Add option to control emission of noload segment

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- Add option to control emission of `noload` segment.
+
 ### Changed
 
 - Include `.symtab` and `.strtab` in default value of `sections_allowlist_extra`
@@ -15,6 +17,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     explicitly on the linker script.
 - Add `.got` to the default list of discarded sections.
 - Simplify the formatting used for extra sections.
+- `alloc_sections` and `noload_sections` sections now accept `null` values.
+  - This allows to avoid emitting those sections completely for a given segment
+    or globally.
+  - The main difference between using `null` and an empty list is `null` will
+    not produce linker symbol nor the section itself in the generated linker
+    script, while the empty list would generate the starting and ending linker
+    symbols and the section with no files.
 
 ## [0.3.0] - 2024-08-17
 

docs/file_format/segments.md

@@ -295,6 +295,10 @@ segment.
 The sections from this list will be emitted for each file in the specified
 order.
 
+A `null` value can be used to signal that no allocatable sections should be
+emitted for this segment. Setting to `null` will avoid emitting linker symbols
+for allocatable sections too.
+
 This allows to override the global settings in case a specific segment has
 an order different than the global one. See
 [settings.md#alloc_sections](settings.md#alloc_sections) for more info.
@@ -308,7 +312,7 @@ settings:
 
 ### Valid values
 
-List of strings.
+List of strings or `null`.
 
 ### Default value
 
@@ -322,6 +326,9 @@ segment.
 The sections from this list will be emitted for each file in the specified
 order.
 
+A `null` value can be used to signal that no noload sections should be emitted.
+Setting to `null` will avoid emitting linker symbols for noload sections too.
+
 This allows to override the global settings in case a specific segment has
 an order different than the global one. See
 [settings.md#noload_sections](settings.md#noload_sections) for more info.
@@ -335,7 +342,7 @@ settings:
 
 ### Valid values
 
-List of strings.
+List of strings or `null`.
 
 ### Default value
 

docs/file_format/settings.md

@@ -536,6 +536,10 @@ List of allocatable sections (the ones that take ROM space).
 The sections from this list will be emitted for each file in the specified
 order.
 
+A `null` value can be used to signal that no allocatable sections should be
+emitted. Setting to `null` will avoid emitting linker symbols for allocatable
+sections too.
+
 This option can be overriden per segment, see
 [segments.md#alloc_sections](segments.md#alloc_sections) for more info.
 
@@ -548,7 +552,7 @@ settings:
 
 ### Valid values
 
-List of strings.
+List of strings or `null`.
 
 ### Default value
 
@@ -561,6 +565,9 @@ List of noload sections (the ones that don't take ROM space).
 The sections from this list will be emitted for each file in the specified
 order.
 
+A `null` value can be used to signal that no noload sections should be emitted.
+Setting to `null` will avoid emitting linker symbols for noload sections too.
+
 This option can be overriden per segment, see
 [segments.md#noload_sections](segments.md#noload_sections) for more info.
 
@@ -573,7 +580,7 @@ settings:
 
 ### Valid values
 
-List of strings.
+List of strings or `null`.
 
 ### Default value
 

slinky/src/linker_writer.rs

@@ -554,12 +554,16 @@ impl LinkerWriter<'_> {
             .write_linker_symbol(&main_seg_sym_start, &format!("ADDR(.{})", segment.name));
 
         // Emit alloc segment
-        self.write_segment(segment, &segment.alloc_sections, false)?;
+        if let Some(alloc_sections) = &segment.alloc_sections {
+            self.write_segment(segment, alloc_sections, false)?;
+        }
 
         self.buffer.write_empty_line();
 
         // Emit noload segment
-        self.write_segment(segment, &segment.noload_sections, true)?;
+        if let Some(noload_sections) = &segment.noload_sections {
+            self.write_segment(segment, noload_sections, true)?;
+        }
 
         self.buffer.write_empty_line();
 
@@ -612,12 +616,16 @@ impl LinkerWriter<'_> {
         }
 
         // Emit alloc segment
-        self.write_single_segment(segment, &segment.alloc_sections, false)?;
+        if let Some(alloc_sections) = &segment.alloc_sections {
+            self.write_single_segment(segment, alloc_sections, false)?;
+        }
 
         self.buffer.write_empty_line();
 
