add support for illumos systems (#416)

Uses dlinfo(3C) to access the current link map on illumos systems.  From
there we can construct a list of program headers for each mapping and
get the same unwinding information available on other platforms.

src/symbolize/gimli.rs

@@ -40,6 +40,7 @@ cfg_if::cfg_if! {
         target_os = "macos",
         target_os = "openbsd",
         target_os = "solaris",
+        target_os = "illumos",
     ))] {
         #[path = "gimli/mmap_unix.rs"]
         mod mmap;
@@ -359,6 +360,110 @@ cfg_if::cfg_if! {
                 bias: slide,
             })
         }
+    } else if #[cfg(target_os = "illumos")] {
+        use mystd::os::unix::prelude::*;
+        use mystd::ffi::{OsStr, CStr};
+        use object::NativeEndian;
+
+        #[cfg(target_pointer_width = "64")]
+        use object::elf::{
+            FileHeader64 as FileHeader,
+            ProgramHeader64 as ProgramHeader
+        };
+
+        type EHdr = FileHeader<NativeEndian>;
+        type PHdr = ProgramHeader<NativeEndian>;
+
+        mod elf;
+        use self::elf::Object;
+
+        #[repr(C)]
+        struct LinkMap {
+            l_addr: libc::c_ulong,
+            l_name: *const libc::c_char,
+            l_ld: *const libc::c_void,
+            l_next: *const LinkMap,
+            l_prev: *const LinkMap,
+            l_refname: *const libc::c_char,
+        }
+
+        const RTLD_SELF: *const libc::c_void = -3isize as *const libc::c_void;
+        const RTLD_DI_LINKMAP: libc::c_int = 2;
+
+        extern "C" {
+            fn dlinfo(
+                handle: *const libc::c_void,
+                request: libc::c_int,
+                p: *mut libc::c_void,
+            ) -> libc::c_int;
+        }
+
+        fn native_libraries() -> Vec<Library> {
+            let mut libs = Vec::new();
+
+            // Request the current link map from the runtime linker:
+            let map = unsafe {
+                let mut map: *const LinkMap = std::mem::zeroed();
+                if dlinfo(
+                    RTLD_SELF,
+                    RTLD_DI_LINKMAP,
+                    (&mut map) as *mut *const LinkMap as *mut libc::c_void
+                ) != 0 {
+                    return libs;
+                }
+                map
+            };
+
+            // Each entry in the link map represents a loaded object:
+            let mut l = map;
+            while !l.is_null() {
+                // Fetch the fully qualified path of the loaded object:
+                let bytes = unsafe { CStr::from_ptr((*l).l_name)}.to_bytes();
+                let name = OsStr::from_bytes(bytes).to_owned();
+
+                // The base address of the object loaded into memory:
+                let addr = unsafe { (*l).l_addr };
+
+                // Use the ELF header for this object to locate the program
+                // header:
+                let e: *const EHdr = unsafe { (*l).l_addr as *const EHdr };
+                let phoff = unsafe { (*e).e_phoff }.get(NativeEndian);
+                let phnum = unsafe { (*e).e_phnum }.get(NativeEndian);
+                let etype = unsafe { (*e).e_type }.get(NativeEndian);
+
+                let phdr: *const PHdr = (addr + phoff) as *const PHdr;
+                let phdr = unsafe {
+                    core::slice::from_raw_parts(phdr, phnum as usize)
+                };
+
+                libs.push(Library {
+                    name,
+                    segments: phdr
+                        .iter()
+                        .map(|p| {
+                            let memsz = p.p_memsz.get(NativeEndian);
+                            let vaddr = p.p_vaddr.get(NativeEndian);
+                            LibrarySegment {
+                                len: memsz as usize,
+                                stated_virtual_memory_address: vaddr as usize,
+                            }
+                        })
+                        .collect(),
+                    bias: if etype == object::elf::ET_EXEC {
+                        // Program header addresses for the base executable are
+                        // already absolute.
+                        0
+                    } else {
+                        // Other addresses are relative to the object base.
+                        addr as usize
+                    },
+                });
+
+                l = unsafe { (*l).l_next };
+            }
+
+            libs
+        }
     } else if #[cfg(all(
         any(
             target_os = "linux",