Fall back to dladdr on Unix in more places

Currently CoreSymbolication will fall back to `dladdr` but this also
applies the same logic to the `libbacktrace` symbolication strategy
since libbacktrace (especially on OSX) can't always get symbol name
information. Instead these platforms will all fall back to `dladdr` if
no symbol information is learned from libbacktrace.

This involved some refactoring internally since all invocations calling
the `dladdr` function are now shared instead of having three separate
ones throughout.

Author: alexcrichton

src/symbolize/coresymbolication.rs

@@ -29,9 +29,10 @@ use core::mem;
 use core::ptr;
 use core::slice;
 
-use libc::{self, c_char, c_int, Dl_info};
+use libc::{self, c_char, c_int};
 
 use symbolize::ResolveWhat;
+use symbolize::dladdr;
 use types::{c_void, BytesOrWideString};
 use SymbolName;
 
@@ -55,14 +56,14 @@ pub enum Symbol {
         name: *const c_char,
         addr: *mut c_void,
     },
-    Dladdr(Dl_info),
+    Dladdr(dladdr::Symbol),
 }
 
 impl Symbol {
     pub fn name(&self) -> Option<SymbolName> {
         let name = match *self {
             Symbol::Core { name, .. } => name,
-            Symbol::Dladdr(ref info) => info.dli_sname,
+            Symbol::Dladdr(ref info) => return info.name(),
         };
         if name.is_null() {
             None
@@ -77,7 +78,7 @@ impl Symbol {
     pub fn addr(&self) -> Option<*mut c_void> {
         match *self {
             Symbol::Core { addr, .. } => Some(addr),
-            Symbol::Dladdr(ref info) => Some(info.dli_saddr as *mut _),
+            Symbol::Dladdr(ref info) => info.addr(),
         }
     }
 
@@ -269,10 +270,9 @@ pub unsafe fn resolve(what: ResolveWhat, cb: &mut FnMut(&super::Symbol)) {
     if try_resolve(addr, cb) {
         return;
     }
-    let mut info: Dl_info = mem::zeroed();
-    if libc::dladdr(addr as *mut _, &mut info) != 0 {
+    dladdr::resolve(addr, &mut |sym| {
         cb(&super::Symbol {
-            inner: Symbol::Dladdr(info),
-        });
-    }
+            inner: Symbol::Dladdr(sym),
+        })
+    })
 }

src/symbolize/dladdr.rs

@@ -8,63 +8,94 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Symbolication strategy using `dladdr`
-//!
-//! The `dladdr` API is available on most Unix implementations but it's quite
-//! basic, not handling inline frame information at all. Since it's so prevalent
-//! though we have an option to use it!
+//! Common support for resolving with `dladdr`, often used as a fallback if
+//! other strategies don't work.
 
-use core::{mem, slice};
+#![allow(dead_code)]
 
-use types::{BytesOrWideString, c_void};
-use libc::{self, Dl_info};
-use symbolize::ResolveWhat;
+cfg_if! {
+    if #[cfg(all(unix, not(target_os = "emscripten"), feature = "dladdr"))] {
+        use core::{mem, slice};
 
-use SymbolName;
+        use types::{BytesOrWideString, c_void};
+        use libc::{self, Dl_info};
 
-pub struct Symbol {
-    inner: Dl_info,
-}
+        use SymbolName;
+
+        pub struct Symbol {
+            inner: Dl_info,
+        }
+
+        impl Symbol {
+            pub fn name(&self) -> Option<SymbolName> {
+                if self.inner.dli_sname.is_null() {
+                    None
+                } else {
+                    let ptr = self.inner.dli_sname as *const u8;
+                    unsafe {
+                        let len = libc::strlen(self.inner.dli_sname);
+                        Some(SymbolName::new(slice::from_raw_parts(ptr, len)))
+                    }
+                }
+            }
+
+            pub fn addr(&self) -> Option<*mut c_void> {
+                Some(self.inner.dli_saddr as *mut _)
+            }
 
