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Text of the page (random words):
ample the utilities in simeon cran s emulator myz80 start with the opcode sequence ebh 52h ebh 16 17 an 8086 sees this as a jump and reads its next instruction from offset 154h whereas an 8080 or compatible processor goes straight through and reads its next instruction from 103h a similar sequence used for this purpose is ebh 03h c3h 18 19 john c elliott s fatbin 20 21 22 is a utility to combine a cp m 80 and a dos com file into one executable 16 23 his derivative of the original pmsfx modifies archives created by yoshihiko mino s pmarc to be self extractable under both cp m 80 and dos starting with ebh 18h 2dh 70h 6dh 73h 2dh to also include the pms signature for self extracting pma archives 24 16 23 17 thereby also representing a form of executable ascii code another method to keep a dos compatible operating system from erroneously executing com programs for cp m 80 and msx dos machines 14 is to start the 8080 code with c3h 03h 01h which is decoded as a ret instruction by x86 processors thereby gracefully exiting the program nb 2 while it will be decoded as jp 103h instruction by 8080 processors and simply jump to the next instruction in the program similar the cp m assembler z80asm by slr systems would display an error message when erroneously run on dos 16 some cp m 80 3 0 com files may have one or more rsx overlays attached to them by gencom 25 if so they start with an extra 256 byte header one page in order to indicate this the first byte in the header is set to magic byte c9h which works both as a signature identifying this type of com file to the cp m 3 0 executable loader as well as a ret instruction for 8080 compatible processors which leads to a graceful exit if the file is executed under older versions of cp m 80 nb 2 c9h is never appropriate as the first byte of a program for any x86 processor it has different meanings for different generations nb 3 but is never a meaningful first byte the executable loader in some versions of dos rejects com files that start with c9h avoiding incorrect operation similar overlapping code sequences have also been devised for combined z80 6502 16 8086 68000 16 or x86 mips arm binaries 15 combined binaries for cp m 86 and dos edit cp m 86 and dos do not share a common file extension for executables nb 1 thus it is not normally possible to confuse executables however early versions of dos had so much in common with cp m in terms of its architecture that some early dos programs were developed to share binaries containing executable code one program known to do this was wordstar 3 2x which used identical overlay files in their ports for cp m 86 and ms dos 26 and used dynamically fixed up code to adapt to the differing calling conventions of these operating systems at runtime 26 digital research s gsx for cp m 86 and dos also shares binary identical 16 bit drivers 27 combined com and sys files edit dos device drivers typically with file extension sys start with a file header whose first four bytes are ffffffffh by convention although this is not a requirement 28 this is fixed up dynamically by the operating system when the driver loads typically in the dos bios when it executes device statements in config sys since dos does not reject files with a com extension to be loaded per device and does not test for ffffffffh it is possible to combine a com program and a device driver into the same file 29 28 by placing a jump instruction to the entry point of the embedded com program within the first four bytes of the file three bytes are usually sufficient 28 if the embedded program and the device driver sections share a common portion of code or data it is necessary for the code to deal with being loaded at offset 0100h as a com style program and at 0000h as a device driver 29 for shared code loaded at the wrong offset but not designed to be position independent this requires an internal address fix up 29 similar to what would otherwise already have been carried out by a relocating loader except for that in this case it has to be done by the loaded program itself this is similar to the situation with self relocating drivers but with the program already loaded at the target location by the operating system s loader crash protected system files edit under dos some files by convention have file extensions which do not reflect their actual file type nb 4 for example country sys 30 is not a dos device driver nb 5 but a binary nls database file for use with the config sys country directive and the nlsfunc driver 30 the pc dos and dr dos system files ibmbio com and ibmdos com are special binary images loaded by bootstrap loaders not com style programs nb 5 trying to load country sys with a device statement or executing ibmbio com or ibmdos com at the command prompt will cause unpredictable results nb 4 nb 6 it is sometimes possible to avoid this by utilizing techniques similar to those described above for example dr dos 7 02 