diff options
Diffstat (limited to '05/README.md')
| -rw-r--r-- | 05/README.md | 19 |
1 files changed, 11 insertions, 8 deletions
diff --git a/05/README.md b/05/README.md index a68cbbb..13af044 100644 --- a/05/README.md +++ b/05/README.md @@ -213,7 +213,8 @@ static unsigned char __syscall_data[] = { }; #define __syscall(no, arg1, arg2, arg3, arg4, arg5, arg6)\ - (((unsigned long (*)(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long))__syscall_data)\ + (((unsigned long (*)(unsigned long, unsigned long, unsigned long,\ + unsigned long, unsigned long, unsigned long, unsigned long))__syscall_data)\ (no, arg1, arg2, arg3, arg4, arg5, arg6)) ``` @@ -296,6 +297,8 @@ Oh wait, tcc uses it. Fortunately it's not critically important to tcc. - `mktime()` always fails. - The keywords `signed`, `volatile`, `register`, and `const` are all ignored, but this should almost never have an effect on a legal C program. +- Converting `unsigned long` to `double`/`float` treats the number as signed (this is incorrect +for `unsigned long` values above 2<sup>63</sup>). ## anecdotes @@ -306,7 +309,7 @@ which happened along the way: doesn't have floats turned out to be quite a fun challenge! Not all decimal numbers have a perfect floating point representation. You could round 0.1 up to ~0.1000000000000000056, or down to ~0.0999999999999999917. -This stage's C compiler should be entirely correct, up to rounding (which is all that the +This stage's C compiler should be correct up to rounding (which is all that the C standard requires). But typically C compilers will round to whichever is closest to the decimal value. Implementing this correctly @@ -343,7 +346,7 @@ executable from the gcc one. After spending a long time looking at disassemblies tcc_define_symbol(s, "__linux", NULL); # endif ``` -If the `__linux__` macro is defined (to indicate that the target OS is linux), +If the `__linux__` macro is defined (to indicate that the OS is linux), tcc will also define the `__linux__` macro in any programs it compiles. Unlike gcc, our compiler doesn't define the `__linux__` macro, so when it's used to compile tcc, tcc won't define it either, no matter how many times you compile it @@ -424,7 +427,7 @@ get to glibc: - build & install dash - build & install sed-4.2 - build & install ld, as (from binutils) -- build gcc +- build & install gcc - build & install grep-3.7 - build & install awk - build & install bash @@ -438,10 +441,10 @@ This made broken Makefiles which I spent hours editing by hand -- and is it really compiled from scratch if it's built from computer-generated source files and Makefiles? And although the developers at GNU -refrain from declaring variables after statements, and keep old-style function declarations -to support compilers from the 80s; they *still* manage to use gcc-specific extensions, and -not even extensions that all versions of gcc support! +refrain from declaring variables after statements, +they can't help but use bizarre gcc-specific extensions. After hours and hours of fixing compiler errors, I decided to give up. -THIS WAY LIES MADNESS. +I'll just say, as a reminder to my future self, and a warning to anyone +else who wants to compile glibc from scratch: THIS WAY LIES MADNESS. |