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+//===------------------ mach-o/compact_unwind_encoding.h ------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//
+// 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 endoding 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 constains 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 constains 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 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
+