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Support heaps with no offset-guard pages.

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Also, say "guard-offset pages" rather than just "guard pages" to describe the
region of a heap which is never accessible and which exists to support
optimizations for heap accesses with offsets.

And, introduce a `Uimm64` immediate type, and make all heap fields use
`Uimm64` instead of `Imm64` since they really are unsigned.
This commit is contained in:
Dan Gohman
2018-11-29 04:53:30 -08:00
parent 93696a80bb
commit a20c852148
27 changed files with 302 additions and 172 deletions
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24
lib/wasm/src/code_translator.rs
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@@ -992,20 +992,20 @@ fn get_heap_addr(
) -> (ir::Value, i32) {
use std::cmp::min;
let guard_size: i64 = builder.func.heaps[heap].guard_size.into();
debug_assert!(guard_size > 0, "Heap guard pages currently required");
let mut adjusted_offset = u64::from(offset);
let offset_guard_size: u64 = builder.func.heaps[heap].offset_guard_size.into();
// Generate `heap_addr` instructions that are friendly to CSE by checking offsets that are
// multiples of the guard size. Add one to make sure that we check the pointer itself is in
// bounds.
//
// For accesses on the outer skirts of the guard pages, we expect that we get a trap
// even if the access goes beyond the guard pages. This is because the first byte pointed to is
// inside the guard pages.
let check_size = min(
i64::from(u32::MAX),
1 + (i64::from(offset) / guard_size) * guard_size,
) as u32;
// multiples of the offset-guard size. Add one to make sure that we check the pointer itself
// is in bounds.
if offset_guard_size != 0 {
adjusted_offset = adjusted_offset / offset_guard_size * offset_guard_size;
}
// For accesses on the outer skirts of the offset-guard pages, we expect that we get a trap
// even if the access goes beyond the offset-guard pages. This is because the first byte
// pointed to is inside the offset-guard pages.
let check_size = min(u64::from(u32::MAX), 1 + adjusted_offset) as u32;
let base = builder.ins().heap_addr(addr_ty, heap, addr32, check_size);
// Native load/store instructions take a signed `Offset32` immediate, so adjust the base