From 43dfe54ce017c8d37eaec480a2f13a492bbc4203 Mon Sep 17 00:00:00 2001 From: serge-sans-paille Date: Thu, 25 Feb 2021 14:24:14 +0100 Subject: [PATCH 2/2] [PATCH][lld] Import compact_unwind_encoding.h from libunwind This avoids an implicit cross package dependency --- lld/include/mach-o/compact_unwind_encoding.h | 477 +++++++++++++++++++++++++++ 1 file changed, 477 insertions(+) create mode 100644 lld/include/mach-o/compact_unwind_encoding.h diff --git a/lld/include/mach-o/compact_unwind_encoding.h b/lld/include/mach-o/compact_unwind_encoding.h new file mode 100644 index 0000000..5301b10 --- /dev/null +++ b/lld/include/mach-o/compact_unwind_encoding.h @@ -0,0 +1,477 @@ +//===------------------ mach-o/compact_unwind_encoding.h ------------------===// +// +// 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 + +// +// 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 + -- 1.8.3.1