feat: implements support for the AT keyword in output sections

LINKER_SCRIPT_SUPPORT.md

@@ -50,7 +50,7 @@ end lists the features required to link the Linux kernel.
 | `OVERLAY { ... }` | ❌ | |
 | Output section type specifiers (`(NOLOAD)`, `(COPY)`, etc.) | 📅 | |
 | `FILL(value)` and `=fillexp` | 📅 | |
-| `AT(addr)` load-address specifier on output sections | 📅 | |
+| `AT(addr)` load-address specifier on output sections | ✅ | |
 | Numeric address between section name and `:` (e.g. `name 0 : { ... }`) | 🧪 | Only numeric literals are currently supported |
 | `SORT_BY_NAME(...)`, `SORT_BY_ALIGNMENT(...)`, `SORT_BY_INIT_PRIORITY(...)` | 📅 | |
 | `EXCLUDE_FILE(...)` inside input section matchers | 📅 | |
@@ -115,7 +115,7 @@ see at a glance what remains before Wild can link the kernel.
 | `OVERLAY { ... }` sections | ❌ | |
 | Output section type specifiers (`(NOLOAD)`, `(COPY)`) | 📅 | |
 | `FILL(value)` and `=fillexp` | 📅 | |
-| `AT(addr)` load-address specifier on output sections | 📅 | |
+| `AT(addr)` load-address specifier on output sections | ✅ | |
 | `>region` and `AT>region` memory region placement | 📅 | |
 | `SORT_BY_NAME(...)`, `SORT_BY_ALIGNMENT(...)`, `SORT_BY_INIT_PRIORITY(...)` | 📅 | |
 | `EXCLUDE_FILE(...)` inside input section matchers | 📅 | |

libwild/src/elf.rs

@@ -968,6 +968,7 @@ impl platform::Platform for Elf {
                 kind: d.kind,
                 min_alignment: d.min_alignment,
                 location: None,
+                load_location: None,
                 secondary_order: None,
                 phdr_name: None,
             })

libwild/src/elf_writer.rs

@@ -385,7 +385,7 @@ fn write_program_headers(
             .p_offset
             .set(e, segment_sizes.file_offset as u64);
         segment_header.p_vaddr.set(e, segment_sizes.mem_offset);
-        segment_header.p_paddr.set(e, segment_sizes.mem_offset);
+        segment_header.p_paddr.set(e, segment_sizes.lma_offset);
         segment_header
             .p_filesz
             .set(e, segment_sizes.file_size as u64);

libwild/src/layout.rs

@@ -1297,6 +1297,7 @@ pub(crate) struct OutputRecordLayout {
     pub(crate) alignment: Alignment,
     pub(crate) file_offset: usize,
     pub(crate) mem_offset: u64,
+    pub(crate) lma_offset: u64,
 }
 
 pub(crate) struct GraphResources<'data, 'scope, P: Platform> {
@@ -1603,15 +1604,19 @@ fn layout_sections<P: Platform>(
         let info = output_sections.section_infos.get(section_id);
         let mut file_offset = usize::MAX;
         let mut mem_offset = u64::MAX;
+        let mut lma_offset = u64::MAX;
         let mut file_end = 0;
         let mut mem_end = 0;
+        let mut lma_end = 0;
         let mut alignment = info.min_alignment;
 
         for part in layouts {
             file_offset = file_offset.min(part.file_offset);
             mem_offset = mem_offset.min(part.mem_offset);
+            lma_offset = lma_offset.min(part.lma_offset);
             file_end = file_end.max(part.file_offset + part.file_size);
             mem_end = mem_end.max(part.mem_offset + part.mem_size);
+            lma_end = lma_end.max(part.lma_offset + part.mem_size);
             if part.mem_size > 0 {
                 alignment = alignment.max(part.alignment);
             }
@@ -1622,6 +1627,7 @@ fn layout_sections<P: Platform>(
             alignment,
             file_offset,
             mem_offset,
+            lma_offset,
         }
     })
 }
@@ -1710,6 +1716,8 @@ fn compute_segment_layout<'data, P: Platform>(
         file_end: usize,
         mem_start: u64,
         mem_end: u64,
+        lma_start: u64,
+        lma_end: u64,
         alignment: Alignment,
     }
 
