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| author | Kartik K. Agaram <vc@akkartik.com> | 2021-03-03 22:09:50 -0800 |
|---|---|---|
| committer | Kartik K. Agaram <vc@akkartik.com> | 2021-03-03 22:21:03 -0800 |
| commit | 71e4f3812982dba2efb471283d310224e8db363e (patch) | |
| tree | ea111a1acb8b8845dbda39c0e1b4bac1d198143b /linux/ex8.subx | |
| parent | c6b928be29ac8cdb4e4d6e1eaa20420ff03e5a4c (diff) | |
| download | mu-71e4f3812982dba2efb471283d310224e8db363e.tar.gz | |
7842 - new directory organization
Baremetal is now the default build target and therefore has its sources
at the top-level. Baremetal programs build using the phase-2 Mu toolchain
that requires a Linux kernel. This phase-2 codebase which used to be at
the top-level is now under the linux/ directory. Finally, the phase-2 toolchain,
while self-hosting, has a way to bootstrap from a C implementation, which
is now stored in linux/bootstrap. The bootstrap C implementation uses some
literate programming tools that are now in linux/bootstrap/tools.
So the whole thing has gotten inverted. Each directory should build one
artifact and include the main sources (along with standard library). Tools
used for building it are relegated to sub-directories, even though those
tools are often useful in their own right, and have had lots of interesting
programs written using them.
A couple of things have gotten dropped in this process:
- I had old ways to run on just a Linux kernel, or with a Soso kernel.
No more.
- I had some old tooling for running a single test at the cursor. I haven't
used that lately. Maybe I'll bring it back one day.
The reorg isn't done yet. Still to do:
- redo documentation everywhere. All the README files, all other markdown,
particularly vocabulary.md.
- clean up how-to-run comments at the start of programs everywhere
- rethink what to do with the html/ directory. Do we even want to keep
supporting it?
In spite of these shortcomings, all the scripts at the top-level, linux/
and linux/bootstrap are working. The names of the scripts also feel reasonable.
This is a good milestone to take stock at.
Diffstat (limited to 'linux/ex8.subx')
| -rw-r--r-- | linux/ex8.subx | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/linux/ex8.subx b/linux/ex8.subx new file mode 100644 index 00000000..84d27195 --- /dev/null +++ b/linux/ex8.subx @@ -0,0 +1,60 @@ +# Example reading commandline arguments: compute length of first arg. +# +# To run: +# $ ./bootstrap translate init.linux apps/ex8.subx -o apps/ex8 +# $ ./bootstrap run apps/ex8 abc de fghi +# Expected result: +# $ echo $? +# 3 # length of 'abc' +# +# At the start of a SubX program: +# argc: *esp +# argv[0]: *(esp+4) +# argv[1]: *(esp+8) +# ... +# Locals start from esp-4 downwards. + +== code +# instruction effective address register displacement immediate +# . op subop mod rm32 base index scale r32 +# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes + +Entry: + # . prologue + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # eax = ascii-length(argv[1]) + # . . push args + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) + # . . call + e8/call ascii-length/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + + # exit(eax) + 89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx + e8/call syscall_exit/disp32 + +ascii-length: # s: (addr array byte) -> n/eax + # edx = s + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 4/disp8 . # copy *(esp+4) to edx + # var result/eax = 0 + b8/copy-to-eax 0/imm32 +$ascii-length:loop: + # var c/ecx = *s + 8a/copy-byte 0/mod/* 2/rm32/edx . . . 1/r32/CL . . # copy byte at *edx to CL + # if (c == '\0') break + 81 7/subop/compare 3/mod/direct 1/rm32/ecx . . . . . 0/imm32/null # compare ecx + 74/jump-if-= $ascii-length:end/disp8 + # ++s + 42/increment-edx + # ++result + 40/increment-eax + # loop + eb/jump $ascii-length:loop/disp8 +$ascii-length:end: + # return eax + c3/return + +== data + +# . . vim:nowrap:textwidth=0 |