insn.c

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#include <linux/bug.h>
#include <linux/kernel.h>
#include <asm/opcodes.h>

static unsigned long
__arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
{
    unsigned long s, j1, j2, i1, i2, imm10, imm11;
    unsigned long first, second;
    long offset;

    offset = (long)addr - (long)(pc + 4);
    if (offset < -16777216 || offset > 16777214) {
        WARN_ON_ONCE(1);
        return 0;
    }

    s   = (offset >> 24) & 0x1;
    i1  = (offset >> 23) & 0x1;
    i2  = (offset >> 22) & 0x1;
    imm10   = (offset >> 12) & 0x3ff;
    imm11   = (offset >>  1) & 0x7ff;

    j1 = (!i1) ^ s;
    j2 = (!i2) ^ s;

    first = 0xf000 | (s << 10) | imm10;
    second = 0x9000 | (j1 << 13) | (j2 << 11) | imm11;
    if (link)
        second |= 1 << 14;

    return __opcode_thumb32_compose(first, second);
}

static unsigned long
__arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
{
    unsigned long opcode = 0xea000000;
    long offset;

    if (link)
        opcode |= 1 << 24;

    offset = (long)addr - (long)(pc + 8);
    if (unlikely(offset < -33554432 || offset > 33554428)) {
        WARN_ON_ONCE(1);
        return 0;
    }

    offset = (offset >> 2) & 0x00ffffff;

    return opcode | offset;
}

unsigned long
__arm_gen_branch(unsigned long pc, unsigned long addr, bool link)
{
    if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
        return __arm_gen_branch_thumb2(pc, addr, link);
    else
        return __arm_gen_branch_arm(pc, addr, link);
}