@@ -1734,6 +1742,8 @@ fn compute_segment_layout<'data, P: Platform>(
                         file_end: 0,
                         mem_start: 0,
                         mem_end: args.stack_size_override().map_or(0, |size| size.get()),
+                        lma_start: 0,
+                        lma_end: args.stack_size_override().map_or(0, |size| size.get()),
                         alignment: alignment::MIN,
                     });
                 } else {
@@ -1743,6 +1753,8 @@ fn compute_segment_layout<'data, P: Platform>(
                         file_end: 0,
                         mem_start: u64::MAX,
                         mem_end: 0,
+                        lma_start: u64::MAX,
+                        lma_end: 0,
                         alignment: alignment::MIN,
                     });
                 }
@@ -1795,12 +1807,16 @@ fn compute_segment_layout<'data, P: Platform>(
 
                         rec.file_start = rec.file_start.min(section_layout.file_offset);
                         rec.mem_start = rec.mem_start.min(section_layout.mem_offset);
+                        rec.lma_start = rec.lma_start.min(section_layout.lma_offset);
                         rec.file_end = rec
                             .file_end
                             .max(section_layout.file_offset + section_layout.file_size);
                         rec.mem_end = rec
                             .mem_end
                             .max(section_layout.mem_offset + section_layout.mem_size);
+                        rec.lma_end = rec
+                            .lma_end
+                            .max(section_layout.lma_offset + section_layout.mem_size);
                         rec.alignment = rec.alignment.max(section_layout.alignment);
                     }
                 }
@@ -1826,6 +1842,7 @@ fn compute_segment_layout<'data, P: Platform>(
                 alignment: r.alignment,
                 file_offset: r.file_start,
                 mem_offset: r.mem_start,
+                lma_offset: r.lma_start,
             };
 
             if program_segments.is_tls_segment(id) {
@@ -4849,6 +4866,7 @@ fn layout_section_parts<'data, P: Platform>(
 
     let mut file_offset = 0;
     let mut mem_offset = expression_eval(&output_sections.base_address)?;
+    let mut lma_offset = mem_offset;
     let mut nonalloc_mem_offsets: OutputSectionMap<u64> =
         OutputSectionMap::with_size(output_sections.num_sections());
     let mut reloc_alloc_mem_offsets: OutputSectionMap<u64> =
@@ -4872,6 +4890,7 @@ fn layout_section_parts<'data, P: Platform>(
                     if let Some(expr) = pending_location.take() {
                         // The OrderEvent::SetLocation is ELF-specific only.
                         mem_offset = expression_eval(&expr)?;
+                        lma_offset = mem_offset;
                         file_offset =
                             segment_alignment.align_modulo(mem_offset, file_offset as u64) as usize;
                     } else {
@@ -4882,6 +4901,12 @@ fn layout_section_parts<'data, P: Platform>(
                             &mut file_offset,
                             &mut mem_offset,
                         );
+                        P::align_load_segment_start(
+                            segment_def,
+                            segment_alignment,
+                            &mut file_offset,
+                            &mut lma_offset,
+                        );
                     }
                 }
             }
@@ -4897,6 +4922,11 @@ fn layout_section_parts<'data, P: Platform>(
                 if let Some(ref expr) = section_info.location {
                     mem_offset = expression_eval(expr)?;
                 }
+                if let Some(ref expr) = section_info.load_location {
+                    lma_offset = expression_eval(expr)?;
+                } else {
+                    lma_offset = mem_offset;
+                }
 
                 records_out[part_id_range.clone()]
                     .iter_mut()
@@ -4939,11 +4969,13 @@ fn layout_section_parts<'data, P: Platform>(
                                     alignment,
                                     file_offset,
                                     mem_offset: part_mem_offset,
+                                    lma_offset: part_mem_offset,
                                 };
 
