Remove dladdr fallback and implementation (rust-lang#317)

* Remove dladdr fallback and implementation

This has been present for a very long time but I believe this has never
actually been that necessary. Non-MSVC platforms all use libbacktrace by
default, and libbacktrace will consult symbol tables of object files to
do what `dladdr` does, just inside of libbacktrace. Additionally gimli
implements the same logic. I believe that this means that `dladdr` isn't
necessary for resolving any symbols since our other strategies should
already be doing everything for us.

This commit makes the feature defunkt and otherwise removes the various
forms of fallback to dladdr.

* Switch to the `object` crate for object parsing

This commit switches the gimli feature from the `goblin` crate to the
`object` crate for parsing object files. The main motivation here is
trimming the dependencies of the `gimli-symbolize` feature to a bare
minimum. The `object` crate itself has no dependencies now and should be
a relatively easy drop-in replacement for the `goblin` crate.

* Parse fat libraries on macOS

This commit updates the object parsing code for macOS to support fat
libraries. This enables gimli to symbolize addresses coming from system
libraries which are currently installed frequently as fat libraries.

Closes rust-lang#319

* Fix macOS symbolication of system libraries

This commit fixes an issue where symbolication of system libraries
didn't work on macOS. Symbolication through the symbol table was always
off by a slide amount for the library. It's not entirely clear why this
kept happening or what was going on, but some poking in LLDB's source
revealed a way we can differentiate and figure out what addresses need
to be looked up in the symbol table. Some more information is contained
in the comments of the commit itself.

Closes rust-lang#318

Co-authored-by: Philip Craig <philipjcraig@gmail.com>

Author: alexcrichton

Cargo.toml

@@ -35,7 +35,12 @@ cpp_demangle = { default-features = false, version = "0.2.3", optional = true }
 
 # Optional dependencies enabled through the `gimli-symbolize` feature
 addr2line = { version = "0.11.0", optional = true, default-features = false, features = ['std'] }
-goblin = { version = "0.2", optional = true, default-features = false, features = ['elf32', 'elf64', 'mach32', 'mach64', 'pe32', 'pe64', 'std'] }
+
+[dependencies.object]
+version = "0.19"
+optional = true
+default-features = false
+features = ['read_core', 'elf', 'macho', 'pe']
 
 [target.'cfg(windows)'.dependencies]
 winapi = { version = "0.3.3", optional = true }
@@ -49,7 +54,7 @@ winapi = { version = "0.3.3", optional = true }
 # Note that not all features are available on all platforms, so even though a
 # feature is enabled some other feature may be used instead.
 [features]
-default = ["std", "libunwind", "libbacktrace", "dladdr", "dbghelp"]
+default = ["std", "libunwind", "libbacktrace", "dbghelp"]
 
 # Include std support.
 std = []
@@ -81,17 +86,13 @@ kernel32 = []
 #   can also provide filename/line number information if debuginfo is
 #   compiled in. This library currently only primarily works on unixes that
 #   are not OSX, however.
-# - dladdr: this feature uses the dladdr(3) function (a glibc extension) to
-#   resolve symbol names. This is fairly unreliable on linux, but works well
-#   enough on OSX.
 # - gimli-symbolize: use the `gimli-rs/addr2line` crate to symbolicate
 #   addresses into file, line, and name using DWARF debug information. At
 #   the moment, this is only possible when targetting Linux, since macOS
 #   splits DWARF out into a separate object file. Enabling this feature
 #   means one less C dependency.
 libbacktrace = ["backtrace-sys/backtrace-sys"]
-dladdr = []
-gimli-symbolize = ["addr2line", "goblin"]
+gimli-symbolize = ["addr2line", "object"]
 
 #=======================================
 # Methods of serialization
@@ -105,6 +106,7 @@ serialize-serde = ["serde"]
 #
 # Only here for backwards compatibility purposes, they do nothing now.
 coresymbolication = []
+dladdr = []
 
 #=======================================
 # Internal features for testing and such.

crates/without_debuginfo/Cargo.toml

@@ -12,9 +12,6 @@ features = [
   'libunwind',
   'dbghelp',
 
-  # Allow fallback to dladdr
-  'dladdr',
-
   # Yes, we have `std`
   'std',
 ]