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diff --git a/miniany/README b/miniany/README index 6367011..814f6b3 100644 --- a/miniany/README +++ b/miniany/README @@ -1,85 +1,113 @@ -# Running on host: -``` -./build.sh cc tcc hosted d -./build.sh cc tcc freestanding d -./cc < test1.c > test1.asm -fasm test1.asm test1.bin -ndisasm -b32 -o1000000h -a test1.bin -``` +# CC - a self-hosting, bootstrappable, minimal C compiler -# Running on c4: +## Introduction -``` -echo -n -e "\034" > EOF +On the never-ending quest of a minimal system I found Swieros and C4 (the C compiler in 4 functions). Inspired and intrigued I started to implement my own. + +For abaos (a small operating system of mine, also in C) I cloned the minimal C library, so we can build a freestanding version of C4. + +C4 serves as a test whether my own CC is minimal enough and doesn't use silly functions. Additionally C4 as well as CC are compiled both in a (on Linux) hosted version and a freestanding version. We use a series of compilers like gcc, clang, tcc and pcc to make sure that we are not using silly C constructs. + +In order to be able to port easily we make almost no use of system calls, the ones we need are: + + +- brk: for malloc/free, change the start address of the heap segment of the process, if the OS only assigns a single static space, then brk results in a NOP. +- exit: terminate the process, return does not always work in all combinations (for instance with pcc on Linux). Can be a NOP, we don't require any trickery as <i>atext </i>and we don't use buffering anywhere (for instance flushing stdout on exit). +- read/write: read from stdin linearly, write to stdout linearly, this is essentially a model using an input and an output tape. Those two functions must really exist. This basically eliminates the need for a file system which we might not have during early bootstrapping. + +Similarly we simplify the C language to not use certain features which can cause trouble when bootstrapping: + + +- variable arguments: though simple in principle (just some pointers into the stack if you use a stack for function parameters), it is not typesafe. And the only example in practice it's really heavily used for is in printf-like functions. +- preprocessor: it needs a filesystem, we take this outside of the compiler by feeding it an (eventually) concatenated list of \*.c files. +- two types: int and char, so we can interpret memory as words or as bytes. + +## Local version of C4 + +The local version of C4 has the following adaoptions and extensions: + + +- switch statement from the <i>switch-and-struct</i>s branch, adapted c4 itself to use switch statements instead of if's (as in the <i>switch-and-structs </i>branch) +- struct support from <i>switch-and-structs</i> +- constants like <i>EO</i>F, <i>EXIT\_SUCCES</i>S, <i>NUL</i>L +- standard C block comments along to c++ end of line ones +- negative enum initializers +- do/while loops +- more C functions like <i>isspac</i>e, <i>get</i>c, <i>strcm</i>p +- some simplified functions for printing like <i>putstring</i>, <i>putin</i>t, <i>putn</i>l +- strict C89 conformance, mainly use standard comment blocks, also removed some warnings +- some casts around malloc and memset to fit to non-void freestanding-libc +- converted printf to putstring/putint/putnl and some helper functions for error reporting like error() +- removed all memory leaks +- de-POSIX-ified, no open/read/close, use getchar from stdin only (don't assume the existence of a file system), this also means we had to create sort of an old style tape-file with FS markers to separate the files piped to c4. + +<i>Note: </i>only too late I discovered that there was a C5 version of the same compiler, which would maybe have served better as a basis. + +## Examples + +### Running on the host system using the hosts C compiler + +Compiled in either hosted (host libc) or freestanding (our own libc, currently IA-32 Linux kernel only syscalls): + +`./build.sh cc hostcc hosted d +./build.sh cc hostcc freestanding d +./cc \< test1.c \> test1.asm` +Create a plain binary from the assembly code: + +`fasm test1.asm test1.bin` +Disassemble it to verify it's correctness: + +`ndisasm -b32 -o1000000h -a test1.bin` +You can choose <i>gcc</i>, <i>clang</i>, <i>tcc </i>or <i>pcc </i>as host compiler (<i>hostcc</i>). + +### Running on the host in the C4 interpreter + +Running in C4 interpreter, again, the C4 program can be compiled in hosted or freestanding mode: + +`./build.sh c4 hostcc hosted d +./build.sh c4 hostcc freestanding d` +Here again you can choose the host compiler for compiling C4. + +Then we have to create the standard input for C4 using: + +`echo -n -e "\034" \> EOF cat cc.c EOF hello.c | ./c4 cat c4.c EOF cc.c EOF hello.c | ./c4 -cat c4.c4 EOF c4.c EOF cc.c EOF hello.c | ./c4 -``` - -# Local version of c4 - -This local version of c4 is used to guarantee