nostd

src/dwarf/divination.rs

@@ -0,0 +1,69 @@
+//! # divination
+//!
+//! the practice of seeking knowledge of the future or the unknown by supernatural means.
+//!
+//! we ask supernatural means (the dynamic linker) for knowledge of the future
+//! (where we will find the dwarves)
+//!
+//! first, we ask the dynamic linker to give us the `.eh_frame` for the current binary using
+//! the GNU extension (`_dl_find_object`)[https://www.gnu.org/software/libc/manual/html_node/Dynamic-Linker-Introspection.html].
+//! then, we parse that as beautiful DWARF call frame information, as god (or rather, the x86-64 psABI) intended.
+
+use core::ffi;
+
+use crate::stdext::with_last_os_error_str;
+
+#[allow(non_camel_case_types)]
+#[repr(C)]
+struct dl_find_object {
+    dlfo_flags: ffi::c_ulonglong,
+    dlfo_map_start: *const ffi::c_void,
+    dlfo_map_end: *const ffi::c_void,
+    dlf_link_map: *const ffi::c_void,
+    dlfo_eh_frame: *const ffi::c_void,
+}
+
+extern "C" {
+    fn _dl_find_object(address: *const ffi::c_void, result: *mut dl_find_object) -> ffi::c_int;
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct DwarfInfo {
+    /// The text segment
+    map: *const [u8],
+    /// PT_GNU_EH_FRAME
+    dwarf: *const u8,
+}
+
+pub fn dwarf_info(addr: *const ffi::c_void) -> Option<DwarfInfo> {
+    unsafe {
+        let mut out = core::mem::zeroed();
+        let ret = _dl_find_object(addr, &mut out);
+        trace!("dl_find_object returned {ret}");
+        if ret != 0 {
+            with_last_os_error_str(|err| trace!("dl_find_object error: {err}"));
+            return None;
+        }
+        if out.dlfo_eh_frame.is_null() {
+            return None;
+        }
+
+        let text_len = out.dlfo_map_end as usize - out.dlfo_map_start as usize;
+        trace!(
+            "dwarf info; map: ({:p}, {:x}), dwarf: {:p}",
+            out.dlfo_map_start,
+            text_len,
+            out.dlfo_eh_frame
+        );
+
+        if !(out.dlfo_map_start..out.dlfo_map_end).contains(&addr) {
+            trace!("dl_find_object returned object out of range for addr: {addr:p}");
+            return None;
+        }
+
+        Some(DwarfInfo {
+            map: core::ptr::slice_from_raw_parts(out.dlfo_map_start as _, text_len),
+            dwarf: out.dlfo_eh_frame as _,
+        })
+    }
+}