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6529 - don't let `addr`s escape functions 

I've gone back and forth on this. I initially disallowed this, then allowed
it because I forgot why I disallowed it. The reason to disallow it: if
you return an `addr` to a variable allocated on the stack, the space might
be reused for a different type, which violates type-safety. And once you
can reinterpret bits of one type as another you lose memory-safety as well.

This has some interesting implications for Mu programs; certain kinds of
helper functions become impossible to write. Now I find myself relying a
lot more on scopes (and editor folding support) for abstracting details.
And they won't help manage duplication. We'll see how this goes.

While I'm being draconian about `addr`s on the stack, I'm still abusing
`addr`s on the heap, with the expectation that future checks on reclamation
will protect me. The boon and bane of stack space is that it's constantly
reclaimed.
This commit is contained in:
Kartik Agaram 2020-06-15 17:00:26 -07:00
parent 5a6d2d0db7
commit d292196ff5
2 changed files with 24 additions and 19 deletions
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40
apps/browse.mu
View File

@ -6,9 +6,27 @@
#
# Press 'q' to quit. All other keys scroll down.
fn main args: (addr array (addr array byte)) -> exit-status/ebx: int {
var filename/eax: (addr array byte) <- first-arg args
var file/esi: (addr buffered-file) <- load-file filename
fn main args-on-stack: (addr array (addr array byte)) -> exit-status/ebx: int {
# var file/esi: (addr buffered-file) = open args-on-stack[1] for reading {{{
var file/esi: (addr buffered-file) <- copy 0
{
var file-handle: (handle buffered-file)
{
var address-of-file-handle/esi: (addr handle buffered-file) <- address file-handle
# var filename/ecx: (addr array byte) = args-on-stack[1] {{{
var filename/ecx: (addr array byte) <- copy 0
{
var args/eax: (addr array (addr array byte)) <- copy args-on-stack
var tmp/eax: (addr addr array byte) <- index args, 1
filename <- copy *tmp
}
# }}}
open filename, 0, address-of-file-handle
}
var tmp/eax: (addr buffered-file) <- lookup file-handle
file <- copy tmp
}
# }}}
enable-screen-grid-mode
var nrows/eax: int <- copy 0
var ncols/ecx: int <- copy 0
@ -154,22 +172,6 @@ fn clear toprow: int, leftcol: int, botrow: int, rightcol: int {
}
}
fn first-arg args-on-stack: (addr array (addr array byte)) -> out/eax: (addr array byte) {
var args/eax: (addr array (addr array byte)) <- copy args-on-stack
var result/eax: (addr addr array byte) <- index args, 1
out <- copy *result
}
fn load-file filename: (addr array byte) -> out/esi: (addr buffered-file) {
var result: (handle buffered-file)
{
var tmp1/eax: (addr handle buffered-file) <- address result
open filename, 0, tmp1
}
var tmp2/eax: (addr buffered-file) <- lookup result
out <- copy tmp2
}
fn dump in: (addr buffered-file) {
var c/eax: byte <- read-byte-buffered in
compare c, 0xffffffff # EOF marker

3
apps/mu.subx
View File

@ -4638,6 +4638,9 @@ $parse-mu:error2:
# ✓ fn foo x: int {
# ✓ fn foo x: int {
# ✓ fn foo x: int -> y/eax: int {
# TODO:
# disallow outputs of type `(... addr ...)`
# disallow inputs of type `(... addr ... addr ...)`
populate-mu-function-header: # first-line: (addr stream byte), out: (addr function), vars: (addr stack live-var), err: (addr buffered-file), ed: (addr exit-descriptor)
# pseudocode:
# var name: slice