module by some means.  */
        if (!me->arch.toc_section)
                me->arch.toc_section = me->arch.stubs_section;

        /* Override the stubs size */
        sechdrs[me->arch.stubs_section].sh_size = get_stubs_size(hdr, sechdrs);
        return 0;
}

/*
 * r2 is the TOC pointer: it actually points 0x8000 into the TOC (this gives the
 * value maximum span in an instruction which uses a signed offset). Round down
 * to a 256 byte boundary for the odd case where we are setting up r2 without a
 * .toc section.
 */
static inline unsigned long my_r2(const Elf64_Shdr *sechdrs, struct module *me)
{
        return (sechdrs[me->arch.toc_section].sh_addr & ~0xfful) + 0x8000;
}

/* Patch stub to reference function and correct r2 value. */
static inline int create_stub(const Elf64_Shdr *sechdrs,
                              struct ppc64_stub_entry *entry,
                              unsigned long addr,
                              struct module *me)
{
        long reladdr;

        memcpy(entry->jump, ppc64_stub_insns, sizeof(ppc64_stub_insns));

        /* Stub uses address relative to r2. */
        reladdr = (unsigned long)entry - my_r2(sechdrs, me);
        if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
                pr_err("%s: Address %p of stub out of range of %p.\n",
                       me->name, (void *)reladdr, (void *)my_r2);
                return 0;
        }
        pr_debug("Stub %p get data from reladdr %li\n", entry, reladdr);

        entry->jump[0] |= PPC_HA(reladdr);
        entry->jump[1] |= PPC_LO(reladdr);
        entry->funcdata = func_desc(addr);
        entry->magic = STUB_MAGIC;

        return 1;
}

/* Create stub to jump to function described in this OPD/ptr: we need the
   stub to set up the TOC ptr (r2) for the function. */
static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
                                   unsigned long addr,
                                   struct module *me)
{
        struct ppc64_stub_entry *stubs;
        unsigned int i, num_stubs;

        num_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*stubs);

        /* Find this stub, or if that fails, the next avail. entry */
        stubs = (void *)sechdrs[me->arch.stubs_section].sh_addr;
        for (i = 0; stub_func_addr(stubs[i].funcdata); i++) {
                if (WARN_ON(i >= num_stubs))
                        return 0;

                if (stub_func_addr(stubs[i].funcdata) == func_addr(addr))
                        return (unsigned long)&stubs[i];
        }

        if (!create_stub(sechdrs, &stubs[i], addr, me))
                return 0;

        return (unsigned long)&stubs[i];
}

#ifdef CONFIG_MPROFILE_KERNEL
static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
{
        if (strcmp("_mcount", name))
                return false;

        /*
         * Check if this is one of the -mprofile-kernel sequences.
         */
        if (instruction[-1] == PPC_INST_STD_LR &&
            instruction[-2] == PPC_INST_MFLR)
                return true;

        if (instruction[-1] == PPC_INST_MFLR)
                return true;

        return false;
}

/*
 * In case of _mcount calls, do not save the current callee's TOC (in r2) into
 * the original caller's stack frame. If we did we would clobber the saved TOC
 * value of the original caller.
 */
static void squash_toc_save_inst(const char *name, unsigned long addr)
{
        struct ppc64_stub_entry *stub = (struct ppc64_stub_entry *)addr;

        /* Only for calls to _mcount */
        if (strcmp("_mcount", name) != 0)
                return;

        stub->jump[2] = PPC_INST_NOP;
}
#else
static void squash_toc_save_inst(const char *name, unsigned long addr) { }

static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
{
        return false;
}
#endif

/* We expect a noop next: if it is, replace it with instruction to
   restore r2. */
static int restore_r2(const char *name, u32 *instruction, struct module *me)
{
        u32 *prev_insn = instruction - 1;

        if (is_mprofile_mcount_callsite(name, prev_insn))
                return 1;

        /*
         * Make sure the branch isn't a sibling call.  Sibling calls aren't
         * "link" branches and they don't return, so they don't need the r2
         * restore afterwards.
         */
        if (!instr_is_relative_link_branch(*prev_insn))
                return 1;

        if (*instruction != PPC_INST_NOP) {
                pr_err("%s: Expected nop after call, got %08x at %pS\n",
                        me->name, *instruction, instruction);
                return 0;
        }
        /* ld r2,R2_STACK_OFFSET(r1) */
        *instruction = PPC_INST_LD_TOC;
        return 1;
}

int apply_relocate_add(Elf64_Shdr *sechdrs,
                       const char *strtab,
                       unsigned int symindex,
                       unsigned int relsec,
                       struct module *me)
{
        unsigned int i;
        Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
        Elf64_Sym *sym;
        unsigned long *location;
        unsigned long value;

        pr_debug("Applying ADD relocate section %u to %u\n", relsec,
               sechdrs[relsec].sh_info);

