Re:Neat Rust Tricks: Passing Closures to C
by rabidferret on Monday November 25, 2019 @06:23PM
(#21633988)
Anything that doesn't require W+X would need an entire page allocated per closure, wouldn't it?
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Re:Neat Rust Tricks: Passing Closures to C
by devit on Monday November 25, 2019 @07:58PM
(#21634706)
No, you can of course allocate W+X pages from the OS and put multiple closures in them using a standard userspace memory allocator.
Or if the OS doesn't support W+X allocation at all, then you can have a bunch of tightly packed pregenerated trampolines in the binary.
Re:Neat Rust Tricks: Passing Closures to C
by saagarjha on Monday November 25, 2019 @08:26PM
(#21634861)
Right, this is how Objective-C's implementation works, except it keeps around one page of trampolines and remaps that around when necessary to be able to "create" more trampolines on the fly, I believe.
Re:Neat Rust Tricks: Passing Closures to C
by a1369209993 on Monday November 25, 2019 @10:58PM
(#21635551)
Nope! You'd do something to the effect of:
clo_code:
4C8B1501100000 mov r10 [rel clo_code+0x1008]
FF25F30F0000 jmp [rel clo_code+0x1000]
0F1F00 nop3
# one page away...
struct clo_slot {
void (*func)(void* _R10,...);
void* data;
};