Add method to get PHDR from aux vector

Cargo.toml

@@ -19,6 +19,8 @@ gimli = { git = "https://github.com/gimli-rs/gimli.git" }
 alloc = []
 unwinder = []
 fde-phdr = ["libc"]
+fde-phdr-dl = ["fde-phdr"]
+fde-phdr-aux = ["fde-phdr"]
 fde-registry = ["alloc"]
 fde-static = []
 fde-gnu-eh-frame-hdr = []
@@ -31,7 +33,7 @@ panic = ["alloc"]
 panic-handler = ["print", "panic"]
 panic-handler-dummy = []
 system-alloc = []
-default = ["unwinder", "dwarf-expr", "hide-trace", "fde-phdr", "fde-registry"]
+default = ["unwinder", "dwarf-expr", "hide-trace", "fde-phdr-dl", "fde-registry"]
 
 [profile.dev]
 # Must be turned on due to Rust bug https://github.com/rust-lang/rust/issues/50007

src/unwinder/find_fde/phdr.rs

@@ -5,12 +5,12 @@ use core::ffi::c_void;
 use core::mem;
 use core::slice;
 use gimli::{BaseAddresses, EhFrame, EhFrameHdr, NativeEndian, UnwindSection};
-use libc::{dl_iterate_phdr, dl_phdr_info, PT_DYNAMIC, PT_GNU_EH_FRAME, PT_LOAD};
+use libc::{PT_DYNAMIC, PT_GNU_EH_FRAME, PT_LOAD};
 
-struct CallbackData {
-    pc: usize,
-    result: Option<FDESearchResult>,
-}
+#[cfg(target_pointer_width = "32")]
+use libc::Elf32_Phdr as Elf_Phdr;
+#[cfg(target_pointer_width = "64")]
+use libc::Elf64_Phdr as Elf_Phdr;
 
 pub struct PhdrFinder(());
 
@@ -20,32 +20,76 @@ pub fn get_finder() -> &'static PhdrFinder {
 
 impl super::FDEFinder for PhdrFinder {
     fn find_fde(&self, pc: usize) -> Option<FDESearchResult> {
-        let mut data = CallbackData { pc, result: None };
-        unsafe { dl_iterate_phdr(Some(phdr_callback), &mut data as *mut CallbackData as _) };
-        data.result
+        #[cfg(feature = "fde-phdr-aux")]
+        if let Some(v) = search_aux_phdr(pc) {
+            return Some(v);
+        }
+        #[cfg(feature = "fde-phdr-dl")]
+        if let Some(v) = search_dl_phdr(pc) {
+            return Some(v);
+        }
+        None
     }
 }
 
-unsafe extern "C" fn phdr_callback(
-    info: *mut dl_phdr_info,
-    _size: usize,
-    data: *mut c_void,
-) -> c_int {
+#[cfg(feature = "fde-phdr-aux")]
+fn search_aux_phdr(pc: usize) -> Option<FDESearchResult> {
+    use libc::{getauxval, AT_PHDR, AT_PHNUM, PT_PHDR};
+
     unsafe {
-        let data = &mut *(data as *mut CallbackData);
-        let phdrs = slice::from_raw_parts((*info).dlpi_phdr, (*info).dlpi_phnum as usize);
+        let phdr = getauxval(AT_PHDR) as *const Elf_Phdr;
+        let phnum = getauxval(AT_PHNUM) as usize;
+        let phdrs = slice::from_raw_parts(phdr, phnum);
+        // With known address of PHDR, we can calculate the base address in reverse.
+        let base =
+            phdrs.as_ptr() as usize - phdrs.iter().find(|x| x.p_type == PT_PHDR)?.p_vaddr as usize;
+        search_phdr(phdrs, base, pc)
+    }
+}
+
+#[cfg(feature = "fde-phdr-dl")]
+fn search_dl_phdr(pc: usize) -> Option<FDESearchResult> {
+    use libc::{dl_iterate_phdr, dl_phdr_info};
 
