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/*
* Copyright (C) 2017 ARM Ltd.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <xen/lib.h>
#include <xen/bitops.h>
#include <xen/sizes.h>
#include <asm/insn.h>
/* Mask of branch instructions' immediate. */
#define BRANCH_INSN_IMM_MASK GENMASK(23, 0)
/* Shift of branch instructions' immediate. */
#define BRANCH_INSN_IMM_SHIFT 0
static uint32_t branch_insn_encode_immediate(uint32_t insn, int32_t offset)
{
uint32_t imm;
/*
* Encode the offset to imm. All ARM32 instructions must be word aligned.
* Therefore the offset value's bits [1:0] equal to zero.
* (see ARM DDI 0406C.c A8.8.18/A8.8.25 for more encode/decode details
* about ARM32 branch instructions)
*/
imm = ((offset >> 2) & BRANCH_INSN_IMM_MASK) << BRANCH_INSN_IMM_SHIFT;
/* Update the immediate field. */
insn &= ~(BRANCH_INSN_IMM_MASK << BRANCH_INSN_IMM_SHIFT);
insn |= imm;
return insn;
}
/*
* Decode the branch offset from a branch instruction's imm field.
* The branch offset is a signed value, so it can be used to compute
* a new branch target.
*/
int32_t aarch32_get_branch_offset(uint32_t insn)
{
uint32_t imm;
/* Retrieve imm from branch instruction. */
imm = ( insn >> BRANCH_INSN_IMM_SHIFT ) & BRANCH_INSN_IMM_MASK;
/*
* Check the imm signed bit. If the imm is a negative value, we
* have to extend the imm to a full 32 bit negative value.
*/
if ( imm & BIT(23, UL) )
imm |= GENMASK(31, 24);
return (int32_t)(imm << 2);
}
/*
* Encode the displacement of a branch in the imm field and return the
* updated instruction.
*/
uint32_t aarch32_set_branch_offset(uint32_t insn, int32_t offset)
{
/* B/BL support [-32M, 32M) offset (see ARM DDI 0406C.c A4.3). */
if ( offset < -SZ_32M || offset >= SZ_32M )
{
printk(XENLOG_ERR
"%s: new branch offset out of range.\n", __func__);
return BUG_OPCODE;
}
return branch_insn_encode_immediate(insn, offset);
}
/*
* Local variables:
* mode: C
* c-file-style: "BSD"
* c-basic-offset: 4
* indent-tabs-mode: nil
* End:
*/
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