and higher incorporate a safety feature developed by matthias r paul 31 if these files are called inappropriately tiny embedded stubs will just display some file version information and exit gracefully 32 31 33 30 additionally the message is specifically crafted to follow certain magic patterns recognized by the external netware dr dos version file identification utility 30 31 nb 7 a similar protection feature was the 8080 instruction c7h rst 0 at the very start of jay sage s and joe wright s z system type 3 and type 4 z3env programs 34 35 as well as z3txt language overlay files 36 which would result in a warm boot instead of a crash under cp m 80 if loaded inappropriately 34 35 36 nb 2 in a distantly similar fashion many binary file formats by convention include a 1ah byte ascii z near the beginning of the file this control character will be interpreted as soft end of file eof marker when a file is opened in non binary mode and thus under many operating systems including the pdp 6 monitor 37 and rt 11 vms tops 10 38 cp m 39 40 dos 41 and windows 42 it prevents binary garbage from being displayed when a file is accidentally printed at the console linux edit fatelf universal binaries for linux edit fatelf logo fatelf 43 was a fat binary implementation for linux and other unix like operating systems technically a fatelf binary was a concatenation of elf binaries with some meta data indicating which binary to use on what architecture 44 additionally to the cpu architecture abstraction byte order word size cpu instruction set etc there is the advantage of binaries with support for multiple kernel abis and versions fatelf has several use cases according to developers 43 distributions no longer need to have separate downloads for various platforms separated lib lib32 and lib64 trees are not required anymore in os directory structure the correct binary and libraries are centrally chosen by the system instead of shell scripts if the elf abi changes someday legacy users can be still supported distribution of web browser plug ins that work out of the box with multiple platforms distribution of one application file that works across linux and bsd os variants without a platform compatibility layer on them one hard drive partition can be booted on different machines with different cpu architectures for development and experimentation same root file system different kernel and cpu architecture applications provided by network share or usb sticks will work on multiple systems this is also helpful for creating portable applications and also cloud computing images for heterogeneous systems 45 a proof of concept ubuntu 9 04 image is available 46 as of 2021 update fatelf has not been integrated into the mainline linux kernel citation needed 47 48 windows edit fatpack edit although the portable executable format used by windows does not allow assigning code to platforms it is still possible to make a loader program that dispatches based on architecture this is because desktop versions of windows on arm have support for 32 bit x86 emulation making it a useful universal machine code target fatpack is a loader that demonstrates the concept it includes a 32 bit x86 program that tries to run the executables packed into its resource sections one by one 49 similar concepts edit the following approaches are similar to fat binaries in that multiple versions of machine code of the same purpose are provided in the same file heterogeneous computing edit since 2007 some specialized compilers for heterogeneous platforms produce code files for parallel execution on multiple types of processors i e the chi c for heterogeneous integration compiler from the intel exochi exoskeleton sequencer development suite extends the openmp pragma concept for multithreading to produce fat binaries containing code sections for different instruction set architectures isas from which the runtime loader can dynamically initiate the parallel execution on multiple available cpu and gpu cores in a heterogeneous system environment 50 51 introduced in february 2007 nvidia s parallel computing platform cuda compute unified device architecture is a software to enable general purpose computing on gpus gpgpu its llvm based compiler nvcc can create elf based fat binaries containing so called ptx virtual assembly as text which the cuda runtime driver can later just in time compile into some sass streaming assembler binary executable code for the actually present target gpu the executables can also include so called cuda binaries aka cubin files containing dedicated executable code sections for one or more specific gpu architectures from which the cuda runtime can choose from at load time 52 53 54 55 56 57 fat binaries are also supported by gpgpu sim de a gpu simulator introduced in 2007 as well 58 59 multi2sim m2s an opencl heterogeneous system simulator framework originally only for either mips or x86 cpus but later extended to also support arm cpus and gpus like the amd ati evergreen southern islands