-impl Symbol {
-    pub fn name(&self) -> Option<SymbolName> {
-        if self.inner.dli_sname.is_null() {
-            None
-        } else {
-            let ptr = self.inner.dli_sname as *const u8;
-            unsafe {
-                let len = libc::strlen(self.inner.dli_sname);
-                Some(SymbolName::new(slice::from_raw_parts(ptr, len)))
+            pub fn filename_raw(&self) -> Option<BytesOrWideString> {
+                None
+            }
+
+            #[cfg(feature = "std")]
+            pub fn filename(&self) -> Option<&::std::path::Path> {
+                None
+            }
+
+            pub fn lineno(&self) -> Option<u32> {
+                None
             }
         }
-    }
 
-    pub fn addr(&self) -> Option<*mut c_void> {
-        Some(self.inner.dli_saddr as *mut _)
-    }
+        pub unsafe fn resolve(addr: *mut c_void, cb: &mut FnMut(Symbol)) {
+            let mut info = Symbol {
+                inner: mem::zeroed(),
+            };
+            if libc::dladdr(addr as *mut _, &mut info.inner) != 0 {
+                cb(info)
+            }
+        }
+    } else {
+        use types::{BytesOrWideString, c_void};
+        use symbolize::SymbolName;
 
-    pub fn filename_raw(&self) -> Option<BytesOrWideString> {
-        None
-    }
+        pub enum Symbol {}
 
-    #[cfg(feature = "std")]
-    pub fn filename(&self) -> Option<&::std::path::Path> {
-        None
-    }
+        impl Symbol {
+            pub fn name(&self) -> Option<SymbolName> {
+                match *self {}
+            }
 
-    pub fn lineno(&self) -> Option<u32> {
-        None
-    }
-}
+            pub fn addr(&self) -> Option<*mut c_void> {
+                match *self {}
+            }
+
+            pub fn filename_raw(&self) -> Option<BytesOrWideString> {
+                match *self {}
+            }
+
+            #[cfg(feature = "std")]
+            pub fn filename(&self) -> Option<&::std::path::Path> {
+                match *self {}
+            }
 
-pub unsafe fn resolve(what: ResolveWhat, cb: &mut FnMut(&super::Symbol)) {
-    let addr = what.address_or_ip();
-    let mut info: super::Symbol = super::Symbol {
-        inner: Symbol {
-            inner: mem::zeroed(),
-        },
-    };
-    if libc::dladdr(addr as *mut _, &mut info.inner.inner) != 0 {
-        cb(&info)
+            pub fn lineno(&self) -> Option<u32> {
+                match *self {}
+            }
+        }
+
+        pub unsafe fn resolve(addr: *mut c_void, cb: &mut FnMut(Symbol)) {
+            drop((addr, cb));
+        }
     }
 }

src/symbolize/dladdr_resolve.rs

@@ -0,0 +1,49 @@
+// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Symbolication strategy using `dladdr`
+//!
+//! The `dladdr` API is available on most Unix implementations but it's quite
+//! basic, not handling inline frame information at all. Since it's so prevalent
+//! though we have an option to use it!
+
+use types::{BytesOrWideString, c_void};
+use symbolize::{dladdr, SymbolName, ResolveWhat};
+
+pub struct Symbol(dladdr::Symbol);
+
+impl Symbol {
+    pub fn name(&self) -> Option<SymbolName> {
+        self.0.name()
+    }
+
+    pub fn addr(&self) -> Option<*mut c_void> {
+        self.0.addr()
+    }
+
+    pub fn filename_raw(&self) -> Option<BytesOrWideString> {
+        self.0.filename_raw()
+    }
+
+    #[cfg(feature = "std")]
+    pub fn filename(&self) -> Option<&::std::path::Path> {
+        self.0.filename()
+    }
+
+    pub fn lineno(&self) -> Option<u32> {
+        self.0.lineno()
+    }
+}
+
+pub unsafe fn resolve(what: ResolveWhat, cb: &mut FnMut(&Symbol)) {
+    dladdr::resolve(what.address_or_ip(), &mut |sym| {
+        cb(Symbol(sym))
+    });
+}

src/symbolize/libbacktrace.rs

@@ -36,12 +36,10 @@
 extern crate backtrace_sys as bt;
 
 use core::{ptr, slice};
-
 use libc::{self, c_char, c_int, c_void, uintptr_t};
 
