From 87bb0bee6b9843ea32ca6bb48f9e03b1876b7c48 Mon Sep 17 00:00:00 2001 From: Alan Wu Date: Fri, 21 Oct 2022 17:06:34 -0400 Subject: [PATCH] YJIT: Fix page rounding for icache busting Previously, we found the current page by rounding the current pointer to the closest smaller page size. This is incorrect because pages are relative to the start of the address we reserve. For example, if the starting address is 12KiB modulo the 16KiB page size, once we have more than 4KiB of code, calculating with the address would incorrectly give us page 1 when we're actually still on page 0. Previously, I can reproduce crashes with: make btest RUN_OPTS=--yjit-code-page-size=32 on ARM64 macOS, where system page sizes are 16KiB. --- yjit/src/asm/mod.rs | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/yjit/src/asm/mod.rs b/yjit/src/asm/mod.rs index 61c1523aab..ab7c4d6aba 100644 --- a/yjit/src/asm/mod.rs +++ b/yjit/src/asm/mod.rs @@ -217,12 +217,14 @@ impl CodeBlock { #[cfg(any(feature = "disasm", target_arch = "aarch64"))] pub fn writable_addrs(&self, start_ptr: CodePtr, end_ptr: CodePtr) -> Vec<(usize, usize)> { let mut addrs = vec![]; - let mut start = start_ptr.raw_ptr() as usize; - let codeblock_end = self.get_ptr(self.get_mem_size()).raw_ptr() as usize; - let end = std::cmp::min(end_ptr.raw_ptr() as usize, codeblock_end); + let mut start = start_ptr.into_usize(); + let region_start = self.get_ptr(0).into_usize(); + let region_end = self.get_ptr(self.get_mem_size()).into_usize(); + let end = std::cmp::min(end_ptr.into_usize(), region_end); while start < end { - let current_page = start / self.page_size * self.page_size; - let page_end = std::cmp::min(end, current_page + self.page_end()) as usize; + let current_page = region_start + + (start.saturating_sub(region_start) / self.page_size * self.page_size); + let page_end = std::cmp::min(end, current_page + self.page_end()); addrs.push((start, page_end)); start = current_page + self.page_size + self.page_start(); }