xref: /aosp_15_r20/bionic/libc/private/bionic_asm_dwarf_exprs.h (revision 8d67ca893c1523eb926b9080dbe4e2ffd2a27ba1)

/*
 * Copyright (C) 2020 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

// Define assembler macros for generating DWARF CFI instructions that use DWARF expressions.
// Assemblers don't natively support DWARF expressions, so use the C preprocessor and assembler
// macros to lower them to .cfi_escape directives.
//
// Signal trampolines need to use DWARF expressions to record the locations of saved registers,
// because the offsets from the restored SP to the saved registers is variable. e.g. A signal frame
// can have optional FP/SIMD extensions, and there may be extra padding if the interrupted SP wasn't
// aligned.

// DWARF constants.
#define DW_CFA_def_cfa_expression 0x0f
#define DW_CFA_expression 0x10
#define DW_OP_breg0 0x70
#define DW_OP_deref 0x06

// Return the size of a small uleb128 value: either 1 or 2 bytes
#define ULEB128_14BIT_SIZE(val) \
  (1 + (((val) > 0x7f) & 1))

// Return the size of a small sleb128 value: either 1 or 2 bytes
#define SLEB128_14BIT_SIZE(val)       \
  (1 + (((val) < -0x40) & 1) +        \
       (((val) > 0x3f) & 1)     )

// Output a 1 or 2-byte CFI uleb128 absolute value.
.macro m_cfi_uleb128 val
  .if (\val) < 0 || (\val) > 0x3fff
    .error "m_cfi_uleb128 value is out of range (\val)"
  .elseif (\val) > 0x7f
    .cfi_escape ((\val) & 0x7f) | 0x80
    .cfi_escape (\val) >> 7
  .else
    .cfi_escape (\val)
  .endif
.endm

// Output a 1 or 2-byte CFI sleb128 absolute value.
.macro m_cfi_sleb128 val
  .if (\val) < -0x2000 || (\val) > 0x1fff
    .error "m_cfi_sleb128 value is out of range (\val)"
  .elseif (\val) < -0x40 || (\val) > 0x3f
    .cfi_escape ((\val) & 0x7f) | 0x80
    .cfi_escape ((\val) >> 7) & 0x7f
  .else
    .cfi_escape (\val) & 0x7f
  .endif
.endm

.macro check_base_reg reg_no
  .if (\reg_no) < 0 || (\reg_no) > 31
    .error "base register is out of range for DW_OP_breg0..DW_OP_breg31 (\reg_no)"
  .endif
.endm

// Set CFA to the expression, *(base_reg + offset)
.macro m_cfi_def_cfa_deref base_reg, offset
  check_base_reg (\base_reg)
  .cfi_escape DW_CFA_def_cfa_expression
  m_cfi_uleb128 (1 + SLEB128_14BIT_SIZE(\offset) + 1)   // size of DWARF expression in bytes
  .cfi_escape DW_OP_breg0 + (\base_reg)                 // expr: 1 byte
  m_cfi_sleb128 (\offset)                               // expr: 1 or 2 bytes
  .cfi_escape DW_OP_deref                               // expr: 1 byte
.endm

// Set the address of the register's previous value to the expression, (base_reg + offset)
.macro m_cfi_breg_offset dest_reg, base_reg, offset
  check_base_reg (\base_reg)
  .cfi_escape DW_CFA_expression
  m_cfi_uleb128 (\dest_reg)
  m_cfi_uleb128 (1 + SLEB128_14BIT_SIZE(\offset)) // size of DWARF expression in bytes
  .cfi_escape DW_OP_breg0 + (\base_reg)           // expr: 1 byte
  m_cfi_sleb128 (\offset)                         // expr: 1 or 2 bytes
.endm