| Commit message (Collapse) | Author | Age | Files | Lines |
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Let's start highlighting all global variables in Red. Assembly programming
has a tendency to over-use them. They're a necessary evil, but we should
minimize the number of functions that access them.
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Standardize on hyphens in all names.
And we'll use colons for namespacing labels in functions.
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Make segment management a little more consistent between initial segments
and add-on segments (using `mmap`).
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Start requiring a '-o' flag to designate the output binary when translating.
Things currently get funky if you pass in multiple inputs, but that's ok.
This is the first step to supporting multiple input files for a single
output binary.
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When I started SubX I imagined that being able to write machine code directly
was a feature. Now it's just a hole I haven't bothered closing yet.
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It was broken since I added support for global variables, back on Sep 1.
One other subtle thing I've improved is the name `looks_like_hex_int`.
We can now distinguish in the pack-operands transform between ignoring
'foo' because it doesn't look like a number, and immediately flagging '0xfoo'
as an error because it *should* be a number.
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More calling convention tweaks.
Use EBP to get consistently at parameters and locals.
Always put the first function argument closest to EBP.
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New helper: compare a null-terminated string (from argv) with a length-prefixed
string (anywhere else).
As long as ex11 continues to pass we can copy the function and its tests
to other programs.
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Include LEA (load effective address) in the SubX subset of x86 ISA.
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One of the more painful things I had to debug with machine code. Tricks
I used can be seen in ex10.subx:
- printing argv[1] in various places
- printing a single 'X' in various places to count how many times we get
to different instructions
- exiting with the current value of EAX in various places
I repeatedly went down the wrong trail in several ways:
- forgetting that the problem lay in native runs, and accidentally switching
to subx runs during debugging.
- forgetting to pass commandline args, because ex10 doesn't check its argv
- writing the wrong comment for an instruction, and then miscalculating
the set of registers that need to be saved.
- forgetting that syscalls clobber EAX.
Debugging native runs is hard, because you have to write non-trivial code
to instrument the binary, and instrumentation can itself be buggy.
When we finally tracked it down, I recognized the problem immediately.
I'd meant to confirm the behavior of opcode 8a against bare metal, and
then forgot.
In any case, opcode 8a was inconsistent with 88. Sloppy.
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subx/examples/ex10 doesn't currently run natively. Grr..
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Even more cuddling. We want to keep lines short where the opcode and operands
are self-explanatory.
If there are any implicit registers, etc., we'll continue to do the table
layout.
The first two columns look messy now; let's see how this goes.
Maybe I'll give up on the tabular layout altogether, just string args with
a single space.
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Since we're cuddling jump/call args next to the opcode, we can have longer
labels without messing up the layout!
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New example program: ascii null-terminated string comparison
I'd hoped this would be a stepping stone to supporting general ascii comparison,
but we're planning to use size-prefixed rather than null-terminated arrays
everywhere. The only exception is commandline arguments, which will remain
null-terminated to interoperate with Linux.
So I'm going to need separate functions for "compare with argv" and for
general string comparison.
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New example, just to fix in my head how arguments go on the stack.
It's possible I'm still confused about the order callers push args in to
the stack. But even if this violates the calling convention, it should
still run.
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