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Merge pull request #4389 from RalfJung/native-lib-search-order

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native_lib: skip to next .so if function was in dependency of the first
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Ralf Jung 2025-06-10 09:11:49 +00:00 • committed by GitHub
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2 changed files with 25 additions and 22 deletions
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22
src/tools/miri/README.md
View file

@ -396,20 +396,22 @@ to Miri failing to detect cases of undefined behavior in a program.
* `-Zmiri-force-intrinsic-fallback` forces the use of the "fallback" body for all intrinsics that
have one. This is useful to test the fallback bodies, but should not be used otherwise. It is
**unsound** since the fallback body might not be checking for all UB.
* `-Zmiri-native-lib=<path to a shared object file>` is an experimental flag for providing support
for calling native functions from inside the interpreter via FFI. The flag is supported only on
Unix systems. Functions not provided by that file are still executed via the usual Miri shims. If
a path to a directory is specified, all files in that directory are included nonrecursively. This
flag can be passed multiple times to specify multiple files and/or directories.
* `-Zmiri-native-lib=<path to a shared object file or folder>` is an experimental flag for providing
support for calling native functions from inside the interpreter via FFI. The flag is supported
only on Unix systems. Functions not provided by that file are still executed via the usual Miri
shims. If a path to a directory is specified, all files in that directory are included
non-recursively. This flag can be passed multiple times to specify multiple files and/or
directories.
**WARNING**: If an invalid/incorrect `.so` file is specified, this can cause Undefined Behavior in
Miri itself! And of course, Miri often cannot do any checks on the actions taken by the native code.
Note that Miri has its own handling of file descriptors, so if you want to replace *some*
functions working on file descriptors, you will have to replace *all* of them, or the two kinds of
file descriptors will be mixed up. This is **work in progress**; currently, only integer and
pointers arguments and return values are supported and memory allocated by the native code cannot
be accessed from Rust (only the other way around). Native code must not spawn threads that keep
running in the background after the call has returned to Rust and that access Rust-allocated
memory. Finally, the flag is **unsound** in the sense that Miri stops tracking details such as
file descriptors will be mixed up.
This is **work in progress**; currently, only integer and pointers arguments and return values are
supported and memory allocated by the native code cannot be accessed from Rust (only the other way
around). Native code must not spawn threads that keep running in the background after the call has
returned to Rust and that access Rust-allocated memory.
Finally, the flag is **unsound** in the sense that Miri stops tracking details such as
initialization and provenance on memory shared with native code, so it is easily possible to write
code that has UB which is missed by Miri.
* `-Zmiri-measureme=<name>` enables `measureme` profiling for the interpreted program.

25
src/tools/miri/src/shims/native_lib.rs
View file

@ -114,18 +114,19 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
// using the `libc` crate where this interface is public.
let mut info = std::mem::MaybeUninit::<libc::Dl_info>::zeroed();
unsafe {
if libc::dladdr(fn_ptr, info.as_mut_ptr()) != 0 {
let info = info.assume_init();
#[cfg(target_os = "cygwin")]
let fname_ptr = info.dli_fname.as_ptr();
#[cfg(not(target_os = "cygwin"))]
let fname_ptr = info.dli_fname;
assert!(!fname_ptr.is_null());
if std::ffi::CStr::from_ptr(fname_ptr).to_str().unwrap()
!= lib_path.to_str().unwrap()
{
return None;
}
let res = libc::dladdr(fn_ptr, info.as_mut_ptr());
assert!(res != 0, "failed to load info about function we already loaded");
let info = info.assume_init();
#[cfg(target_os = "cygwin")]
let fname_ptr = info.dli_fname.as_ptr();
#[cfg(not(target_os = "cygwin"))]
let fname_ptr = info.dli_fname;
assert!(!fname_ptr.is_null());
if std::ffi::CStr::from_ptr(fname_ptr).to_str().unwrap()
!= lib_path.to_str().unwrap()
{
// The function is not actually in this .so, check the next one.
continue;
}
}