        /* First time we're called, we can fix up .TOC. */
        if (!me->arch.toc_fixed) {
                sym = find_dot_toc(sechdrs, strtab, symindex);
                /* It's theoretically possible that a module doesn't want a
                 * .TOC. so don't fail it just for that. */
                if (sym)
                        sym->st_value = my_r2(sechdrs, me);
                me->arch.toc_fixed = true;
        }

        for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
                /* This is where to make the change */
                location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
                        + rela[i].r_offset;
                /* This is the symbol it is referring to */
                sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
                        + ELF64_R_SYM(rela[i].r_info);

                pr_debug("RELOC at %p: %li-type as %s (0x%lx) + %li\n",
                       location, (long)ELF64_R_TYPE(rela[i].r_info),
                       strtab + sym->st_name, (unsigned long)sym->st_value,
                       (long)rela[i].r_addend);

                /* `Everything is relative'. */
                value = sym->st_value + rela[i].r_addend;

                switch (ELF64_R_TYPE(rela[i].r_info)) {
                case R_PPC64_ADDR32:
                        /* Simply set it */
                        *(u32 *)location = value;
                        break;

                case R_PPC64_ADDR64:
                        /* Simply set it */
                        *(unsigned long *)location = value;
                        break;

                case R_PPC64_TOC:
                        *(unsigned long *)location = my_r2(sechdrs, me);
                        break;

                case R_PPC64_TOC16:
                        /* Subtract TOC pointer */
                        value -= my_r2(sechdrs, me);
                        if (value + 0x8000 > 0xffff) {
                                pr_err("%s: bad TOC16 relocation (0x%lx)\n",
                                       me->name, value);
                                return -ENOEXEC;
                        }
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xffff)
                                | (value & 0xffff);
                        break;

                case R_PPC64_TOC16_LO:
                        /* Subtract TOC pointer */
                        value -= my_r2(sechdrs, me);
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xffff)
                                | (value & 0xffff);
                        break;

                case R_PPC64_TOC16_DS:
                        /* Subtract TOC pointer */
                        value -= my_r2(sechdrs, me);
                        if ((value & 3) != 0 || value + 0x8000 > 0xffff) {
                                pr_err("%s: bad TOC16_DS relocation (0x%lx)\n",
                                       me->name, value);
                                return -ENOEXEC;
                        }
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xfffc)
                                | (value & 0xfffc);
                        break;

                case R_PPC64_TOC16_LO_DS:
                        /* Subtract TOC pointer */
                        value -= my_r2(sechdrs, me);
                        if ((value & 3) != 0) {
                                pr_err("%s: bad TOC16_LO_DS relocation (0x%lx)\n",
                                       me->name, value);
                                return -ENOEXEC;
                        }
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xfffc)
                                | (value & 0xfffc);
                        break;

                case R_PPC64_TOC16_HA:
                        /* Subtract TOC pointer */
                        value -= my_r2(sechdrs, me);
                        value = ((value + 0x8000) >> 16);
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xffff)
                                | (value & 0xffff);
                        break;

                case R_PPC_REL24:
                        /* FIXME: Handle weak symbols here --RR */
                        if (sym->st_shndx == SHN_UNDEF ||
                            sym->st_shndx == SHN_LIVEPATCH) {
                                /* External: go via stub */
                                value = stub_for_addr(sechdrs, value, me);
                                if (!value)
                                        return -ENOENT;
                                if (!restore_r2(strtab + sym->st_name,
                                                        (u32 *)location + 1, me))
                                        return -ENOEXEC;

                                squash_toc_save_inst(strtab + sym->st_name, value);
                        } else
                                value += local_entry_offset(sym);

                        /* Convert value to relative */
                        value -= (unsigned long)location;
                        if (value + 0x2000000 > 0x3ffffff || (value & 3) != 0){
                                pr_err("%s: REL24 %li out of range!\n",
                                       me->name, (long int)value);
                                return -ENOEXEC;
                        }

                        /* Only replace bits 2 through 26 */
                        *(uint32_t *)location
                                = (*(uint32_t *)location & ~0x03fffffc)
                                | (value & 0x03fffffc);
                        break;

                case R_PPC64_REL64:
                        /* 64 bits relative (used by features fixups) */
                        *location = value - (unsigned long)location;
                        break;

                case R_PPC64_REL32:
                        /* 32 bits relative (used by relative exception tables) */
                        /* Convert value to relative */
                        value -= (unsigned long)location;
                        if (value + 0x80000000 > 0xffffffff) {
                                pr_err("%s: REL32 %li out of range!\n",
                                       me->name, (long int)value);
                                return -ENOEXEC;
                        }
                        *(u32 *)location = value;
                        break;

                case R_PPC64_TOCSAVE:
                        /*
                         * Marker reloc indicates we don't have to save r2.
                         * That would only save us one instruction, so ignore
                         * it.
                         */
                        break;