+    struct CallbackData {
+        pc: usize,
+        result: Option<FDESearchResult>,
+    }
+
+    unsafe extern "C" fn phdr_callback(
+        info: *mut dl_phdr_info,
+        _size: usize,
+        data: *mut c_void,
+    ) -> c_int {
+        unsafe {
+            let data = &mut *(data as *mut CallbackData);
+            let phdrs = slice::from_raw_parts((*info).dlpi_phdr, (*info).dlpi_phnum as usize);
+            if let Some(v) = search_phdr(phdrs, (*info).dlpi_addr as _, data.pc) {
+                data.result = Some(v);
+                return 1;
+            }
+            0
+        }
+    }
+
+    let mut data = CallbackData { pc, result: None };
+    unsafe { dl_iterate_phdr(Some(phdr_callback), &mut data as *mut CallbackData as _) };
+    data.result
+}
+
+fn search_phdr(phdrs: &[Elf_Phdr], base: usize, pc: usize) -> Option<FDESearchResult> {
+    unsafe {
         let mut text = None;
         let mut eh_frame_hdr = None;
         let mut dynamic = None;
 
         for phdr in phdrs {
-            let start = (*info).dlpi_addr + phdr.p_vaddr;
+            let start = base + phdr.p_vaddr as usize;
             match phdr.p_type {
                 PT_LOAD => {
-                    let end = start + phdr.p_memsz;
+                    let end = start + phdr.p_memsz as usize;
                     let range = start..end;
-                    if range.contains(&(data.pc as _)) {
+                    if range.contains(&pc) {
                         text = Some(range);
                     }
                 }
@@ -59,15 +103,8 @@ unsafe extern "C" fn phdr_callback(
             }
         }
 
-        let text = match text {
-            Some(v) => v,
-            None => return 0,
-        };
-
-        let eh_frame_hdr = match eh_frame_hdr {
-            Some(v) => v,
-            None => return 0,
-        };
+        let text = text?;
+        let eh_frame_hdr = eh_frame_hdr?;
 
         let mut bases = BaseAddresses::default()
             .set_eh_frame_hdr(eh_frame_hdr as _)
@@ -95,11 +132,8 @@ unsafe extern "C" fn phdr_callback(
             get_unlimited_slice(eh_frame_hdr as usize as _),
             NativeEndian,
         )
-        .parse(&bases, mem::size_of::<usize>() as _);
-        let eh_frame_hdr = match eh_frame_hdr {
-            Ok(v) => v,
-            Err(_) => return 0,
-        };
+        .parse(&bases, mem::size_of::<usize>() as _)
+        .ok()?;
 
         let eh_frame = deref_pointer(eh_frame_hdr.eh_frame_ptr());
         bases = bases.set_eh_frame(eh_frame as _);
@@ -108,27 +142,25 @@ unsafe extern "C" fn phdr_callback(
         // Use binary search table for address if available.
         if let Some(table) = eh_frame_hdr.table() {
             if let Ok(fde) =
-                table.fde_for_address(&eh_frame, &bases, data.pc as _, EhFrame::cie_from_offset)
+                table.fde_for_address(&eh_frame, &bases, pc as _, EhFrame::cie_from_offset)
             {
-                data.result = Some(FDESearchResult {
+                return Some(FDESearchResult {
                     fde,
                     bases,
                     eh_frame,
                 });
-                return 1;
             }
         }
 
         // Otherwise do the linear search.
-        if let Ok(fde) = eh_frame.fde_for_address(&bases, data.pc as _, EhFrame::cie_from_offset) {
-            data.result = Some(FDESearchResult {
+        if let Ok(fde) = eh_frame.fde_for_address(&bases, pc as _, EhFrame::cie_from_offset) {
+            return Some(FDESearchResult {
                 fde,
                 bases,
                 eh_frame,
             });
-            return 1;
         }
 
-        0
+        None
     }
 }