mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Mu - 030---translate.cc</title> <meta name="Generator" content="Vim/8.1"> <meta name="plugin-version" content="vim8.1_v1"> <meta name="syntax" content="cpp"> <meta name="settings" content="number_lines,use_css,pre_wrap,no_foldcolumn,expand_tabs,line_ids,prevent_copy="> <meta name="colorscheme" content="minimal-light"> <style type="text/css">  </style> <script type='text/javascript'>  </script> </head> <body onload='JumpToLine();'> <a href='https://github.com/akkartik/mu/blob/master/030---translate.cc'>https://github.com/akkartik/mu/blob/master/030---translate.cc</a> <pre id='vimCodeElement'> 1 //: After that lengthy prelude to define an x86 emulator, we are now ready to 2 //: start translating SubX notation. 3 4 //: Translator workflow: read 'source' file. Run a series of transforms on it, 5 //: each passing through what it doesn't understand. The final program should 6 //: be just machine code, suitable to emulate, or to write to an ELF binary. 7 8 :(before "End Main") 9 if (<a href='001help.cc.html#L102'>is_equal</a>(argv[1], "translate")) { 10 // Outside of tests, traces must be explicitly requested. 11 if (<a href='003trace.cc.html#L448'>Trace_file</a>.is_open()) <a href='003trace.cc.html#L72'>Trace_stream</a> = new trace_stream; 12 <a href='000organization.cc.html#L150'>reset</a>(); 13 // Begin bootstrap translate 14 program p; 15 string output_filename; 16 for (int i = /*skip 'bootstrap translate'*/2; i < argc; ++i) { 17 if (<a href='001help.cc.html#L102'>is_equal</a>(argv[i], "-o")) { 18 ++i; 19 if (i >= argc) { 20 <a href='030---translate.cc.html#L65'>print_translate_usage</a>(); 21 cerr << "'-o' must be followed by a filename to write results to\n"; 22 exit(1); 23 } 24 output_filename = argv[i]; 25 } 26 else { 27 <a href='003trace.cc.html#L96'>trace</a>(2, "parse") << argv[i] << end(); 28 ifstream fin(argv[i]); 29 if (!fin) { 30 cerr << "could not open " << argv[i] << '\n'; 31 return 1; 32 } 33 parse(fin, p); 34 if (<a href='003trace.cc.html#L264'>trace_contains_errors</a>()) return 1; 35 } 36 } 37 if (p.<a href='011run.cc.html#L106'>segments</a>.empty()) { 38 <a href='030---translate.cc.html#L65'>print_translate_usage</a>(); 39 cerr << "nothing to do; must provide at least one file to read\n"; 40 exit(1); 41 } 42 if (output_filename.empty()) { 43 <a href='030---translate.cc.html#L65'>print_translate_usage</a>(); 44 cerr << "must provide a filename to write to using '-o'\n"; 45 exit(1); 46 } 47 <a href='003trace.cc.html#L96'>trace</a>(2, "transform") << "begin" << end(); 48 transform(p); 49 if (<a href='003trace.cc.html#L264'>trace_contains_errors</a>()) return 1; 50 <a href='003trace.cc.html#L96'>trace</a>(2, "translate") << "begin" << end(); 51 save_elf(p, output_filename); 52 if (<a href='003trace.cc.html#L264'>trace_contains_errors</a>()) { 53 unlink(output_filename.c_str()); 54 return 1; 55 } 56 // End bootstrap translate 57 return 0; 58 } 59 60 :(code) 61 void transform(program& p) { 62 // End transform(program& p) 63 } 64 65 void <a href='030---translate.cc.html#L65'>print_translate_usage</a>() { 66 cerr << "Usage: bootstrap translate file1 file2 ... -o output\n"; 67 } 68 69 // write out a program to a bare-bones ELF file 70 void save_elf(const program& p, const string& filename) { 71 ofstream out(filename.c_str(), ios::binary); 72 save_elf(p, out); 73 out.close(); 74 } 75 76 void save_elf(const program& p, ostream& out) { 77 // validation: stay consistent with the self-hosted translator 78 if (p.<a href='011run.cc.html#L105'>entry</a> == 0) { 79 <a href='003trace.cc.html#L228'>raise</a> << "no 'Entry' label found\n" << end(); 80 return; 81 } 82 if (find(p, "data") == NULL) { 83 <a href='003trace.cc.html#L228'>raise</a> << "must include a 'data' segment\n" << end(); 84 return; 85 } 86 // processing 87 <a href='030---translate.cc.html#L92'>write_elf_header</a>(out, p); 88 for (size_t i = 0; i < p.<a href='011run.cc.html#L106'>segments</a>.size(); ++i) 89 <a href='030---translate.cc.html#L188'>write_segment</a>(p.<a href='011run.cc.html#L106'>segments</a>.at(i), out); 90 } 91 92 void <a href='030---translate.cc.html#L92'>write_elf_header</a>(ostream& out, const program& p) { 93 char c = '\0'; 94 #define O(X) c = (X); out.write(&c, sizeof(c)) 95 // host is required to be little-endian 96 #define emit(X) out.write(reinterpret_cast<const char*>(&X), sizeof(X)) 97 //// ehdr 98 // e_ident 99 O(0x7f); O(/*E*/0x45); O(/*L*/0x4c); O(/*F*/0x46); 100 O(0x1); // 32-bit format 101 O(0x1); // little-endian 102 O(0x1); O(0x0); 103 for (size_t i = 0; i < 8; ++i) { O(0x0); } 104 // e_type 105 O(0x02); O(0x00); 106 // e_machine 107 O(0x03); O(0x00); 108 // e_version 109 O(0x01); O(0x00); O(0x00); O(0x00); 110 // e_entry 111 uint32_t e_entry = p.