Patching functions smaller than JMP_SIZE overwrites whatever happens to follow them. On x86_64, this affects the the_ultimate_question function in mod tests; patching it causes the next function defined, default, to crash.

Previously 5 was always subtracted from the function address difference. This is wrong for short jumps (we only need to subtract 2) and causes all kinds of shenanigans (mostly segfaults, see the added test).

"Can not patch anything from std."

#![feature(print_internals)]

fn main() {
    std::mem::forget(guerrilla::patch1(std::io::_print, |_fmt_args|{
        panic!()
    }));
    println!("");
    return;
}

thread 'main' panicked at 'explicit panic', src/main.rs:X:Y

So I've tried to use the lib on my machine, using minimal example from your test suite, namely

src/main.rs

fn main() {
    println!("Hello, world!");
}

#[cfg(test)]
#[inline(never)]
fn the_ultimate_question() -> u32 {
    42
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_patch() {
        assert_eq!(the_ultimate_question(), 42);

        {
            let _guard = guerrilla::patch0(the_ultimate_question, || 24);

            assert_eq!(the_ultimate_question(), 24);
        }

        assert_eq!(the_ultimate_question(), 42);
    }
}

test result

I figured I'll show full trace as this is some low-level stuff

~/DEV/gtest master*
❯ RUST_BACKTRACE=full cargo test
    Finished test [unoptimized + debuginfo] target(s) in 0.01s
     Running unittests src/main.rs (target/debug/deps/gtest-3465a4636c308b16)

running 1 test
test tests::test_patch ... FAILED

failures:

---- tests::test_patch stdout ----
thread 'tests::test_patch' panicked at 'assertion failed: `(left == right)`
  left: `-1`,
 right: `0`', /Users/retard/.cargo/registry/src/github.com-1ecc6299db9ec823/guerrilla-0.1.4/src/lib.rs:48:5
stack backtrace:
   0:        0x105f75dd4 - std::backtrace_rs::backtrace::libunwind::trace::h0934ce8016da62ea
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:        0x105f75dd4 - std::backtrace_rs::backtrace::trace_unsynchronized::h59c3dee870344ec2
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:        0x105f75dd4 - std::sys_common::backtrace::_print_fmt::h498b4033e357b134
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys_common/backtrace.rs:66:5
   3:        0x105f75dd4 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h7d80e14dd19335c9
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys_common/backtrace.rs:45:22
   4:        0x105f919ab - core::fmt::write::h1709d0255080e28a
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/fmt/mod.rs:1198:17
   5:        0x105f72878 - std::io::Write::write_fmt::hc017b04bb9c972fa
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/io/mod.rs:1672:15
   6:        0x105f775ad - std::sys_common::backtrace::_print::h6f0d53db9de204c5
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys_common/backtrace.rs:48:5
   7:        0x105f775ad - std::sys_common::backtrace::print::h33928b4e9b284b1e
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys_common/backtrace.rs:35:9
   8:        0x105f775ad - std::panicking::default_hook::{{closure}}::had4d1cd22a173020
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:295:22
   9:        0x105f7728d - std::panicking::default_hook::h42aa124509888735
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:311:9
  10:        0x105f77ae8 - std::panicking::rust_panic_with_hook::h2b231e816574a23a
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:698:17
  11:        0x105f77a23 - std::panicking::begin_panic_handler::{{closure}}::h9da8d88b7a4c9d5e
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:588:13
  12:        0x105f76257 - std::sys_common::backtrace::__rust_end_short_backtrace::h10dbf1377dfaf877
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys_common/backtrace.rs:138:18
  13:        0x105f776fa - rust_begin_unwind
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:584:5
  14:        0x105f9c2f3 - core::panicking::panic_fmt::hde1544b10dc8b4d3
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/panicking.rs:142:14
  15:        0x105f90427 - core::panicking::assert_failed_inner::h153877a946e95f35
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/panicking.rs:224:17
  16:        0x105f980b4 - core::panicking::assert_failed::h0c952f10eaf20388
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/panicking.rs:181:5
  17:        0x105f153f8 - guerrilla::copy_to_protected_address::he7516577c438eb1d
                               at /Users/retard/.cargo/registry/src/github.com-1ecc6299db9ec823/guerrilla-0.1.4/src/lib.rs:48:5
  18:        0x105f13d8a - guerrilla::patch0::ha6c84ce43be61c5c
                               at /Users/retard/.cargo/registry/src/github.com-1ecc6299db9ec823/guerrilla-0.1.4/src/lib.rs:234:17
  19:        0x105f14acc - gtest::tests::test_patch::h510fbd743d2c030b
                               at /Users/retard/DEV/gtest/src/main.rs:20:26
  20:        0x105f14931 - gtest::tests::test_patch::{{closure}}::h2b0a69cc6c8c809c
                               at /Users/retard/DEV/gtest/src/main.rs:16:5
  21:        0x105f14dc1 - core::ops::function::FnOnce::call_once::h39bb4500dd86e6a3
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
  22:        0x105f4b166 - core::ops::function::FnOnce::call_once::hd3a34913c2b3782a
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
  23:        0x105f4b166 - test::__rust_begin_short_backtrace::h4585f9c5640ec448
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/test/src/lib.rs:572:5
  24:        0x105f4a145 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h845f99ab50caecd6
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/alloc/src/boxed.rs:1935:9
  25:        0x105f4a145 - <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::h65a0795f52888231
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/panic/unwind_safe.rs:271:9
  26:        0x105f4a145 - std::panicking::try::do_call::h7231d107ab6a7741
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:492:40
  27:        0x105f4a145 - std::panicking::try::hfb07ae8d672d4139
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:456:19
  28:        0x105f4a145 - std::panic::catch_unwind::hc098328b3bc35ceb
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panic.rs:137:14
  29:        0x105f4a145 - test::run_test_in_process::hc47b236ea8085ef3
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/test/src/lib.rs:595:18
  30:        0x105f4a145 - test::run_test::run_test_inner::{{closure}}::h6f1cb5c72f6693fa
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/test/src/lib.rs:489:39
  31:        0x105f157eb - test::run_test::run_test_inner::{{closure}}::hf20ba670a38e248e
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/test/src/lib.rs:516:37
  32:        0x105f157eb - std::sys_common::backtrace::__rust_begin_short_backtrace::h59cf3b5757eeaaa1
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys_common/backtrace.rs:122:18
  33:        0x105f1b9ac - std::thread::Builder::spawn_unchecked_::{{closure}}::{{closure}}::h5edd03a29d1385f8
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/thread/mod.rs:505:17
  34:        0x105f1b9ac - <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::h2985eae67b18a09c
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/panic/unwind_safe.rs:271:9
  35:        0x105f1b9ac - std::panicking::try::do_call::ha5aa2ce6f0450132
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:492:40
  36:        0x105f1b9ac - std::panicking::try::hd07d6a5dc8988e62
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:456:19
  37:        0x105f1b9ac - std::panic::catch_unwind::h9c8fcaf2d1139ea8
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panic.rs:137:14
  38:        0x105f1b9ac - std::thread::Builder::spawn_unchecked_::{{closure}}::h4476f28265ee914a
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/thread/mod.rs:504:30
  39:        0x105f1b9ac - core::ops::function::FnOnce::call_once{{vtable.shim}}::hce479c2981b1129e
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
  40:        0x105f7bf87 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb8ffae40895b6568
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/alloc/src/boxed.rs:1935:9
  41:        0x105f7bf87 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h2e872f74d95473f3
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/alloc/src/boxed.rs:1935:9
  42:        0x105f7bf87 - std::sys::unix::thread::Thread::new::thread_start::h76e6c1c658a39a87
                               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/sys/unix/thread.rs:108:17
  43:     0x7fff6df90109 - __pthread_start


