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 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //
 // Darwin's alternative to DWARF based unwind encodings.
 //
 //===----------------------------------------------------------------------===//
 
 
 #ifndef __COMPACT_UNWIND_ENCODING__
 #define __COMPACT_UNWIND_ENCODING__
 
 #include <stdint.h>
 
 //
 // Compilers can emit standard DWARF FDEs in the __TEXT,__eh_frame section
 // of object files. Or compilers can emit compact unwind information in
 // the __LD,__compact_unwind section.
 //
 // When the linker creates a final linked image, it will create a
 // __TEXT,__unwind_info section.  This section is a small and fast way for the
 // runtime to access unwind info for any given function.  If the compiler
 // emitted compact unwind info for the function, that compact unwind info will
 // be encoded in the __TEXT,__unwind_info section. If the compiler emitted
 // DWARF unwind info, the __TEXT,__unwind_info section will contain the offset
 // of the FDE in the __TEXT,__eh_frame section in the final linked image.
 //
 // Note: Previously, the linker would transform some DWARF unwind infos into
 //       compact unwind info.  But that is fragile and no longer done.
 
 
 //
 // The compact unwind encoding is a 32-bit value which encoded in an
 // architecture specific way, which registers to restore from where, and how
 // to unwind out of the function.
 //
 typedef uint32_t compact_unwind_encoding_t;
 
 
 // architecture independent bits
 enum {
     UNWIND_IS_NOT_FUNCTION_START           = 0x80000000,
     UNWIND_HAS_LSDA                        = 0x40000000,
     UNWIND_PERSONALITY_MASK                = 0x30000000,
 };
 
 
 
 
 //
 // x86
 //
 // 1-bit: start
 // 1-bit: has lsda
 // 2-bit: personality index
 //
 // 4-bits: 0=old, 1=ebp based, 2=stack-imm, 3=stack-ind, 4=DWARF
 //  ebp based:
 //        15-bits (5*3-bits per reg) register permutation
 //        8-bits for stack offset
 //  frameless:
 //        8-bits stack size
 //        3-bits stack adjust
 //        3-bits register count
 //        10-bits register permutation
 //
 enum {
     UNWIND_X86_MODE_MASK                         = 0x0F000000,
     UNWIND_X86_MODE_EBP_FRAME                    = 0x01000000,
     UNWIND_X86_MODE_STACK_IMMD                   = 0x02000000,
     UNWIND_X86_MODE_STACK_IND                    = 0x03000000,
     UNWIND_X86_MODE_DWARF                        = 0x04000000,
 
     UNWIND_X86_EBP_FRAME_REGISTERS               = 0x00007FFF,
     UNWIND_X86_EBP_FRAME_OFFSET                  = 0x00FF0000,
 
     UNWIND_X86_FRAMELESS_STACK_SIZE              = 0x00FF0000,
     UNWIND_X86_FRAMELESS_STACK_ADJUST            = 0x0000E000,
     UNWIND_X86_FRAMELESS_STACK_REG_COUNT         = 0x00001C00,
     UNWIND_X86_FRAMELESS_STACK_REG_PERMUTATION   = 0x000003FF,
 
     UNWIND_X86_DWARF_SECTION_OFFSET              = 0x00FFFFFF,
 };
 
 enum {
     UNWIND_X86_REG_NONE     = 0,
     UNWIND_X86_REG_EBX      = 1,
     UNWIND_X86_REG_ECX      = 2,
     UNWIND_X86_REG_EDX      = 3,
     UNWIND_X86_REG_EDI      = 4,
     UNWIND_X86_REG_ESI      = 5,
     UNWIND_X86_REG_EBP      = 6,
 };
 