as well as nvidia fermi kepler families 60 supports elf based fat binaries as well 61 60 fat objects edit gnu compiler collection gcc and llvm do not have a fat binary format but they do have fat object files for link time optimization lto since lto involves delaying the compilation to link time the object files must store the intermediate representation ir but on the other hand machine code may need to be stored too for speed or compatibility an lto object containing both ir and machine code is known as a fat object 62 function multi versioning edit even in a program or library intended for the same instruction set architecture a programmer may wish to make use of some newer instruction set extensions while keeping compatibility with an older cpu this can be achieved with function multi versioning fmv versions of the same function are written into the program and a piece of code decides which one to use by detecting the cpu s capabilities such as through cpuid intel c compiler gcc and llvm all have the ability to automatically generate multi versioned functions 63 this is a form of dynamic dispatch without any semantic effects many math libraries feature hand written assembly routines that are automatically chosen according to cpu capability examples include glibc intel mkl and openblas in addition the library loader in glibc supports loading from alternative paths for specific cpu features 64 a similar but byte level granular approach originally devised by matthias r paul and axel c frinke is to let a small self discarding relaxing and relocating loader embedded into the executable file alongside any number of alternative binary code snippets conditionally build a size or speed optimized runtime image of a program or driver necessary to perform or not perform a particular function in a particular target environment at load time through a form of dynamic dead code elimination ddce 65 66 67 68 see also edit cross platform software dos stub fat pointer linear executable lx new executable ne portable executable pe position independent code pic side effect universal hex format a fat hex file format targeting multiple platforms alphanumeric executable executable code camouflaged as sometimes even readable text multi architecture shellcode shellcode targeting multiple platforms and sometimes even camouflaged as alphanumeric text notes edit a b this isn t a problem for cp m 86 style executables under cp m 86 cp m 86 plus personal cp m 86 s5 dos concurrent cp m 86 concurrent dos concurrent dos 286 flexos concurrent dos 386 dos plus multiuser dos system manager and real 32 because they use the file extension cmd rather than com for these files the cmd extension however is conflictive with the file extension for batchjobs written for the command line processor cmd exe under the os 2 and windows nt operating system families a b c this works because a suitable return instruction can be used to exit programs under cp m 80 cp m 86 and dos although the opcodes exact conditions and underlying mechanisms differ under cp m 80 programs can terminate that is warm boot into the bios by jumping to 0 in the zero page either directly with rst 0 8080 8085 z80 opcode c7h or by calling bdos function 0 through the call 5 interface alternatively as the stack is prepared to hold a 0 return address before passing control to a loaded program they can for as long as the stack is aligned also be exited by issuing a ret opcode c9h instruction thereby falling into the terminating code at offset 0 in the zero page although dos has a dedicated int 20h interrupt as well as int 21h api sub functions to terminate programs which are preferable for more complicated programs for machine translated programs dos also emulates cp m s behaviour to some extent a program can terminate itself by jumping to offset 0 in its psp the equivalent to cp m s zero page where the system had previously planted an int 20h instruction also a loaded program s initial stack is prepared to hold a word of 0 so that a program issuing a near return retn 8088 8086 opcode c3h will implicitly jump to the start of its code segment as well thereby eventually reaching the int 20h as well a in cp m 86 the zero page is structured differently and there is no call 5 interface but the stack return method and bdos function 0 but now through int e0h both work as well on 8088 8086 processors the opcode c9h is an undocumented alias for cbh retf popping cs ip from the stack whereas it decodes as leave set sp to bp and pop bp on 80188 80186 and newer processors a b this problem could have been avoided by choosing non conflicting file extensions but once introduced these particular file names were retained from very early versions of ms dos pc dos for compatibility reasons with third party tools hard wired to expect these specific file names a b other dos files of this type are keyboard sys a binary keyboard layout database file for the keyboard driver keyb under ms dos and pc dos io sys containing the dos bios under...