Support Linkle's DWARF implementation for target_env = "devkita64" (#361

)

* Disable libbacktrace on DevkitA64

* Force noop symbolizer on DevkitA64 (for now)

* Add support for linkle's DWARF format to gimli symbolizer

* fmt

* Address review

* Subtract bias from len, revert back to wrapping_add

* Use Vec::with_capacity in mmap_fake

* fmt

src/symbolize/gimli.rs

@@ -28,12 +28,19 @@ mod mystd {
 #[cfg(not(backtrace_in_libstd))]
 extern crate std as mystd;
 
-#[cfg(windows)]
-#[path = "gimli/mmap_windows.rs"]
-mod mmap;
-#[cfg(unix)]
-#[path = "gimli/mmap_unix.rs"]
-mod mmap;
+cfg_if::cfg_if! {
+    if #[cfg(windows)] {
+        #[path = "gimli/mmap_windows.rs"]
+        mod mmap;
+    } else if #[cfg(target_env = "devkita64")] {
+        #[path = "gimli/mmap_fake.rs"]
+        mod mmap;
+    } else {
+        #[path = "gimli/mmap_unix.rs"]
+        mod mmap;
+    }
+}
+
 mod stash;
 
 const MAPPINGS_CACHE_SIZE: usize = 4;
@@ -386,6 +393,35 @@ cfg_if::cfg_if! {
             });
             0
         }
+    } else if #[cfg(target_env = "devkita64")] {
+        // DevkitA64 doesn't natively support debug info, but the build system will place debug
+        // info at the path `romfs:/debug_info.elf`.
+        mod elf;
+        use self::elf::Object;
+
+        fn native_libraries() -> Vec<Library> {
+            extern "C" {
+                static __start__: u8;
+            }
+
+            let bias = unsafe { &__start__ } as *const u8 as usize;
+
+            let mut ret = Vec::new();
+            let mut segments = Vec::new();
+            segments.push(LibrarySegment {
+                stated_virtual_memory_address: 0,
+                len: usize::max_value() - bias,
+            });
+
+            let path = "romfs:/debug_info.elf";
+            ret.push(Library {
+                name: path.into(),
+                segments,
+                bias,
+            });
+
+            ret
+        }
     } else {
         // Everything else should use ELF, but doesn't know how to load native
         // libraries.

src/symbolize/gimli/mmap_fake.rs

@@ -0,0 +1,25 @@
+use super::{mystd::io::Read, File};
+use alloc::vec::Vec;
+use core::ops::Deref;
+
+pub struct Mmap {
+    vec: Vec<u8>,
+}
+
+impl Mmap {
+    pub unsafe fn map(mut file: &File, len: usize) -> Option<Mmap> {
+        let mut mmap = Mmap {
+            vec: Vec::with_capacity(len),
+        };
+        file.read_to_end(&mut mmap.vec).ok()?;
+        Some(mmap)
+    }
+}
+
+impl Deref for Mmap {
+    type Target = [u8];
+
+    fn deref(&self) -> &[u8] {
+        &self.vec[..]
+    }
+}