 //
 // For x86 there are four modes for the compact unwind encoding:
 // UNWIND_X86_MODE_EBP_FRAME:
 //    EBP based frame where EBP is push on stack immediately after return address,
 //    then ESP is moved to EBP. Thus, to unwind ESP is restored with the current
 //    EPB value, then EBP is restored by popping off the stack, and the return
 //    is done by popping the stack once more into the pc.
 //    All non-volatile registers that need to be restored must have been saved
 //    in a small range in the stack that starts EBP-4 to EBP-1020.  The offset/4
 //    is encoded in the UNWIND_X86_EBP_FRAME_OFFSET bits.  The registers saved
 //    are encoded in the UNWIND_X86_EBP_FRAME_REGISTERS bits as five 3-bit entries.
 //    Each entry contains which register to restore.
 // UNWIND_X86_MODE_STACK_IMMD:
 //    A "frameless" (EBP not used as frame pointer) function with a small
 //    constant stack size.  To return, a constant (encoded in the compact
 //    unwind encoding) is added to the ESP. Then the return is done by
 //    popping the stack into the pc.
 //    All non-volatile registers that need to be restored must have been saved
 //    on the stack immediately after the return address.  The stack_size/4 is
 //    encoded in the UNWIND_X86_FRAMELESS_STACK_SIZE (max stack size is 1024).
 //    The number of registers saved is encoded in UNWIND_X86_FRAMELESS_STACK_REG_COUNT.
 //    UNWIND_X86_FRAMELESS_STACK_REG_PERMUTATION contains which registers were
 //    saved and their order.
 // UNWIND_X86_MODE_STACK_IND:
 //    A "frameless" (EBP not used as frame pointer) function large constant
 //    stack size.  This case is like the previous, except the stack size is too
 //    large to encode in the compact unwind encoding.  Instead it requires that
 //    the function contains "subl $nnnnnnnn,ESP" in its prolog.  The compact
 //    encoding contains the offset to the nnnnnnnn value in the function in
 //    UNWIND_X86_FRAMELESS_STACK_SIZE.
 // UNWIND_X86_MODE_DWARF:
 //    No compact unwind encoding is available.  Instead the low 24-bits of the
 //    compact encoding is the offset of the DWARF FDE in the __eh_frame section.
 //    This mode is never used in object files.  It is only generated by the
 //    linker in final linked images which have only DWARF unwind info for a
 //    function.
 //
 // The permutation encoding is a Lehmer code sequence encoded into a
 // single variable-base number so we can encode the ordering of up to
 // six registers in a 10-bit space.
 //
 // The following is the algorithm used to create the permutation encoding used
 // with frameless stacks.  It is passed the number of registers to be saved and
 // an array of the register numbers saved.
 //
 //uint32_t permute_encode(uint32_t registerCount, const uint32_t registers[6])
 //{
 //    uint32_t renumregs[6];
 //    for (int i=6-registerCount; i < 6; ++i) {
 //        int countless = 0;
 //        for (int j=6-registerCount; j < i; ++j) {
 //            if ( registers[j] < registers[i] )
 //                ++countless;
 //        }
 //        renumregs[i] = registers[i] - countless -1;
 //    }
 //    uint32_t permutationEncoding = 0;
 //    switch ( registerCount ) {
 //        case 6:
 //            permutationEncoding |= (120*renumregs[0] + 24*renumregs[1]
 //                                    + 6*renumregs[2] + 2*renumregs[3]
 //                                      + renumregs[4]);
 //            break;
 //        case 5:
 //            permutationEncoding |= (120*renumregs[1] + 24*renumregs[2]
 //                                    + 6*renumregs[3] + 2*renumregs[4]
 //                                      + renumregs[5]);
 //            break;
 //        case 4:
 //            permutationEncoding |= (60*renumregs[2] + 12*renumregs[3]
 //                                   + 3*renumregs[4] + renumregs[5]);
 //            break;
 //        case 3:
 //            permutationEncoding |= (20*renumregs[3] + 4*renumregs[4]
 //                                     + renumregs[5]);
 //            break;
 //        case 2:
 //            permutationEncoding |= (5*renumregs[4] + renumregs[5]);
 //            break;
 //        case 1:
 //            permutationEncoding |= (renumregs[5]);
 //            break;
 //    }
 //    return permutationEncoding;
 //}
 //
 
 
 