-use SymbolName;
-
-use symbolize::ResolveWhat;
+use symbolize::{ResolveWhat, SymbolName};
+use symbolize::dladdr;
 use types::BytesOrWideString;
 
 pub enum Symbol {
@@ -56,6 +54,7 @@ pub enum Symbol {
         function: *const c_char,
         symname: *const c_char,
     },
+    Dladdr(dladdr::Symbol),
 }
 
 impl Symbol {
@@ -90,13 +89,15 @@ impl Symbol {
                 }
                 symbol(symname)
             }
+            Symbol::Dladdr(ref s) => s.name(),
         }
     }
 
     pub fn addr(&self) -> Option<*mut c_void> {
         let pc = match *self {
             Symbol::Syminfo { pc, .. } => pc,
             Symbol::Pcinfo { pc, .. } => pc,
+            Symbol::Dladdr(ref s) => return s.addr(),
         };
         if pc == 0 {
             None
@@ -115,6 +116,7 @@ impl Symbol {
                     Some(slice::from_raw_parts(ptr, len))
                 }
             }
+            Symbol::Dladdr(_) => None,
         }
     }
 
@@ -146,6 +148,7 @@ impl Symbol {
         match *self {
             Symbol::Syminfo { .. } => None,
             Symbol::Pcinfo { lineno, .. } => Some(lineno as u32),
+            Symbol::Dladdr(ref s) => s.lineno(),
         }
     }
 }
@@ -425,7 +428,7 @@ pub unsafe fn resolve(what: ResolveWhat, cb: &mut FnMut(&super::Symbol)) {
     // backtrace errors are currently swept under the rug
     let state = init_state();
     if state.is_null() {
-        return;
+        return dladdr_fallback(what.address_or_ip(), cb);
     }
 
     // Call the `backtrace_syminfo` API first. This is (from reading the code)
@@ -434,15 +437,33 @@ pub unsafe fn resolve(what: ResolveWhat, cb: &mut FnMut(&super::Symbol)) {
     //
     // Note that we do this since `syminfo` will consult the symbol table,
     // finding symbol names even if there's no debug information in the binary.
-    let mut syminfo_state = SyminfoState {
-        pc: symaddr,
-        cb: cb,
-    };
-    bt::backtrace_syminfo(
-        state,
-        symaddr as uintptr_t,
-        syminfo_cb,
-        error_cb,
-        &mut syminfo_state as *mut _ as *mut _,
-    );
+    let mut called = false;
+    {
+        let mut syminfo_state = SyminfoState {
+            pc: symaddr,
+            cb: &mut |sym| {
+                called = true;
+                cb(sym);
+            },
+        };
+        bt::backtrace_syminfo(
+            state,
+            symaddr as uintptr_t,
+            syminfo_cb,
+            error_cb,
+            &mut syminfo_state as *mut _ as *mut _,
+        );
+    }
+
+    if !called {
+        dladdr_fallback(what.address_or_ip(), cb);
+    }
+}
+
+unsafe fn dladdr_fallback(addr: *mut c_void, cb: &mut FnMut(&super::Symbol)) {
+    dladdr::resolve(addr, &mut |sym| {
+        cb(&super::Symbol {
+            inner: Symbol::Dladdr(sym),
+        })
+    });
 }

src/symbolize/mod.rs

@@ -405,6 +405,8 @@ cfg_if! {
     }
 }
 
+mod dladdr;
+
 cfg_if! {
     if #[cfg(all(windows, target_env = "msvc", feature = "dbghelp"))] {
         mod dbghelp;
@@ -435,9 +437,9 @@ cfg_if! {
     } else if #[cfg(all(unix,
                         not(target_os = "emscripten"),
                         feature = "dladdr"))] {
-        mod dladdr;
-        use self::dladdr::resolve as resolve_imp;
-        use self::dladdr::Symbol as SymbolImp;
+        mod dladdr_resolve;
+        use self::dladdr_resolve::resolve as resolve_imp;
+        use self::dladdr_resolve::Symbol as SymbolImp;
     } else {
         mod noop;
         use self::noop::resolve as resolve_imp;