diff options
Diffstat (limited to 'subx')
| -rw-r--r-- | subx/001help.cc | 4 | ||||
| -rw-r--r-- | subx/010vm.cc | 13 | ||||
| -rw-r--r-- | subx/Readme.md | 4 |
3 files changed, 19 insertions, 2 deletions
diff --git a/subx/001help.cc b/subx/001help.cc index 3b60f60f..c2b0390e 100644 --- a/subx/001help.cc +++ b/subx/001help.cc @@ -54,7 +54,9 @@ void init_help() { "Comments start with the '#' character. It should be at the start of a word (start of line, or following a space).\n" "Each segment starts with a header line: a '--' delimiter followed by the starting address for the segment.\n" "The starting address for a segment has some finicky requirements. But just start with a round number, and `subx` will try to guide you to the right answer.\n" - "Currently only the first segment contains executable code (because it gets annoying to have to change addresses in later segments every time an earlier one changes length).\n" + "A good default is to try to start the first segment at the default address of 0x08048000, and to start subsequent segments at least 0x1000 (most common page size) bytes after.\n" + "If a segment occupies than 0x1000 bytes you'll need to push subsequent segments further down.\n" + "Currently only the first segment contains executable code (because it gets annoying to have to change addresses in later segments every time an earlier one changes length; one of those finicky requirements).\n" "Programming in machine code can be annoying, but let's see if we can make it nice enough to be able to write a compiler in it.\n" ); // End Help Texts diff --git a/subx/010vm.cc b/subx/010vm.cc index 50074114..67c407a8 100644 --- a/subx/010vm.cc +++ b/subx/010vm.cc @@ -27,6 +27,19 @@ uint32_t EIP = 1; // preserve null pointer bzero(Reg, sizeof(Reg)); EIP = 1; // preserve null pointer +:(before "End Help Contents") +cerr << " registers\n"; +:(before "End Help Texts") +put(Help, "registers", + "SubX currently supports 8 integer registers, numbered from 0 to 7.\n" + "There's also a register for the address of the currently executing instruction. It is modified by jumps.\n" + "Various instructions modify one or more of 3 flags, as a side-effect:\n" + "- the sign flag: usually set if an arithmetic result is negative, or reset if not.\n" + "- the zero flag: usually set if a result is zero, or reset if not.\n" + "- the overflow flag: usually set if an arithmetic result overflows.\n" + "We don't support non-integer (floating-point) registers yet.\n" +); + :(before "End Globals") // the subset of x86 flag registers we care about bool SF = false; // sign flag diff --git a/subx/Readme.md b/subx/Readme.md index 77f338ad..854a3876 100644 --- a/subx/Readme.md +++ b/subx/Readme.md @@ -13,7 +13,9 @@ and libc.) check my program for errors rather than to hide low-level details. Force myself to think about security by living with raw machine code for a while. Reintroduce high level languages (HLLs) only after confidence is regained - in the foundations. Delegate only when I can verify with confidence. + in the foundations (and when the foundations are ergonomic enough to + support developing a compiler in them). Delegate only when I can verify + with confidence. 2. The software in our computers has grown incomprehensible. Nobody understands it all, not even experts. Even simple programs written by a |