         // Emit noload segment
-        self.write_single_segment(segment, &segment.noload_sections, true)?;
+        if let Some(noload_sections) = &segment.noload_sections {
+            self.write_single_segment(segment, noload_sections, true)?;
+        }
 
         self.buffer.write_empty_line();
 

slinky/src/segment.rs

@@ -10,7 +10,7 @@ use crate::{
     file_info::{FileInfo, FileInfoSerial},
     gp_info::{GpInfo, GpInfoSerial},
     traits::Serial,
-    EscapedPath, KeepSections, RuntimeSettings, Settings, SlinkyError,
+    utils, EscapedPath, KeepSections, RuntimeSettings, Settings, SlinkyError,
 };
 
 #[derive(PartialEq, Debug, Clone)]
@@ -48,8 +48,8 @@ pub struct Segment {
     pub exclude_if_all: Vec<(String, String)>,
 
     // The default value of the following members come from Settings
-    pub alloc_sections: Vec<String>,
-    pub noload_sections: Vec<String>,
+    pub alloc_sections: Option<Vec<String>>,
+    pub noload_sections: Option<Vec<String>>,
 
     pub subalign: Option<u32>,
     pub segment_start_align: Option<u32>,
@@ -293,13 +293,15 @@ impl Serial for SegmentSerial {
 
         let alloc_sections = self
             .alloc_sections
-            .get_non_null("alloc_sections", || settings.alloc_sections.clone())?;
+            .get_optional_nullable("alloc_sections", || settings.alloc_sections.clone())?;
         let noload_sections = self
             .noload_sections
-            .get_non_null("noload_sections", || settings.noload_sections.clone())?;
+            .get_optional_nullable("noload_sections", || settings.noload_sections.clone())?;
 
         if let Some(gp) = &gp_info {
-            if !alloc_sections.contains(&gp.section) && !noload_sections.contains(&gp.section) {
+            if utils::is_none_or(alloc_sections.as_ref(), |s| !s.contains(&gp.section))
+                && utils::is_none_or(noload_sections.as_ref(), |s| !s.contains(&gp.section))
+            {
                 return Err(SlinkyError::MissingSectionForSegment {
                     field_name: Cow::from("gp_info"),
                     section: Cow::from(gp_info.unwrap().section),

slinky/src/settings.rs

@@ -34,8 +34,8 @@ pub struct Settings {
     pub partial_build_segments_folder: Option<PathBuf>,
 
     // Options passed down to each segment
-    pub alloc_sections: Vec<String>,
-    pub noload_sections: Vec<String>,
+    pub alloc_sections: Option<Vec<String>>,
+    pub noload_sections: Option<Vec<String>>,
 
     pub subalign: Option<u32>,
     pub segment_start_align: Option<u32>,
@@ -120,22 +120,22 @@ const fn settings_default_partial_build_segments_folder() -> Option<PathBuf> {
     None
 }
 
-fn settings_default_alloc_sections() -> Vec<String> {
-    vec![
+fn settings_default_alloc_sections() -> Option<Vec<String>> {
+    Some(vec![
         ".text".into(),
         ".data".into(),
         ".rodata".into(),
         ".sdata".into(),
-    ]
+    ])
 }
 
-fn settings_default_noload_sections() -> Vec<String> {
-    vec![
+fn settings_default_noload_sections() -> Option<Vec<String>> {
+    Some(vec![
         ".sbss".into(),
         ".scommon".into(),
         ".bss".into(),
         "COMMON".into(),
-    ]
+    ])
 }
 
 const fn settings_default_subalign() -> Option<u32> {
@@ -417,10 +417,10 @@ impl SettingsSerial {
 
         let alloc_sections = self
             .alloc_sections
-            .get_non_null("alloc_sections", settings_default_alloc_sections)?;
+            .get_optional_nullable("alloc_sections", settings_default_alloc_sections)?;
         let noload_sections = self
             .noload_sections
-            .get_non_null("noload_sections", settings_default_noload_sections)?;
+            .get_optional_nullable("noload_sections", settings_default_noload_sections)?;
 
         let subalign = self
             .subalign
@@ -488,6 +488,7 @@ impl SettingsSerial {
 