that our own bootstrapped -cc.c can also run on c4. This makes sure we are not integrating too -complex things into our own compiler. - -* currently integrated: - - switch statement from switch-and-structs, adapted c4 to use switch - statements instead of ifs (as in switch-and-structs) - - structures from switch-and-structs -* my own changes: - - constants like EOF, EXIT_SUCCESS, NULL - - standard C block comments along to c++ end of line ones - - negative enum initializers - - do/while loops - - more C functions like isspace, getc, strcmp - - some simplified functions for printing like putstring, putint, putnl - - strict C89 conformance, mainly use standard comment blocks, also - removed some warnings - - some casts around malloc and memset to fit to non-void freestanding-libc - - converted printf to putstring/putint/putnl and some helper functions - for error reporting like error() - - removed memory leaks - - de-POSIX-ified, no open/read/close, use getchar from stdin only - (don't assume the existence of a file system), this also means - we have to create sort of an old style tape-file with FS markers - to separate the files piped to c4. - -# Acknoledgments and references - -* c4 - * https://github.com/rswier/c4.git - c4 - C in four functions - minimalistic C compiler running on an emulator on the IR, inspiration - for this project - * https://github.com/rswier/c4/blob/switch-and-structs/c4.c: - c4 adaptions to provide switch and structs - * https://github.com/EarlGray/c4: a X86 JIT version of c4 - * https://github.com/jserv/amacc: based on C4, JIT or native code, for - ARM, quite well documented, also very nice list of compiler - resources on Github page - -* selfie - * http://selfie.cs.uni-salzburg.at/: - C* self-hosting C compiler (also emulator, hypervisor) for RISCV, - inspiration for what makes up a minimal C language - -* tiny.c - * http://www.iro.umontreal.ca/~felipe/IFT2030-Automne2002/Complements/tinyc.c, - Marc Feeley, really easy and much more readable, meant as educational compiler - -* c.c in swieros: https://github.com/rswier/swieros.git - -* https://github.com/lotabout/write-a-C-interpreter/blob/master/tutorial/en/: tutorial - based on C4 how to build a C interpreter, explains nicely details in C4. - -* https://github.com/felipensp/assembly/blob/master/x86/itoa.s, - https://baptiste-wicht.com/posts/2011/11/print-strings-integers-intel-assembly.html, - putint for early debugging - -* documentation - * "Compiler Construction", Niklaus Wirth - * https://github.com/DoctorWkt/acwj: a nice series on building a C compiler, - step by step with lots of good explanations - * https://www.engr.mun.ca/~theo/Misc/exp_parsing.htm#climbing, - https://en.wikipedia.org/wiki/Operator-precedence_parser#Precedence_climbing_method +cat c4.c4 EOF c4.c EOF cc.c EOF hello.c | ./c4` +EOF contains the traditional FS (file separator) character in the ASCII character set. Every time c4/c4.c is invoked it reads exacly one input file up to the first FS character (or stops at the end of stdin). + +We can also use <i>-s</i>, or <i>-d </i>on every level as follows: + +`cat cc.c EOF hello.c | ./c4 -d` +## References + +Compiler construction in general: + + +- <i>"Compiler </i><i>Construction"</i>", Niklaus Wirth +- https://github.com/DoctorWkt/acwj: a nice series on building a C compiler, step by step with lots of good explanations +- https://www.engr.mun.ca/~theo/Misc/exp\_parsing.htm\#climbing, https://en.wikipedia.org/wiki/Operator-precedence\_parser\#Precedence\_climbing\_method +- https://github.com/lotabout/write-a-C-interpreter/blob/master/tutorial/en/, tutorial based on C4 how to build a C interpreter, explains nicely details in C4. + +C4: + + +- https://github.com/rswier/c4.git, <i>C4 </i><i>- </i><i>C </i><i>in </i><i>four </i><i>functions</i>, Robert Swierczek, minimalistic C compiler running on an emulator on the IR, inspiration for this project +- https://github.com/rswier/c4/blob/switch-and-structs/c4.c, c4 adaptions to provide switch and structs +- https://github.com/EarlGray/c4: a X86 JIT version of c4 +- https://github.com/jserv/amacc: based on C4, JIT or native code, for ARM, quite well documented, also very nice list of compiler resources on Github page + +Other minimal compilers and systems: + + +- http://selfie.cs.uni-salzburg.at/: C\* self-hosting C compiler (also emulator, hypervisor) for RISCV, inspiration for what makes up a minimal C language +- http://www.iro.umontreal.ca/~felipe/IFT2030-Automne2002/Complements/tinyc.c, Marc Feeley, really easy and much more readable, meant as educational compiler +- https://github.com/rswier/swieros.git: c.c in swieros, Robert Swierczek + +Assembly: + + +- https://github.com/felipensp/assembly/blob/master/x86/itoa.s, for putint (early debugging keyword) +- https://baptiste-wicht.com/posts/2011/11/print-strings-integers-intel-assembly.htm (earldy debugging keyword) + |