                case R_PPC64_ENTRY:
                        /*
                         * Optimize ELFv2 large code model entry point if
                         * the TOC is within 2GB range of current location.
                         */
                        value = my_r2(sechdrs, me) - (unsigned long)location;
                        if (value + 0x80008000 > 0xffffffff)
                                break;
                        /*
                         * Check for the large code model prolog sequence:
                         *      ld r2, ...(r12)
                         *      add r2, r2, r12
                         */
                        if ((((uint32_t *)location)[0] & ~0xfffc) !=
                            (PPC_INST_LD | __PPC_RT(R2) | __PPC_RA(R12)))
                                break;
                        if (((uint32_t *)location)[1] !=
                            (PPC_INST_ADD | __PPC_RT(R2) | __PPC_RA(R2) | __PPC_RB(R12)))
                                break;
                        /*
                         * If found, replace it with:
                         *      addis r2, r12, (.TOC.-func)@ha
                         *      addi  r2,  r2, (.TOC.-func)@l
                         */
                        ((uint32_t *)location)[0] = PPC_INST_ADDIS | __PPC_RT(R2) |
                                                    __PPC_RA(R12) | PPC_HA(value);
                        ((uint32_t *)location)[1] = PPC_INST_ADDI | __PPC_RT(R2) |
                                                    __PPC_RA(R2) | PPC_LO(value);
                        break;

                case R_PPC64_REL16_HA:
                        /* Subtract location pointer */
                        value -= (unsigned long)location;
                        value = ((value + 0x8000) >> 16);
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xffff)
                                | (value & 0xffff);
                        break;

                case R_PPC64_REL16_LO:
                        /* Subtract location pointer */
                        value -= (unsigned long)location;
                        *((uint16_t *) location)
                                = (*((uint16_t *) location) & ~0xffff)
                                | (value & 0xffff);
                        break;

                default:
                        pr_err("%s: Unknown ADD relocation: %lu\n",
                               me->name,
                               (unsigned long)ELF64_R_TYPE(rela[i].r_info));
                        return -ENOEXEC;
                }
        }

        return 0;
}

#ifdef CONFIG_DYNAMIC_FTRACE

#ifdef CONFIG_MPROFILE_KERNEL

#define PACATOC offsetof(struct paca_struct, kernel_toc)

/*
 * For mprofile-kernel we use a special stub for ftrace_caller() because we
 * can't rely on r2 containing this module's TOC when we enter the stub.
 *
 * That can happen if the function calling us didn't need to use the toc. In
 * that case it won't have setup r2, and the r2 value will be either the
 * kernel's toc, or possibly another modules toc.
 *
 * To deal with that this stub uses the kernel toc, which is always accessible
 * via the paca (in r13). The target (ftrace_caller()) is responsible for
 * saving and restoring the toc before returning.
 */
static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs,
                                struct module *me, unsigned long addr)
{
        struct ppc64_stub_entry *entry;
        unsigned int i, num_stubs;
        /*
         * ld      r12,PACATOC(r13)
         * addis   r12,r12,<high>
         * addi    r12,r12,<low>
         * mtctr   r12
         * bctr
         */
        static u32 stub_insns[] = {
                PPC_INST_LD | __PPC_RT(R12) | __PPC_RA(R13) | PACATOC,
                PPC_INST_ADDIS | __PPC_RT(R12) | __PPC_RA(R12),
                PPC_INST_ADDI | __PPC_RT(R12) | __PPC_RA(R12),
                PPC_INST_MTCTR | __PPC_RS(R12),
                PPC_INST_BCTR,
        };
        long reladdr;

        num_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*entry);

        /* Find the next available stub entry */
        entry = (void *)sechdrs[me->arch.stubs_section].sh_addr;
        for (i = 0; i < num_stubs && stub_func_addr(entry->funcdata); i++, entry++);

        if (i >= num_stubs) {
                pr_err("%s: Unable to find a free slot for ftrace stub.\n", me->name);
                return 0;
        }

        memcpy(entry->jump, stub_insns, sizeof(stub_insns));

        /* Stub uses address relative to kernel toc (from the paca) */
        reladdr = addr - kernel_toc_addr();
        if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
                pr_err("%s: Address of %ps out of range of kernel_toc.\n",
                                                        me->name, (void *)addr);
                return 0;
        }

        entry->jump[1] |= PPC_HA(reladdr);
        entry->jump[2] |= PPC_LO(reladdr);

        /* Eventhough we don't use funcdata in the stub, it's needed elsewhere. */
        entry->funcdata = func_desc(addr);
        entry->magic = STUB_MAGIC;

        return (unsigned long)entry;
}
#else
static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs,
                                struct module *me, unsigned long addr)
{
        return stub_for_addr(sechdrs, addr, me);
}
#endif

int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
{
        mod->arch.tramp = create_ftrace_stub(sechdrs, mod,
                                        (unsigned long)ftrace_caller);
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
        mod->arch.tramp_regs = create_ftrace_stub(sechdrs, mod,
                                        (unsigned long)ftrace_regs_caller);
        if (!mod->arch.tramp_regs)
                return -ENOENT;
#endif

        if (!mod->arch.tramp)
                return -ENOENT;

        return 0;
}
#endif