 
 //
 // x86_64
 //
 // 1-bit: start
 // 1-bit: has lsda
 // 2-bit: personality index
 //
 // 4-bits: 0=old, 1=rbp based, 2=stack-imm, 3=stack-ind, 4=DWARF
 //  rbp based:
 //        15-bits (5*3-bits per reg) register permutation
 //        8-bits for stack offset
 //  frameless:
 //        8-bits stack size
 //        3-bits stack adjust
 //        3-bits register count
 //        10-bits register permutation
 //
 enum {
     UNWIND_X86_64_MODE_MASK                         = 0x0F000000,
     UNWIND_X86_64_MODE_RBP_FRAME                    = 0x01000000,
     UNWIND_X86_64_MODE_STACK_IMMD                   = 0x02000000,
     UNWIND_X86_64_MODE_STACK_IND                    = 0x03000000,
     UNWIND_X86_64_MODE_DWARF                        = 0x04000000,
 
     UNWIND_X86_64_RBP_FRAME_REGISTERS               = 0x00007FFF,
     UNWIND_X86_64_RBP_FRAME_OFFSET                  = 0x00FF0000,
 
     UNWIND_X86_64_FRAMELESS_STACK_SIZE              = 0x00FF0000,
     UNWIND_X86_64_FRAMELESS_STACK_ADJUST            = 0x0000E000,
     UNWIND_X86_64_FRAMELESS_STACK_REG_COUNT         = 0x00001C00,
     UNWIND_X86_64_FRAMELESS_STACK_REG_PERMUTATION   = 0x000003FF,
 
     UNWIND_X86_64_DWARF_SECTION_OFFSET              = 0x00FFFFFF,
 };
 
 enum {
     UNWIND_X86_64_REG_NONE       = 0,
     UNWIND_X86_64_REG_RBX        = 1,
     UNWIND_X86_64_REG_R12        = 2,
     UNWIND_X86_64_REG_R13        = 3,
     UNWIND_X86_64_REG_R14        = 4,
     UNWIND_X86_64_REG_R15        = 5,
     UNWIND_X86_64_REG_RBP        = 6,
 };
 //
 // For x86_64 there are four modes for the compact unwind encoding:
 // UNWIND_X86_64_MODE_RBP_FRAME:
 //    RBP based frame where RBP is push on stack immediately after return address,
 //    then RSP is moved to RBP. Thus, to unwind RSP is restored with the current
 //    EPB value, then RBP is restored by popping off the stack, and the return
 //    is done by popping the stack once more into the pc.
 //    All non-volatile registers that need to be restored must have been saved
 //    in a small range in the stack that starts RBP-8 to RBP-2040.  The offset/8
 //    is encoded in the UNWIND_X86_64_RBP_FRAME_OFFSET bits.  The registers saved
 //    are encoded in the UNWIND_X86_64_RBP_FRAME_REGISTERS bits as five 3-bit entries.
 //    Each entry contains which register to restore.
 // UNWIND_X86_64_MODE_STACK_IMMD:
 //    A "frameless" (RBP not used as frame pointer) function with a small
 //    constant stack size.  To return, a constant (encoded in the compact
 //    unwind encoding) is added to the RSP. Then the return is done by
 //    popping the stack into the pc.
 //    All non-volatile registers that need to be restored must have been saved
 //    on the stack immediately after the return address.  The stack_size/8 is
 //    encoded in the UNWIND_X86_64_FRAMELESS_STACK_SIZE (max stack size is 2048).
 //    The number of registers saved is encoded in UNWIND_X86_64_FRAMELESS_STACK_REG_COUNT.
 //    UNWIND_X86_64_FRAMELESS_STACK_REG_PERMUTATION contains which registers were
 //    saved and their order.
 // UNWIND_X86_64_MODE_STACK_IND:
 //    A "frameless" (RBP not used as frame pointer) function large constant
 //    stack size.  This case is like the previous, except the stack size is too
 //    large to encode in the compact unwind encoding.  Instead it requires that
 //    the function contains "subq $nnnnnnnn,RSP" in its prolog.  The compact
 //    encoding contains the offset to the nnnnnnnn value in the function in
 //    UNWIND_X86_64_FRAMELESS_STACK_SIZE.
 // UNWIND_X86_64_MODE_DWARF:
 //    No compact unwind encoding is available.  Instead the low 24-bits of the
 //    compact encoding is the offset of the DWARF FDE in the __eh_frame section.
 //    This mode is never used in object files.  It is only generated by the
 //    linker in final linked images which have only DWARF unwind info for a
 //    function.
 //
 
