warning for multiple definitions of symbol

3 files changed, 16 insertions, 6 deletions

diff --git a/src/linker.rs b/src/linker.rs
index b1ee0a8..f4b4237 100644
--- a/src/linker.rs
+++ b/src/linker.rs
@@ -121,6 +121,8 @@ pub enum LinkWarning {
 	RelUnsupported(u8),
 	/// relocation is too large
 	RelOOB(String, u64),
+	/// multiple definitions of a symbol
+	MultipleDefinitions(String),
 }
 
 impl fmt::Display for LinkWarning {
@@ -129,6 +131,7 @@ impl fmt::Display for LinkWarning {
 		match self {
 			RelOOB(source, offset) => write!(f, "relocation {source}+0x{offset:x} goes outside of its section (it will be ignored)."),
 			RelUnsupported(x) => write!(f, "Unsupported relocation type {x} (relocation ignored)."),
+			MultipleDefinitions(name) => write!(f, "Symbol {name} has multiple definitions. One of them will be chosen arbitrarily."),
 		}
 	}
 }
@@ -940,10 +943,13 @@ impl<'a> Linker<'a> {
 		symbol: &elf::Symbol,
 	) -> ObjectResult<()> {
 		let name = elf.symbol_name(symbol)?;
-		//		let dbg_name = name.clone();
 		let name_id = self.symbol_names.add(name);
 		let size = symbol.size;
 
+		if self.symbols.get_id_from_name(source, name_id).is_some() {
+			self.emit_warning(LinkWarning::MultipleDefinitions(elf.symbol_name(symbol)?));
+		}
+
 		let value = match symbol.value {
 			elf::SymbolValue::Undefined => None,
 			elf::SymbolValue::Absolute(n) => Some(SymbolValue::Absolute(n)),
diff --git a/src/main.rs b/src/main.rs
index 926b1e4..201b649 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,8 +1,5 @@
 /*
 @TODO:
-- what happens when a symbol has two definitions? can this happen with multiple c++ files which use the same template?
-- disable "warning: relocation XXX not in a data/text section" for .rel.eh_frame + maybe others
-	- these warnings are being generated in two places. do they need to be?
 - make executables more tiny (overlap sections, etc.)
 - generate a warning/error on position-independent object files
 - static libraries
@@ -28,7 +25,7 @@ struct Args {
 	no_std_lib: bool,
 	/// If set, the program will be linked against libstdc++.
 	///
-	/// This is needed when using the standard template library.
+	/// This is needed when using any C++ library functions.
 	#[arg(long = "stdc++", default_value_t = false)]
 	std_cpp: bool,
 	/// Output executable path.
diff --git a/test.c b/test.c
index 1ec95d1..83253e0 100644
--- a/test.c
+++ b/test.c
@@ -1,6 +1,13 @@
+// temporary test file
+
 #include<stdio.h>
 #include <stdlib.h>
+int f() {
+	return 7;
+}
+
+
 void entry(void) {
-	printf("hi\n");
+	printf("%d\n", f());
 	exit(0);
 }