satrt readme

05/README.md

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+# [bootstrap](../README.md) stage 05
+
+This stage consists of a C compiler capable of compiling TCC (after some modifications
+to TCC's source code).
+Run
+
+```
+make
+```
+
+to build our C compiler and TCC. This will take some time (approx. 25 seconds on my computer).
+A test program, `test.out` will be compiled using `tcc`. If you run
+it, you should get the output
+
+```
+Hello, world!
+```
+
+So now we just compile TCC with itself, and we're done, right?
+Well, not quite...
+
+## the nightmare begins
+
+The issue here is that to compile TCC/GCC with TCC, we need libc, the C standard library functions.
+Our C compiler just includes these functions in the standard header files, but normally
+the code for them is located in a separate library file (called something like
+`/usr/lib/x86_64-linux-gnu/libc-2.31.so`).
+
+This library file is itself compiled from C source files (typically glibc).
+So, can't we just compile glibc with TCC, then compile TCC with itself?
+Well, no. Compiling glibc with TCC is basically impossible; you need to compile
+it with GCC.
+
+Other libc implementations aren't too happy about TCC either -- I tried to compile
+[musl](http://www.musl-libc.org/) for several hours, and had to give up in the end.
+
+It seems that the one option left is to make our own libc, and try to use it along with
+TCC to compile GCC.
+From there, we should be able to compile glibc with GCC. Then, we can compile GCC with GCC and glibc.
+If we do all this, we should get the same libc.so and gcc files as if we had started
+with any GCC and glibc builds. It's all very confusing.
+