call host functions from the app

crates/linker/src/pe.rs

@@ -4,7 +4,7 @@ use memmap2::{Mmap, MmapMut};
 use object::{
     pe::{ImageImportDescriptor, ImageNtHeaders64, ImageSectionHeader, ImageThunkData64},
     read::pe::ImportTable,
-    LittleEndian as LE, SectionIndex,
+    LittleEndian as LE, RelocationTarget, SectionIndex,
 };
 use roc_collections::MutMap;
 use roc_error_macros::internal_error;
@@ -532,8 +532,8 @@ enum SectionKind {
 struct Section {
     /// File range of the section (in the app object)
     file_range: Range<usize>,
-
     kind: SectionKind,
+    relocations: MutMap<String, (u64, object::Relocation)>,
 }
 
 #[allow(dead_code)]
@@ -574,6 +574,24 @@ impl AppSections {
                 _ => continue,
             };
 
+            let mut relocations = MutMap::default();
+
+            for (offset_in_section, relocation) in section.relocations() {
+                match relocation.target() {
+                    RelocationTarget::Symbol(symbol_index) => {
+                        use object::ObjectSymbol;
+
+                        let name = file
+                            .symbol_by_index(symbol_index)
+                            .and_then(|s| s.name())
+                            .unwrap_or_default();
+
+                        relocations.insert(name.to_string(), (offset_in_section, relocation));
+                    }
+                    _ => todo!(),
+                }
+            }
+
             let (start, length) = section.file_range().unwrap();
             let file_range = start as usize..(start + length) as usize;
 
@@ -591,7 +609,11 @@ impl AppSections {
                 }
             }
 
-            let section = Section { file_range, kind };
+            let section = Section {
+                file_range,
+                kind,
+                relocations,
+            };
 
             sections.push(section);
         }
@@ -990,6 +1012,10 @@ mod test {
                 return 123456;
             }
 
+            pub export fn roc_realloc() u64 {
+                return 111111;
+            }
+
             pub fn main() !void {
                 const stdout = std.io.getStdOut().writer();
                 try stdout.print("Hello, {} {} {} {}!\n", .{roc_magic1(), roc_magic2(), roc_one, roc_three});
@@ -1002,8 +1028,11 @@ mod test {
             export const roc_one: u64 = 1;
             export const roc_three: u64 = 3;
 
+            extern fn roc_alloc() u64;
+            extern fn roc_realloc() u64;
+
             export fn roc_magic1() u64 {
-                return 42;
+                return roc_alloc() + roc_realloc();
             }
 
             export fn roc_magic2() u8 {
@@ -1107,6 +1136,18 @@ mod test {
         let file = PeFile64::parse(app.deref()).unwrap();
         let last_host_section = file.sections().nth(last_host_section_index).unwrap();
 
+        let exports: MutMap<String, i64> = file
+            .exports()
+            .unwrap()
+            .into_iter()
+            .map(|e| {
+                (
+                    String::from_utf8(e.name().to_vec()).unwrap(),
+                    (e.address() - image_base) as i64,
+                )
+            })
+            .collect();
+
         let optional_header_offset = file.dos_header().nt_headers_offset() as usize
             + std::mem::size_of::<u32>()
             + std::mem::size_of::<ImageFileHeader>();
@@ -1179,6 +1220,26 @@ mod test {
             for section in it {
                 let slice = &app_obj[section.file_range.start..section.file_range.end];
                 app[offset..][..slice.len()].copy_from_slice(slice);
+
+                for (name, (offset_in_section, relocation)) in section.relocations.iter() {
+                    let destination = exports[name];
+
+                    match relocation.kind() {
+                        object::RelocationKind::Relative => {
+                            // we implicitly only do 32-bit relocations
+                            debug_assert_eq!(relocation.size(), 32);
+
+                            let delta =
+                                destination - virtual_address as i64 - *offset_in_section as i64
+                                    + relocation.addend();
+
+                            app[offset + *offset_in_section as usize..][..4]
+                                .copy_from_slice(&(delta as i32).to_le_bytes());
+                        }
+                        _ => todo!(),
+                    }
+                }
+
                 offset += slice.len();
             }
 
@@ -1235,7 +1296,7 @@ mod test {
 
         let output = String::from_utf8_lossy(&output.stdout);
 
-        assert_eq!("Hello, 42 32 1 3!\n", output);
+        assert_eq!("Hello, 234567 32 1 3!\n", output);
     }
 
     #[ignore]
@@ -1263,6 +1324,6 @@ mod test {
 
         let output = String::from_utf8_lossy(&output.stdout);
 
-        assert_eq!("Hello, 42 32 1 3!\n", output);
+        assert_eq!("Hello, 234567 32 1 3!\n", output);
     }
 }