failures:
    tests::test_patch

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s

error: test failed, to rerun pass '--bin gtest'

my platform

~/DEV/gtest master*
❯ rustc -vV
rustc 1.64.0 (a55dd71d5 2022-09-19)
binary: rustc
commit-hash: a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52
commit-date: 2022-09-19
host: x86_64-apple-darwin
release: 1.64.0
LLVM version: 14.0.6

~/DEV/gtest master*
❯ cargo -vV
cargo 1.64.0 (387270bc7 2022-09-16)
release: 1.64.0
commit-hash: 387270bc7f446d17869c7f208207c73231d6a252
commit-date: 2022-09-16
host: x86_64-apple-darwin
libgit2: 1.4.2 (sys:0.14.2 vendored)
libcurl: 7.64.1 (sys:0.4.55+curl-7.83.1 system ssl:(SecureTransport) LibreSSL/2.8.3)
os: Mac OS 10.15.7 [64-bit]

help pl0x

Currently there's the patch* functions which accept from 0 to 9 arguments, which is a limitation when it comes to a larger amount, which is surely non-idiomatic and not practical but can sometimes happen in FFI scenarios. Aside of that, the numbering just looks ugly. A patch! macro (likely implemented as a tiny separate crate decoupled from the patch guard and then reexported in the main crate because that's how proc-macro crates work) is a much cleaner way, I think.

Hello, first of all, I am really amazed by this crate! But I am not able to understand, what is really going on under the hood to achieve this functionality. Therefore my first idea was to use your crate for mocking purposes in tests. Sadly, your implementation is not thread safe, reproducible example below:

#[cfg(test)]
extern crate guerrilla;

fn function_int() -> i32 { 1 }

fn function_str() -> &'static str { "original" }

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_int_default() {
        assert_eq!(function_int(), 1);
    }

    #[test]
    fn test_int_mock_1() {
        guerrilla::patch0(function_int, || 5);
        assert_eq!(function_int(), 5);
    }

    #[test]
    fn test_int_mock_2() {
        guerrilla::patch0(function_int, || 2);
        assert_eq!(function_int(), 2);
    }

    #[test]
    fn test_str_default() {
        assert_eq!(function_str(), "original");
    }

    #[test]
    fn test_str_mock_1() {
        guerrilla::patch0(function_str, || "mock_1");
        assert_eq!(function_str(), "mock_1");
    }

    #[test]
    fn test_str_mock_2() {
        guerrilla::patch0(function_str, || "mock_2");
        assert_eq!(function_str(), "mock_2");
    }
}

(Execute this a couple times to see random failures and random successful runs. Runs perfectly fine with cargo test -- --test-threads 1.)

Is it possible, to achieve thread safety? And would it be something you would like to implement? I would really appreciate it :)

Thank you!

This is very much a duplicate of #3, but it seems like you had problems consistently reproducing the problem in tests. I put together a proof of concept which (at least on my machines) consistently shows the described problem here.

Unfortunately, I'm not sure how to turn this into a unit test as it relies on turning on size optimization (opt-level = "s") and requires the functions to be defined in another crate in order to avoid inlining. If you can think of a way to turn this into a test or just want to use the code for debugging purposes, feel free to do so!

This is inherent to the API, as there's no reasonable interpretation of what version to "restore" in such a case; so it might just be one for the "no monkey business" section of the manual