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1 /*
2  * Copyright (C) 2020 The Android Open Source Project
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  *  * Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  *  * Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in
12  *    the documentation and/or other materials provided with the
13  *    distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26  * SUCH DAMAGE.
27  */
28 
29 // Define assembler macros for generating DWARF CFI instructions that use DWARF expressions.
30 // Assemblers don't natively support DWARF expressions, so use the C preprocessor and assembler
31 // macros to lower them to .cfi_escape directives.
32 //
33 // Signal trampolines need to use DWARF expressions to record the locations of saved registers,
34 // because the offsets from the restored SP to the saved registers is variable. e.g. A signal frame
35 // can have optional FP/SIMD extensions, and there may be extra padding if the interrupted SP wasn't
36 // aligned.
37 
38 // DWARF constants.
39 #define DW_CFA_def_cfa_expression 0x0f
40 #define DW_CFA_expression 0x10
41 #define DW_OP_breg0 0x70
42 #define DW_OP_deref 0x06
43 
44 // Return the size of a small uleb128 value: either 1 or 2 bytes
45 #define ULEB128_14BIT_SIZE(val) \
46   (1 + (((val) > 0x7f) & 1))
47 
48 // Return the size of a small sleb128 value: either 1 or 2 bytes
49 #define SLEB128_14BIT_SIZE(val)       \
50   (1 + (((val) < -0x40) & 1) +        \
51        (((val) > 0x3f) & 1)     )
52 
53 // Output a 1 or 2-byte CFI uleb128 absolute value.
54 .macro m_cfi_uleb128 val
55   .if (\val) < 0 || (\val) > 0x3fff
56     .error "m_cfi_uleb128 value is out of range (\val)"
57   .elseif (\val) > 0x7f
58     .cfi_escape ((\val) & 0x7f) | 0x80
59     .cfi_escape (\val) >> 7
60   .else
61     .cfi_escape (\val)
62   .endif
63 .endm
64 
65 // Output a 1 or 2-byte CFI sleb128 absolute value.
66 .macro m_cfi_sleb128 val
67   .if (\val) < -0x2000 || (\val) > 0x1fff
68     .error "m_cfi_sleb128 value is out of range (\val)"
69   .elseif (\val) < -0x40 || (\val) > 0x3f
70     .cfi_escape ((\val) & 0x7f) | 0x80
71     .cfi_escape ((\val) >> 7) & 0x7f
72   .else
73     .cfi_escape (\val) & 0x7f
74   .endif
75 .endm
76 
77 .macro check_base_reg reg_no
78   .if (\reg_no) < 0 || (\reg_no) > 31
79     .error "base register is out of range for DW_OP_breg0..DW_OP_breg31 (\reg_no)"
80   .endif
81 .endm
82 
83 // Set CFA to the expression, *(base_reg + offset)
84 .macro m_cfi_def_cfa_deref base_reg, offset
85   check_base_reg (\base_reg)
86   .cfi_escape DW_CFA_def_cfa_expression
87   m_cfi_uleb128 (1 + SLEB128_14BIT_SIZE(\offset) + 1)   // size of DWARF expression in bytes
88   .cfi_escape DW_OP_breg0 + (\base_reg)                 // expr: 1 byte
89   m_cfi_sleb128 (\offset)                               // expr: 1 or 2 bytes
90   .cfi_escape DW_OP_deref                               // expr: 1 byte
91 .endm
92 
93 // Set the address of the register's previous value to the expression, (base_reg + offset)
94 .macro m_cfi_breg_offset dest_reg, base_reg, offset
95   check_base_reg (\base_reg)
96   .cfi_escape DW_CFA_expression
97   m_cfi_uleb128 (\dest_reg)
98   m_cfi_uleb128 (1 + SLEB128_14BIT_SIZE(\offset)) // size of DWARF expression in bytes
99   .cfi_escape DW_OP_breg0 + (\base_reg)           // expr: 1 byte
100   m_cfi_sleb128 (\offset)                         // expr: 1 or 2 bytes
101 .endm
102