<a href='011run.cc.html#L105'>entry</a>; 112 // Override e_entry 113 emit(e_entry); 114 // e_phoff -- immediately after ELF header 115 uint32_t e_phoff = 0x34; 116 emit(e_phoff); 117 // e_shoff; unused 118 uint32_t dummy32 = 0; 119 emit(dummy32); 120 // e_flags; unused 121 emit(dummy32); 122 // e_ehsize 123 uint16_t e_ehsize = 0x34; 124 emit(e_ehsize); 125 // e_phentsize 126 uint16_t e_phentsize = 0x20; 127 emit(e_phentsize); 128 // e_phnum 129 uint16_t e_phnum = <a href='001help.cc.html#L170'>SIZE</a>(p.<a href='011run.cc.html#L106'>segments</a>); 130 emit(e_phnum); 131 // e_shentsize 132 uint16_t dummy16 = 0x0; 133 emit(dummy16); 134 // e_shnum 135 emit(dummy16); 136 // e_shstrndx 137 emit(dummy16); 138 139 uint32_t p_offset = /*size of ehdr*/0x34 + <a href='001help.cc.html#L170'>SIZE</a>(p.<a href='011run.cc.html#L106'>segments</a>)*0x20/*size of each phdr*/; 140 for (int i = 0; i < <a href='001help.cc.html#L170'>SIZE</a>(p.<a href='011run.cc.html#L106'>segments</a>); ++i) { 141 const segment& curr = p.<a href='011run.cc.html#L106'>segments</a>.at(i); 142 //// phdr 143 // p_type 144 uint32_t p_type = 0x1; 145 emit(p_type); 146 // p_offset 147 emit(p_offset); 148 // p_vaddr 149 uint32_t p_start = curr.start; 150 emit(p_start); 151 // p_paddr 152 emit(p_start); 153 // p_filesz 154 uint32_t size = <a href='030---translate.cc.html#L198'>num_words</a>(curr); 155 assert(p_offset + size < <a href='010---vm.cc.html#L89'>SEGMENT_ALIGNMENT</a>); 156 emit(size); 157 // p_memsz 158 emit(size); 159 // p_flags 160 uint32_t p_flags = (curr.<a href='011run.cc.html#L111'>name</a> == "code") ? /*r-x*/0x5 : /*rw-*/0x6; 161 emit(p_flags); 162 163 // p_align 164 // "As the system creates or augments a process image, it logically copies 165 // a file's segment to a virtual memory segment. When—and if— the system 166 // physically reads the file depends on the program's execution behavior, 167 // system load, and so on. A process does not require a physical page 168 // unless it references the logical page during execution, and processes 169 // commonly leave many pages unreferenced. Therefore delaying physical 170 // reads frequently obviates them, improving system performance. To obtain 171 // this efficiency in practice, executable and shared object files must 172 // have segment images whose file offsets and virtual addresses are 173 // congruent, modulo the page size." -- <a href="http://refspecs.linuxbase.org/elf/elf.pdf">http://refspecs.linuxbase.org/elf/elf.pdf</a> (page 95) 174 uint32_t p_align = 0x1000; // default page size on linux 175 emit(p_align); 176 if (p_offset % p_align != p_start % p_align) { 177 <a href='003trace.cc.html#L228'>raise</a> << "segment starting at 0x" << <a href='010---vm.cc.html#L395'>HEXWORD</a> << p_start << " is improperly aligned; alignment for p_offset " << p_offset << " should be " << (p_offset % p_align) << " but is " << (p_start % p_align) << '\n' << end(); 178 return; 179 } 180 181 // prepare for next segment 182 p_offset += size; 183 } 184 #undef O 185 #undef emit 186 } 187 188 void <a href='030---translate.cc.html#L188'>write_segment</a>(const segment& s, ostream& out) { 189 for (int i = 0; i < <a href='001help.cc.html#L170'>SIZE</a>(s.<a href='011run.cc.html#L113'>lines</a>); ++i) { 190 const vector<word>& w = s.<a href='011run.cc.html#L113'>lines</a>.at(i).<a href='011run.cc.html#L122'>words</a>; 191 for (int j = 0; j < <a href='001help.cc.html#L170'>SIZE</a>(w); ++j) { 192 uint8_t x = <a href='011run.cc.html#L288'>hex_byte</a>(w.at(j).data); // we're done with metadata by this point 193 out.write(reinterpret_cast<const char*>(&x), /*sizeof(byte)*/1); 194 } 195 } 196 } 197 198 uint32_t <a href='030---translate.cc.html#L198'>num_words</a>(const segment& s) { 199 uint32_t sum = 0; 200 for (int i = 0; i < <a href='001help.cc.html#L170'>SIZE</a>(s.<a href='011run.cc.html#L113'>lines</a>); ++i) 201 sum += <a href='001help.cc.html#L170'>SIZE</a>(s.<a href='011run.cc.html#L113'>lines</a>.at(i).<a href='011run.cc.html#L122'>words</a>); 202 return sum; 203 } 204 205 :(before "End Includes") 206 using std::ios; </pre> </body> </html>


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