 
 // ARM64
 //
 // 1-bit: start
 // 1-bit: has lsda
 // 2-bit: personality index
 //
 // 4-bits: 4=frame-based, 3=DWARF, 2=frameless
 //  frameless:
 //        12-bits of stack size
 //  frame-based:
 //        4-bits D reg pairs saved
 //        5-bits X reg pairs saved
 //  DWARF:
 //        24-bits offset of DWARF FDE in __eh_frame section
 //
 enum {
     UNWIND_ARM64_MODE_MASK                     = 0x0F000000,
     UNWIND_ARM64_MODE_FRAMELESS                = 0x02000000,
     UNWIND_ARM64_MODE_DWARF                    = 0x03000000,
     UNWIND_ARM64_MODE_FRAME                    = 0x04000000,
 
     UNWIND_ARM64_FRAME_X19_X20_PAIR            = 0x00000001,
     UNWIND_ARM64_FRAME_X21_X22_PAIR            = 0x00000002,
     UNWIND_ARM64_FRAME_X23_X24_PAIR            = 0x00000004,
     UNWIND_ARM64_FRAME_X25_X26_PAIR            = 0x00000008,
     UNWIND_ARM64_FRAME_X27_X28_PAIR            = 0x00000010,
     UNWIND_ARM64_FRAME_D8_D9_PAIR              = 0x00000100,
     UNWIND_ARM64_FRAME_D10_D11_PAIR            = 0x00000200,
     UNWIND_ARM64_FRAME_D12_D13_PAIR            = 0x00000400,
     UNWIND_ARM64_FRAME_D14_D15_PAIR            = 0x00000800,
 
     UNWIND_ARM64_FRAMELESS_STACK_SIZE_MASK     = 0x00FFF000,
     UNWIND_ARM64_DWARF_SECTION_OFFSET          = 0x00FFFFFF,
 };
 // For arm64 there are three modes for the compact unwind encoding:
 // UNWIND_ARM64_MODE_FRAME:
 //    This is a standard arm64 prolog where FP/LR are immediately pushed on the
 //    stack, then SP is copied to FP. If there are any non-volatile registers
 //    saved, then are copied into the stack frame in pairs in a contiguous
 //    range right below the saved FP/LR pair.  Any subset of the five X pairs
 //    and four D pairs can be saved, but the memory layout must be in register
 //    number order.
 // UNWIND_ARM64_MODE_FRAMELESS:
 //    A "frameless" leaf function, where FP/LR are not saved. The return address
 //    remains in LR throughout the function. If any non-volatile registers
 //    are saved, they must be pushed onto the stack before any stack space is
 //    allocated for local variables.  The stack sized (including any saved
 //    non-volatile registers) divided by 16 is encoded in the bits
 //    UNWIND_ARM64_FRAMELESS_STACK_SIZE_MASK.
 // UNWIND_ARM64_MODE_DWARF:
 //    No compact unwind encoding is available.  Instead the low 24-bits of the
 //    compact encoding is the offset of the DWARF FDE in the __eh_frame section.
 //    This mode is never used in object files.  It is only generated by the
 //    linker in final linked images which have only DWARF unwind info for a
 //    function.
 //
 
 
 
 
 
 ////////////////////////////////////////////////////////////////////////////////
 //
 //  Relocatable Object Files: __LD,__compact_unwind
 //
 ////////////////////////////////////////////////////////////////////////////////
 
