panic_detector#

pw_kernel: Kernel experiments

panic_detector will scan a rust binary and through static analysis display a list of all panic call sites.

Currently only riscv32 elf files are supported.

Usage#

panic_detector can be integrated into the bazel build as follows:

1. Add panic handler#

Add a panic handler to the rust binary which will be used by panic_detector to find the panic call sites.

#[panic_handler]
fn panic_handler(info: &core::panic::PanicInfo) -> ! {
    if let Some(location) = info.location() {
        panic_is_possible(location.file().as_ptr(), location.file().len(), location.line(), location.column());
    } else {
        panic_is_possible(core::ptr::null(), 0, 0, 0);
    }
}

#[no_mangle]
#[inline(never)]
extern "C" fn panic_is_possible(filename: *const u8, filename_len: usize, line: u32, col: u32) -> !{
    // The arguments to this function are reverse-engineereddocs.html
    // from the machine code by static analysis to
    // display a list of all the panic call-sites to the
    // user in the mutask_no_panic_test() error message.
    // See welder/src/check_panic.rs for more details.

    // If this symbol exists in the binary, panics are
    // possible. Presubmit tests can ensure that this symbol
    // does not exist in the final binary.  Do not rename or
    // remove this function.
    core::hint::black_box(filename);
    core::hint::black_box(filename_len);
    core::hint::black_box(line);
    core::hint::black_box(col);
    loop {}
}

2. Add a test target#

Add a test target to bazel for the binary to validate.

rust_binary(
    name = "example",
    srcs = ["main.rs"],
)

load("//pw_kernel/tooling/panic_detector:rust_binary_no_panics_test.bzl", "rust_binary_no_panics_test")

rust_binary_no_panics_test(
    name = "example_no_panic_test",
    binary = ":example",
)

3. Run the bazel test#

If any panics are detected panic_detector will print the locations to stdout.

$ bazel test //:example_no_panic_test
<snip>
Found panic ufmt-0.2.0/src/helpers.rs line 58 column 13. Branch trace:
  00103896 lui      a0,0x104           (task0_entry)
  0010389e jal      ra,-1734           (task0_entry)
  0010320a jalr     ra,ra,-82          (panic_const_add_overflow)
  001031d2 jalr     ra,ra,-78          (core::panicking::panic_fmt)
  00103192 jal      ra,2               (rust_begin_unwind)
  00103194 addi     sp,sp,-16          (panic_is_possible)
  <snip>
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