                                 file_offset += file_size;
                             } else {
                                 mem_offset = alignment.align_up(mem_offset);
+                                lma_offset = alignment.align_up(lma_offset);
 
                                 let file_size = if output_sections.has_data_in_file(merge_target) {
                                     mem_size as usize
@@ -4957,10 +4989,12 @@ fn layout_section_parts<'data, P: Platform>(
                                     alignment,
                                     file_offset,
                                     mem_offset,
+                                    lma_offset,
                                 };
 
                                 file_offset += file_size;
                                 mem_offset += mem_size;
+                                lma_offset += mem_size;
                             }
                         } else {
                             let section_id = part_id.output_section_id();
@@ -4975,6 +5009,7 @@ fn layout_section_parts<'data, P: Platform>(
                                 alignment,
                                 file_offset,
                                 mem_offset,
+                                lma_offset: mem_offset,
                             };
                             file_offset += mem_size as usize;
                         }

libwild/src/layout_rules.rs

@@ -228,6 +228,7 @@ impl<'data> LayoutRulesBuilder<'data> {
                                 SectionName(sec.output_section_name),
                                 min_alignment,
                                 section_location,
+                                sec.at_address.clone(),
                                 sec.phdr,
                             );
                             current_section_id = Some(primary_section_id);

libwild/src/linker_script.rs

@@ -105,6 +105,7 @@ pub(crate) struct Section<'a> {
     pub(crate) alignment: Option<Alignment>,
     pub(crate) start_address_expression: Option<Expression<'a>>,
     pub(crate) phdr: Option<&'a [u8]>,
+    pub(crate) at_address: Option<Expression<'a>>,
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
@@ -1063,9 +1064,14 @@ fn parse_section_command<'input>(
     skip_comments_and_whitespace(input)?;
 
     let mut alignment = None;
+    let mut at_address = None;
 
     while !input.starts_with(b"{") {
-        alignment = Some(parse_alignment.parse_next(input)?);
+        if opt("AT").parse_next(input)?.is_some() {
+            at_address = Some(parse_at_address.parse_next(input)?);
+        } else {
+            alignment = Some(parse_alignment.parse_next(input)?);
+        }
     }
 
     '{'.parse_next(input)?;
@@ -1089,6 +1095,7 @@ fn parse_section_command<'input>(
         alignment,
         start_address_expression,
         phdr,
+        at_address,
     }))
 }
 
@@ -1107,6 +1114,17 @@ fn parse_alignment(input: &mut &BStr) -> winnow::Result<Alignment> {
     Ok(alignment)
 }
 
+fn parse_at_address<'input>(input: &mut &'input BStr) -> winnow::Result<Expression<'input>> {
+    skip_comments_and_whitespace(input)?;
+    '('.parse_next(input)?;
+    skip_comments_and_whitespace(input)?;
+    let address = parse_expression.parse_next(input)?;
+    skip_comments_and_whitespace(input)?;
+    ')'.parse_next(input)?;
+    skip_comments_and_whitespace(input)?;
+    Ok(address)
+}
+
 fn parse_contents_command<'input>(
     input: &mut &'input BStr,
 ) -> winnow::Result<ContentsCommand<'input>> {
@@ -1416,6 +1434,7 @@ mod tests {
                 alignment: None,
                 start_address_expression: None,
                 phdr: None,
+                at_address: None,
             }),
         );
     }
@@ -1434,6 +1453,7 @@ mod tests {
                 alignment: Some(Alignment::new(8).unwrap()),
                 start_address_expression: Some(Expression::Number(0)),
                 phdr: None,
+                at_address: None,
             }),
         );
     }
@@ -1490,6 +1510,7 @@ mod tests {
                                 alignment: Some(Alignment::new(8).unwrap()),
                                 start_address_expression: None,
                                 phdr: None,
+                                at_address: None,
                             }),
                         ],
                     }),
@@ -1627,6 +1648,7 @@ mod tests {
                 alignment: None,
                 start_address_expression: None,
                 phdr: None,
+                at_address: None,
             }),
         );
     }
@@ -1645,6 +1667,7 @@ mod tests {
                 alignment: None,
                 start_address_expression: None,
                 phdr: None,
+                at_address: None,
             }),
         );
     }
@@ -1663,6 +1686,7 @@ mod tests {
                 alignment: None,
                 start_address_expression: None,
                 phdr: None,
+                at_address: None,
             }),
         );
     }
@@ -1689,6 +1713,7 @@ mod tests {
                             alignment: None,
                             start_address_expression: None,
                             phdr: None,
+                            at_address: None,
                         })],
                     }),
                     Command::Assert(AssertCommand {
@@ -1726,6 +1751,7 @@ mod tests {
                             alignment: None,
                             start_address_expression: None,
                             phdr: None,
+                            at_address: None,
                         }),
                         SectionCommand::Assert(AssertCommand {
                             expression: Expression::LessThan(

