Add symbol mapping feature (#118)

This allows users to "map" (or "link") symbols with different names so that they can be compared without having to update either the target or base objects. Symbol mappings are persisted in objdiff.json, so generators will need to ensure that they're preserved when updating. (Example: d1334bb79e)

Resolves #117

objdiff-core/src/obj/read.rs

@@ -23,6 +23,7 @@ use crate::{
     obj::{
         split_meta::{SplitMeta, SPLITMETA_SECTION},
         ObjInfo, ObjReloc, ObjSection, ObjSectionKind, ObjSymbol, ObjSymbolFlagSet, ObjSymbolFlags,
+        ObjSymbolKind,
     },
     util::{read_u16, read_u32},
 };
@@ -94,6 +95,13 @@ fn to_obj_symbol(
         })
         .unwrap_or(&[]);
 
+    let kind = match symbol.kind() {
+        SymbolKind::Text => ObjSymbolKind::Function,
+        SymbolKind::Data => ObjSymbolKind::Object,
+        SymbolKind::Section => ObjSymbolKind::Section,
+        _ => ObjSymbolKind::Unknown,
+    };
+
     Ok(ObjSymbol {
         name: name.to_string(),
         demangled_name,
@@ -101,6 +109,7 @@ fn to_obj_symbol(
         section_address,
         size: symbol.size(),
         size_known: symbol.size() != 0,
+        kind,
         flags,
         addend,
         virtual_address,
@@ -173,12 +182,19 @@ fn symbols_by_section(
     result.sort_by(|a, b| a.address.cmp(&b.address).then(a.size.cmp(&b.size)));
     let mut iter = result.iter_mut().peekable();
     while let Some(symbol) = iter.next() {
-        if symbol.size == 0 {
+        if symbol.kind == ObjSymbolKind::Unknown && symbol.size == 0 {
             if let Some(next_symbol) = iter.peek() {
                 symbol.size = next_symbol.address - symbol.address;
             } else {
                 symbol.size = (section.address + section.size) - symbol.address;
             }
+            // Set symbol kind if we ended up with a non-zero size
+            if symbol.size > 0 {
+                symbol.kind = match section.kind {
+                    ObjSectionKind::Code => ObjSymbolKind::Function,
+                    ObjSectionKind::Data | ObjSectionKind::Bss => ObjSymbolKind::Object,
+                };
+            }
         }
     }
     if result.is_empty() {
@@ -196,6 +212,10 @@ fn symbols_by_section(
             section_address: 0,
             size: section.size,
             size_known: true,
+            kind: match section.kind {
+                ObjSectionKind::Code => ObjSymbolKind::Function,
+                ObjSectionKind::Data | ObjSectionKind::Bss => ObjSymbolKind::Object,
+            },
             flags: Default::default(),
             addend: 0,
             virtual_address: None,
@@ -281,6 +301,7 @@ fn find_section_symbol(
         section_address: 0,
         size: 0,
         size_known: false,
+        kind: ObjSymbolKind::Section,
         flags: Default::default(),
         addend: address as i64 - section.address() as i64,
         virtual_address: None,
@@ -568,6 +589,7 @@ fn update_combined_symbol(symbol: ObjSymbol, address_change: i64) -> Result<ObjS
         section_address: (symbol.section_address as i64 + address_change).try_into()?,
         size: symbol.size,
         size_known: symbol.size_known,
+        kind: symbol.kind,
         flags: symbol.flags,
         addend: symbol.addend,
         virtual_address: if let Some(virtual_address) = symbol.virtual_address {