diff options
Diffstat (limited to '01')
| -rw-r--r-- | 01/Makefile | 2 | ||||
| -rw-r--r-- | 01/README.md | 32 | ||||
| -rw-r--r-- | 01/commands.txt | 5 |
3 files changed, 21 insertions, 18 deletions
diff --git a/01/Makefile b/01/Makefile index 5dde439..f40b401 100644 --- a/01/Makefile +++ b/01/Makefile @@ -5,3 +5,5 @@ out00: in00 ../00/hexcompile %.html: %.md ../markdown ../markdown $< +clean: + rm -f out00 out01 README.html diff --git a/01/README.md b/01/README.md index 5ba8c52..a67d28b 100644 --- a/01/README.md +++ b/01/README.md @@ -8,7 +8,7 @@ is the executable for this stage's compiler. Run it (it'll read from the file `Hello, world!` when run. Let's take a look at the input we're providing to the stage 01 compiler, `in01`: -<pre><code> +``` || ELF Header ;im;01;00;00;00;00;00;00;00 file descriptor for stdout ;JA @@ -24,9 +24,9 @@ stage 01 compiler, `in01`: ;sy ;'H;'e;'l;'l;'o;',;' ;'w;'o;'r;'l;'d;'!;\n the string we're printing ; -</code></pre> +``` -Look at that! There are comments! Much nicer than just hexadecimal digit pairs. +Look at that! There are even comments! Much nicer than just hexadecimal digit pairs. ## end result @@ -50,9 +50,9 @@ actually print out an error message and exit, rather than continuing as if nothing happened! Try adding `xx;` to the end of the file `in01`, and running `./out00`. You should get the error message: -<pre><code> +``` xx not recognized. -</code></pre> +``` Pretty cool, huh? Anyways let's see how this compiler actually works. @@ -63,7 +63,7 @@ Writing in our stage 00 language is much nicer than editing an executable, because it's easier to move things around, and also, we can separate our program into lines! Let's take a look at the start: -<pre><code> +``` 7f 45 4c 46 02 01 @@ -90,7 +90,7 @@ a8 00 40 00 00 00 00 00 00 10 02 00 00 00 00 00 00 10 02 00 00 00 00 00 00 10 00 00 00 00 00 00 -</code></pre> +``` This is the ELF header and program header. It's just like our last one, but with a couple of differences. First, our entry point is at offset 0xa8 instead of 0x78. @@ -113,7 +113,7 @@ recognized."` - `00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00` (unused) Here's the data for our program. As you can see from my annotations, we have the -input and output file, as well as the error message. The command part of the +input and output file names, as well as the error message. The command part of the error message is left blank for now (we'll fill it in when the code is actually run). @@ -182,8 +182,8 @@ program with exit code 0 (successful). - `48 01 d8` `add rax, rbx` This here looks at the two bytes we read in (we'll call them `b1` and `b2`) and -computes `b1 * 128 + b2` (more specifically `(b1 << 7) + b2`). This is the index -in our command table corresponding to the two characters from the input file. +computes `b1 * 128 + b2` (more specifically `(b1 << 7) + b2`). This is the corresponding index +in our command table. - `48 c1 e0 03` `shl rax, 3` - `48 89 c3` `mov rbx, rax` @@ -211,7 +211,7 @@ is `03 48 89 c3`. We set the length to 0 for unused entries. So this code checks if the entry for this command starts with a zero byte. If it does, that means the two characters we read in don't actually correspond to a real command. If that's the case, this next bit of code is executed (otherwise -it's skiped over): +it's skipped over): - `48 b8 02 00 00 00 00 00 00 00` `mov rax, 2 (stderr)` - `48 89 c7` `mov rdi, rax` @@ -228,7 +228,7 @@ it's skiped over): - `00 00 00 00 00 00 00 00 00 00 00 00 00 00` (unused) This prints our error message, now filled in with the specific unrecognized -instruction, to standard error, and exits with code 1, to indicate failure. +instruction, to standard error, then exits with code 1, to indicate failure. - `48 89 eb` `mov rbx, rax` - `31 c0` `mov rax, 0` @@ -273,7 +273,7 @@ all the way back to read the next command. Otherwise, we keep looping. This skips over any comments/whitespace we might have between a command and the following command. -And that's all the *code* for this compiler. Next comes some data. +And that's all the *code* for this compiler. Next comes the command table. First, there's a whole bunch of unused 0s. Then there's the line @@ -293,7 +293,7 @@ Which is the encoding of the `syscall` instruction. You can look through the rest of the table, if you want. But let's look at the very end: -<code><pre> +``` 78 7f 45 4c 46 02 @@ -321,7 +321,7 @@ very end: 00 00 08 00 00 00 00 00 00 00 08 00 00 00 00 00 00 10 00 00 00 00 00 00 -</code></pre> +``` This is at the position for `||`, and it contains an ELF header. One thing you might notice is that we decided that each entry is 8 bytes long, but this one is @@ -340,5 +340,5 @@ fixed this, but frankly I've had enough of writing code in hexadecimal. So let's move on to [stage 02](../02/README.md), now that we have a nicer language on our hands. From now on, since we have comments, I'm gonna do most of the explaining in the source file -itself, rather than the README. But there'll still be a bit of stuff there each +itself, rather than the README. But there'll still be some stuff there each time. diff --git a/01/commands.txt b/01/commands.txt index 812b026..9cfdb1e 100644 --- a/01/commands.txt +++ b/01/commands.txt @@ -7,11 +7,12 @@ ff - Byte ff 'a - Character a (byte 0x61) '! - Character ! (byte 0x21) etc. +\n - Newline (byte 0x0a) zA - Zero rax im - Set rax to an immediate value, e.g. - im;05;00;00;00;00;00;00;00; - will set rax to 5. + im;05;00;00;00;00;00;00;00; + will set rax to 5. ax bx cx dx sp bp si di A B C D S R I J |