Merge pull request #25 from bitemyapp/parity/21-umbrella-noreloc

Order the umbrella commands and flag an anchors-only segment as ld-prime does

src/chunks/mod.rs

@@ -327,6 +327,26 @@ fn create_segment_cmd<E: Target>(ctx: &Context<E>, seg: &OutputSegment) -> Vec<u
     if seg.name == "__DATA_CONST" {
         cmd.flags = SG_READ_ONLY;
     }
+    // A segment of nothing but -add_empty_section anchors has nothing
+    // to relocate; ld-prime flags it SG_NORELOC. Only that option, not
+    // an empty section a `section$start$` boundary symbol conjured, and
+    // not an empty segment such as __PAGEZERO (no sections at all).
+    if !seg.chunks.is_empty()
+        && seg.chunks.iter().all(|&id| match id {
+            ChunkId::SectCreate(i) => {
+                let h = &ctx.sectcreate_sections[i as usize].hdr;
+                h.size == 0
+                    && ctx
+                        .args
+                        .add_empty_section
+                        .iter()
+                        .any(|(seg, sect)| seg == h.segname && sect == &h.sectname)
+            }
+            _ => false,
+        })
+    {
+        cmd.flags |= SG_NORELOC;
+    }
 
     let mut buf = to_vec(&cmd);
     for hdr in sects {
@@ -569,12 +589,6 @@ pub fn create_load_commands<E: Target>(ctx: &Context<E>) -> Vec<Vec<u8>> {
 
     if ctx.args.output_type == MH_DYLIB {
         vec.push(create_id_dylib_cmd(ctx));
-        if let Some(name) = &ctx.args.umbrella {
-            vec.push(create_string_cmd(LC_SUB_FRAMEWORK, name));
-        }
-        for client in &ctx.args.allowable_clients {
-            vec.push(create_string_cmd(LC_SUB_CLIENT, client));
-        }
     }
 
     // Chained fixups replace the classic dyld info; the export trie
@@ -608,6 +622,17 @@ pub fn create_load_commands<E: Target>(ctx: &Context<E>) -> Vec<Vec<u8>> {
         vec.push(create_load_dylib_cmd(dylib));
     }
 
+    // The umbrella commands follow the libraries, clients first, as
+    // ld-prime orders them.
+    if ctx.args.output_type == MH_DYLIB {
+        for client in &ctx.args.allowable_clients {
+            vec.push(create_string_cmd(LC_SUB_CLIENT, client));
+        }
+        if let Some(name) = &ctx.args.umbrella {
+            vec.push(create_string_cmd(LC_SUB_FRAMEWORK, name));
+        }
+    }
+
     for rpath in &ctx.args.rpaths {
         vec.push(create_string_cmd(LC_RPATH, rpath));
     }

src/macho_consts.rs

@@ -200,6 +200,7 @@ pub const BIND_SPECIAL_DYLIB_WEAK_LOOKUP: i32 = -3;
 pub const BIND_OPCODE_SET_DYLIB_SPECIAL_IMM: u8 = 0x30;
 
 // Segment flags
+pub const SG_NORELOC: u32 = 0x4;
 pub const SG_READ_ONLY: u32 = 0x10;
 
 // Bind opcodes, for the LC_DYLD_INFO bind stream. Each opcode byte holds

tests/add-empty-section.sh

@@ -9,3 +9,6 @@ $CC --ld-path=$mold -o $t/exe $t/a.o -Wl,-add_empty_section,__FOO,__foo
 
 otool -l $t/exe | grep 'segname __FOO'
 otool -l $t/exe | grep 'sectname __foo'
+# The segment of only such anchors is flagged SG_NORELOC, as ld-prime
+# flags it.
+otool -l $t/exe | grep -A9 'segname __FOO' | grep 'flags 0x4'

tests/allowable-client.sh

@@ -14,6 +14,8 @@ EOF
 $CC --ld-path=$mold -shared -o $t/libsub.dylib $t/a.o \
   -Wl,-umbrella,Big -Wl,-allowable_client,friend
 otool -l $t/libsub.dylib | grep 'client friend'
+# The umbrella commands follow the libraries, clients first (ld-prime).
+[ "$(otool -l $t/libsub.dylib | grep '^ *cmd ' | awk '{print $2}' | grep -E 'LC_LOAD_DYLIB|LC_SUB' | uniq | tr '\n' ' ')" = "LC_LOAD_DYLIB LC_SUB_CLIENT LC_SUB_FRAMEWORK " ]
 
 # A random client is rejected.
 not $CC --ld-path=$mold -o $t/exe $t/b.o $t/libsub.dylib 2> $t/log

tests/start-stop-symbol.sh

@@ -24,3 +24,8 @@ EOF
 
 $CC --ld-path=$mold -o $t/exe $t/a.o
 $t/exe > /dev/null
+# A __FOO segment conjured by a section$start boundary symbol is not an
+# -add_empty_section anchor: its segment carries no SG_NORELOC (0x0),
+# as ld-prime writes it.
+otool -l $t/exe > $t/lc
+[ "$(awk '/segname __FOO/{g=1} g&&/^ *flags/{print $2; exit}' $t/lc)" = 0x0 ]