Implement discard_wildcard_section

Fixes #19

docs/file_format/settings.md

@@ -100,6 +100,29 @@ A positive integer or `null`.
 
 `null`
 
+## `discard_wildcard_section`
+
+Toggles emitting a discard section with a wildcard (`*`) entry, essentially
+discarding every section and file that is not explicitly listed on the linker
+script.
+
+GNU LD docs for `/DISCARD/`: <https://sourceware.org/binutils/docs/ld/Output-Section-Discarding.html#index-_002fDISCARD_002f>
+
+### Example
+
+```yaml
+settings:
+  discard_wildcard_section: False
+```
+
+### Valid values
+
+Boolean.
+
+### Default value
+
+`True`
+
 ## `alloc_sections`
 
 List of allocatable sections (the ones that take ROM space).

slinky/src/linker_writer.rs

@@ -45,6 +45,17 @@ impl<'a> LinkerWriter<'a> {
     }
 
     pub fn end_sections(&mut self) {
+        if self.settings.discard_wildcard_section {
+            self.writeln("/DISCARD/ :");
+            self.begin_block();
+
+            if self.settings.discard_wildcard_section {
+                self.writeln("*(*);")
+            }
+
+            self.end_block();
+        }
+
         self.end_block();
         assert!(self.indent_level == 0);
     }

slinky/src/settings.rs

@@ -15,6 +15,8 @@ pub struct Settings {
 
     pub hardcoded_gp_value: Option<u32>,
 
+    pub discard_wildcard_section: bool,
+
     // Options passed down to each segment
     pub alloc_sections: Vec<String>,
     pub noload_sections: Vec<String>,
@@ -40,6 +42,10 @@ fn settings_hardcoded_gp_value_default() -> Option<u32> {
     None
 }
 
+fn settings_discard_wildcard_section_default() -> bool {
+    true
+}
+
 fn settings_alloc_sections_default() -> Vec<String> {
     vec![
         ".text".into(),
@@ -78,6 +84,8 @@ impl Default for Settings {
 
             hardcoded_gp_value: settings_hardcoded_gp_value_default(),
 
+            discard_wildcard_section: settings_discard_wildcard_section_default(),
+
             alloc_sections: settings_alloc_sections_default(),
             noload_sections: settings_noload_sections_default(),
 
@@ -101,6 +109,9 @@ pub(crate) struct SettingsSerial {
     #[serde(default)]
     pub hardcoded_gp_value: AbsentNullable<u32>,
 
+    #[serde(default)]
+    pub discard_wildcard_section: AbsentNullable<bool>,
+
     #[serde(default)]
     pub alloc_sections: AbsentNullable<Vec<String>>,
     #[serde(default)]
@@ -131,6 +142,11 @@ impl SettingsSerial {
             .hardcoded_gp_value
             .get_optional_nullable("hardcoded_gp_value", settings_hardcoded_gp_value_default)?;
 
+        let discard_wildcard_section = self.discard_wildcard_section.get_non_null(
+            "discard_wildcard_section",
+            settings_discard_wildcard_section_default,
+        )?;
+
         let alloc_sections = self
             .alloc_sections
             .get_non_null("alloc_sections", settings_alloc_sections_default)?;
@@ -154,6 +170,7 @@ impl SettingsSerial {
             base_path,
             linker_symbols_style,
             hardcoded_gp_value,
+            discard_wildcard_section,
             alloc_sections,
             noload_sections,
             subalign,

tests/linker_scripts/basic_example.ld

@@ -262,4 +262,8 @@ SECTIONS
     boot_ROM_END = __romPos;
     boot_ROM_SIZE = ABSOLUTE(boot_ROM_END - boot_ROM_START);
 
+    /DISCARD/ :
+    {
+        *(*);
+    }
 }

tests/linker_scripts/drmario64.ld

@@ -7475,4 +7475,8 @@ SECTIONS
     segment_tutorial_data_ROM_END = __romPos;
     segment_tutorial_data_ROM_SIZE = ABSOLUTE(segment_tutorial_data_ROM_END - segment_tutorial_data_ROM_START);
 
+    /DISCARD/ :
+    {
+        *(*);
+    }
 }

tests/linker_scripts/hardcoded_gp.ld

@@ -73,4 +73,8 @@ SECTIONS
     main_ROM_END = __romPos;
     main_ROM_SIZE = ABSOLUTE(main_ROM_END - main_ROM_START);
 
+    /DISCARD/ :
+    {
+        *(*);
+    }
 }

tests/linker_scripts/makerom_zelda_like.ld

@@ -133,4 +133,8 @@ SECTIONS
     _bootSegmentRomEnd = __romPos;
     _bootSegmentRomSize = ABSOLUTE(_bootSegmentRomEnd - _bootSegmentRomStart);
 
+    /DISCARD/ :
+    {
+        *(*);
+    }
 }