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Diffstat (limited to 'subx/Readme.md')
| -rw-r--r-- | subx/Readme.md | 61 |
1 files changed, 32 insertions, 29 deletions
diff --git a/subx/Readme.md b/subx/Readme.md index 3e7f0e68..39139641 100644 --- a/subx/Readme.md +++ b/subx/Readme.md @@ -526,32 +526,9 @@ stack, at the OS syscall level. The idea is that every syscall that interacts with hardware (and so the environment) should be *dependency injected* so that it's possible to insert fake hardware in tests. -The hypothesis is that designing the entire system to be testable from day 1 -and from the ground up would radically impact the culture of the eco-system in -a way that no bolted-on tool or service at higher levels can replicate: - -* Tests would make it easier to write programs that can be easily understood - by newcomers. - -* More broad-based understanding would lead to more forks. - -* Tests would make it easy to share code across forks. Copy the tests over, - and then copy code over and polish it until the tests pass. Manual work, but - tractable and without major risks. - -* The community would gain a diversified portfolio of forks for each program, - a “wavefront” of possible combinations of features and alternative - implementations of features. Application writers who wrote thorough tests - for their apps (something they just can’t do today) would be able to bounce - around between forks more easily without getting locked in to a single one - as currently happens. - -* There would be a stronger culture of reviewing the code for programs you use - or libraries you depend on. [More eyeballs would make more bugs shallow.](https://en.wikipedia.org/wiki/Linus%27s_Law) - But those are big goals. Here are the syscalls I have so far: -1. `write`: takes two arguments, a file `f` and an address to array `s`. +* `write`: takes two arguments, a file `f` and an address to array `s`. Comparing this interface with the Unix `write()` syscall shows two benefits: @@ -562,7 +539,7 @@ But those are big goals. Here are the syscalls I have so far: SubX's wrapper keeps the two together to increase the chances that we never accidentally go out of array bounds. -1. `read`: takes two arguments, a file `f` and an address to stream `s`. Reads +* `read`: takes two arguments, a file `f` and an address to stream `s`. Reads as much data from `f` as can fit in (the free space of) `s`. Like with `write()`, this wrapper around the Unix `read()` syscall adds the @@ -573,7 +550,7 @@ But those are big goals. Here are the syscalls I have so far: to another. See [the comments before the implementation](http://akkartik.github.io/mu/html/subx/058read.subx.html) for a discussion of alternative interfaces. -1. `stop`: takes two arguments: +* `stop`: takes two arguments: - `ed` is an address to an _exit descriptor_. Exit descriptors allow us to `exit()` the program in production, but return to the test harness within tests. That allows tests to make assertions about when `exit()` is called. @@ -582,13 +559,13 @@ But those are big goals. Here are the syscalls I have so far: For more details on exit descriptors and how to create one, see [the comments before the implementation](http://akkartik.github.io/mu/html/subx/057stop.subx.html). -1. `new-segment` +* `new-segment` Allocates a whole new segment of memory for the program, discontiguous with both existing code and data (heap) segments. Just a more opinionated form of [`mmap`](http://man7.org/linux/man-pages/man2/mmap.2.html). -1. `allocate`: takes two arguments, an address to allocation-descriptor `ad` +* `allocate`: takes two arguments, an address to allocation-descriptor `ad` and an integer `n` Allocates a contiguous range of memory that is guaranteed to be exclusively @@ -601,7 +578,7 @@ But those are big goals. Here are the syscalls I have so far: management, where a sub-system gets a chunk of memory and further parcels it out to individual allocations. Particularly helpful for (surprise) tests. -1. ... _(to be continued)_ +* ... _(to be continued)_ I will continue to import syscalls over time from [the old Mu VM in the parent directory](https://github.com/akkartik/mu), which has experimented with @@ -693,6 +670,32 @@ from a slice: * `skip-chars-matching-in-slice`: curr, end, delimiter byte -> new-curr (in `EAX`) * `skip-chars-not-matching-in-slice`: curr, end, delimiter byte -> new-curr (in `EAX`) +## Conclusion + +The hypothesis of Mu and SubX is that designing the entire system to be +testable from day 1 and from the ground up would radically impact the culture +of the eco-system in a way that no bolted-on tool or service at higher levels +can replicate: + +* Tests would make it easier to write programs that can be easily understood + by newcomers. + +* More broad-based understanding would lead to more forks. + +* Tests would make it easy to share code across forks. Copy the tests over, + and then copy code over and polish it until the tests pass. Manual work, but + tractable and without major risks. + +* The community would gain a diversified portfolio of forks for each program, + a “wavefront” of possible combinations of features and alternative + implementations of features. Application writers who wrote thorough tests + for their apps (something they just can’t do today) would be able to bounce + around between forks more easily without getting locked in to a single one + as currently happens. + +* There would be a stronger culture of reviewing the code for programs you use + or libraries you depend on. [More eyeballs would make more bugs shallow.](https://en.wikipedia.org/wiki/Linus%27s_Law) + ## Resources * [Single-page cheatsheet for the x86 ISA](https://net.cs.uni-bonn.de/fileadmin/user_upload/plohmann/x86_opcode_structure_and_instruction_overview.pdf) |