From d6b06b8a327ff32d083bc0494cc3195d9f8082d2 Mon Sep 17 00:00:00 2001 From: Alex Crichton Date: Fri, 5 Mar 2021 08:43:25 -0800 Subject: [PATCH] std: Fix a bug on the wasm32-wasi target opening files This commit fixes an issue pointed out in #82758 where LTO changed the behavior of a program. It turns out that LTO was not at fault here, it simply uncovered an existing bug. The bindings to `__wasilibc_find_relpath` assumed that the relative portion of the path returned was always contained within thee input `buf` we passed in. This isn't actually the case, however, and sometimes the relative portion of the path may reference a sub-portion of the input string itself. The fix here is to use the relative path pointer coming out of `__wasilibc_find_relpath` as the source of truth. The `buf` used for local storage is discarded in this function and the relative path is copied out unconditionally. We might be able to get away with some `Cow`-like business or such to avoid the extra allocation, but for now this is probably the easiest patch to fix the original issue. --- library/std/src/sys/wasi/fs.rs | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/library/std/src/sys/wasi/fs.rs b/library/std/src/sys/wasi/fs.rs index bcf7da46b4b07..63c22136273fb 100644 --- a/library/std/src/sys/wasi/fs.rs +++ b/library/std/src/sys/wasi/fs.rs @@ -650,13 +650,11 @@ fn open_parent(p: &Path) -> io::Result<(ManuallyDrop, PathBuf)> { ); return Err(io::Error::new(io::ErrorKind::Other, msg)); } - let len = CStr::from_ptr(buf.as_ptr().cast()).to_bytes().len(); - buf.set_len(len); - buf.shrink_to_fit(); + let relative = CStr::from_ptr(relative_path).to_bytes().to_vec(); return Ok(( ManuallyDrop::new(WasiFd::from_raw(fd as u32)), - PathBuf::from(OsString::from_vec(buf)), + PathBuf::from(OsString::from_vec(relative)), )); } }