 //
 // A compiler can generated compact unwind information for a function by adding
 // a "row" to the __LD,__compact_unwind section.  This section has the
 // S_ATTR_DEBUG bit set, so the section will be ignored by older linkers.
 // It is removed by the new linker, so never ends up in final executables.
 // This section is a table, initially with one row per function (that needs
 // unwind info).  The table columns and some conceptual entries are:
 //
 //     range-start               pointer to start of function/range
 //     range-length
 //     compact-unwind-encoding   32-bit encoding
 //     personality-function      or zero if no personality function
 //     lsda                      or zero if no LSDA data
 //
 // The length and encoding fields are 32-bits.  The other are all pointer sized.
 //
 // In x86_64 assembly, these entry would look like:
 //
 //     .section __LD,__compact_unwind,regular,debug
 //
 //     #compact unwind for _foo
 //     .quad    _foo
 //     .set     L1,LfooEnd-_foo
 //     .long    L1
 //     .long    0x01010001
 //     .quad    0
 //     .quad    0
 //
 //     #compact unwind for _bar
 //     .quad    _bar
 //     .set     L2,LbarEnd-_bar
 //     .long    L2
 //     .long    0x01020011
 //     .quad    __gxx_personality
 //     .quad    except_tab1
 //
 //
 // Notes: There is no need for any labels in the __compact_unwind section.
 //        The use of the .set directive is to force the evaluation of the
 //        range-length at assembly time, instead of generating relocations.
 //
 // To support future compiler optimizations where which non-volatile registers
 // are saved changes within a function (e.g. delay saving non-volatiles until
 // necessary), there can by multiple lines in the __compact_unwind table for one
 // function, each with a different (non-overlapping) range and each with
 // different compact unwind encodings that correspond to the non-volatiles
 // saved at that range of the function.
 //
 // If a particular function is so wacky that there is no compact unwind way
 // to encode it, then the compiler can emit traditional DWARF unwind info.
 // The runtime will use which ever is available.
 //
 // Runtime support for compact unwind encodings are only available on 10.6
 // and later.  So, the compiler should not generate it when targeting pre-10.6.
 
 
 
 
 ////////////////////////////////////////////////////////////////////////////////
 //
 //  Final Linked Images: __TEXT,__unwind_info
 //
 ////////////////////////////////////////////////////////////////////////////////
 
 //
 // The __TEXT,__unwind_info section is laid out for an efficient two level lookup.
 // The header of the section contains a coarse index that maps function address
 // to the page (4096 byte block) containing the unwind info for that function.
 //
 
 #define UNWIND_SECTION_VERSION 1
 struct unwind_info_section_header
 {
     uint32_t    version;            // UNWIND_SECTION_VERSION
     uint32_t    commonEncodingsArraySectionOffset;
     uint32_t    commonEncodingsArrayCount;
     uint32_t    personalityArraySectionOffset;
     uint32_t    personalityArrayCount;
     uint32_t    indexSectionOffset;
     uint32_t    indexCount;
     // compact_unwind_encoding_t[]
     // uint32_t personalities[]
     // unwind_info_section_header_index_entry[]
     // unwind_info_section_header_lsda_index_entry[]
 };
 
 struct unwind_info_section_header_index_entry
 {
     uint32_t        functionOffset;
     uint32_t        secondLevelPagesSectionOffset;  // section offset to start of regular or compress page
     uint32_t        lsdaIndexArraySectionOffset;    // section offset to start of lsda_index array for this range
 };
 
 struct unwind_info_section_header_lsda_index_entry
 {
     uint32_t        functionOffset;
     uint32_t        lsdaOffset;
 };
 
 //
 // There are two kinds of second level index pages: regular and compressed.
 // A compressed page can hold up to 1021 entries, but it cannot be used
 // if too many different encoding types are used.  The regular page holds
 // 511 entries.
 //
 
 struct unwind_info_regular_second_level_entry
 {
     uint32_t                    functionOffset;
     compact_unwind_encoding_t    encoding;
 };
 
 #define UNWIND_SECOND_LEVEL_REGULAR 2
 struct unwind_info_regular_second_level_page_header
 {
     uint32_t    kind;    // UNWIND_SECOND_LEVEL_REGULAR
     uint16_t    entryPageOffset;
     uint16_t    entryCount;
     // entry array
 };
 
 #define UNWIND_SECOND_LEVEL_COMPRESSED 3
 struct unwind_info_compressed_second_level_page_header
 {
     uint32_t    kind;    // UNWIND_SECOND_LEVEL_COMPRESSED
     uint16_t    entryPageOffset;
     uint16_t    entryCount;
     uint16_t    encodingsPageOffset;
     uint16_t    encodingsCount;
     // 32-bit entry array
     // encodings array
 };
 
 #define UNWIND_INFO_COMPRESSED_ENTRY_FUNC_OFFSET(entry)            (entry & 0x00FFFFFF)
 #define UNWIND_INFO_COMPRESSED_ENTRY_ENCODING_INDEX(entry)        ((entry >> 24) & 0xFF)
 
 
 
 #endif
 

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