libwild/src/macho.rs

@@ -1189,6 +1189,7 @@ impl platform::Platform for MachO {
                 kind: d.kind,
                 min_alignment: d.min_alignment,
                 location: None,
+                load_location: None,
                 secondary_order: None,
                 phdr_name: None,
             })

libwild/src/output_section_id.rs

@@ -503,6 +503,7 @@ pub(crate) struct SectionOutputInfo<'data, P: Platform> {
     pub(crate) section_attributes: P::SectionAttributes,
     pub(crate) min_alignment: Alignment,
     pub(crate) location: Option<linker_script::Expression<'data>>,
+    pub(crate) load_location: Option<linker_script::Expression<'data>>,
     pub(crate) secondary_order: Option<SecondaryOrder>,
     pub(crate) phdr_name: Option<&'data [u8]>,
 }
@@ -642,7 +643,8 @@ impl<'data, P: Platform> OutputSections<'data, P> {
             let location = args
                 .start_address_for_section(custom.name)
                 .map(linker_script::Expression::Number);
-            let section_id = self.add_named_section(custom.name, custom.alignment, location, None);
+            let section_id =
+                self.add_named_section(custom.name, custom.alignment, location, None, None);
 
             section_part_ids[custom.index.0] = section_id.part_id_with_alignment(custom.alignment);
         }
@@ -669,6 +671,7 @@ impl<'data, P: Platform> OutputSections<'data, P> {
         name: SectionName<'data>,
         min_alignment: Alignment,
         location: Option<linker_script::Expression<'data>>,
+        load_location: Option<linker_script::Expression<'data>>,
         phdr_name: Option<&'data [u8]>,
     ) -> OutputSectionId {
         *self.custom_by_name.entry(name).or_insert_with(|| {
@@ -679,6 +682,7 @@ impl<'data, P: Platform> OutputSections<'data, P> {
                 section_attributes: Default::default(),
                 min_alignment,
                 location,
+                load_location,
                 secondary_order: None,
                 phdr_name,
             })
@@ -691,12 +695,15 @@ impl<'data, P: Platform> OutputSections<'data, P> {
         min_alignment: Alignment,
         secondary_order: Option<SecondaryOrder>,
     ) -> OutputSectionId {
-        let section_attributes = self.section_infos.get(primary_id).section_attributes;
+        let primary_info = self.section_infos.get(primary_id);
+        let section_attributes = primary_info.section_attributes;
+        let load_location = primary_info.load_location.clone();
         self.section_infos.add_new(SectionOutputInfo {
             kind: SectionKind::Secondary(primary_id),
             section_attributes,
             min_alignment,
             location: None,
+            load_location,
             secondary_order,
             phdr_name: None,
         })
@@ -949,6 +956,7 @@ impl<'data, P: Platform> OutputSections<'data, P> {
                 crate::alignment::MIN,
                 None,
                 None,
+                None,
             )
         };
         add_name("ro");

libwild/src/wasm.rs

@@ -1593,6 +1593,7 @@ impl platform::Platform for Wasm {
                 kind: d.kind,
                 min_alignment: crate::alignment::MIN,
                 location: None,
+                load_location: None,
                 secondary_order: None,
                 phdr_name: None,
             })