             alloc_sections,
             noload_sections,
+
             subalign,
             segment_start_align,
             segment_end_align,

slinky/src/utils.rs

@@ -37,3 +37,13 @@ pub(crate) fn create_file_and_parents(path: &Path) -> Result<File, SlinkyError>
         }),
     }
 }
+
+pub(crate) fn is_none_or<T, F>(val: Option<&T>, f: F) -> bool
+where
+    F: FnOnce(&T) -> bool,
+{
+    match val {
+        None => true,
+        Some(x) => f(x),
+    }
+}

tests/test_cases/null_sections.h

@@ -0,0 +1,83 @@
+#ifndef HEADER_SYMBOLS_H
+#define HEADER_SYMBOLS_H
+
+extern char boot_ROM_START[];
+extern char boot_VRAM[];
+extern char boot_alloc_VRAM[];
+extern char boot_TEXT_START[];
+extern char boot_TEXT_END[];
+extern char boot_TEXT_SIZE[];
+extern char boot_DATA_START[];
+extern char boot_DATA_END[];
+extern char boot_DATA_SIZE[];
+extern char boot_RODATA_START[];
+extern char boot_RODATA_END[];
+extern char boot_RODATA_SIZE[];
+extern char boot_SDATA_START[];
+extern char boot_SDATA_END[];
+extern char boot_SDATA_SIZE[];
+extern char boot_alloc_VRAM_END[];
+extern char boot_alloc_VRAM_SIZE[];
+extern char boot_noload_VRAM[];
+extern char boot_SBSS_START[];
+extern char boot_SBSS_END[];
+extern char boot_SBSS_SIZE[];
+extern char boot_SCOMMON_START[];
+extern char boot_SCOMMON_END[];
+extern char boot_SCOMMON_SIZE[];
+extern char boot_BSS_START[];
+extern char boot_BSS_END[];
+extern char boot_BSS_SIZE[];
+extern char bootCOMMON_START[];
+extern char bootCOMMON_END[];
+extern char bootCOMMON_SIZE[];
+extern char boot_noload_VRAM_END[];
+extern char boot_noload_VRAM_SIZE[];
+extern char boot_VRAM_END[];
+extern char boot_VRAM_SIZE[];
+extern char boot_ROM_END[];
+extern char boot_ROM_SIZE[];
+extern char buffers_ROM_START[];
+extern char buffers_VRAM[];
+extern char buffers_noload_VRAM[];
+extern char buffers_SBSS_START[];
+extern char buffers_SBSS_END[];
+extern char buffers_SBSS_SIZE[];
+extern char buffers_SCOMMON_START[];
+extern char buffers_SCOMMON_END[];
+extern char buffers_SCOMMON_SIZE[];
+extern char buffers_BSS_START[];
+extern char buffers_BSS_END[];
+extern char buffers_BSS_SIZE[];
+extern char buffersCOMMON_START[];
+extern char buffersCOMMON_END[];
+extern char buffersCOMMON_SIZE[];
+extern char buffers_noload_VRAM_END[];
+extern char buffers_noload_VRAM_SIZE[];
+extern char buffers_VRAM_END[];
+extern char buffers_VRAM_SIZE[];
+extern char buffers_ROM_END[];
+extern char buffers_ROM_SIZE[];
+extern char assets_ROM_START[];
+extern char assets_VRAM[];
+extern char assets_alloc_VRAM[];
+extern char assets_TEXT_START[];
+extern char assets_TEXT_END[];
+extern char assets_TEXT_SIZE[];
+extern char assets_DATA_START[];
+extern char assets_DATA_END[];
+extern char assets_DATA_SIZE[];
+extern char assets_RODATA_START[];
+extern char assets_RODATA_END[];
+extern char assets_RODATA_SIZE[];
+extern char assets_SDATA_START[];
+extern char assets_SDATA_END[];
+extern char assets_SDATA_SIZE[];
+extern char assets_alloc_VRAM_END[];
+extern char assets_alloc_VRAM_SIZE[];
+extern char assets_VRAM_END[];
+extern char assets_VRAM_SIZE[];
+extern char assets_ROM_END[];
+extern char assets_ROM_SIZE[];
+
+#endif