Commit b23404af3d3141037f83257379743c9cdb0de473 | zig

author	Jacob Young <jacobly@ziglang.org> 2026-06-12 07:29:14-04:00
committer	Andrew Kelley <andrew@ziglang.org> 2026-06-16 22:48:18+02:00
log	b23404af3d3141037f83257379743c9cdb0de473
tree	95f1675b826838265ea8ab72167eb449720e569c
parent	b64ce08c993f0871b2f9be7df561da69d9a9037e

DynLib: fix elf loading

The comment was just bogus given that these are private (COW) mappings.
This code will need extra logic for handling multiple load segments
overlapping the same page, but the deleted logic was not even close.

Closes #30966

5 files changed, 28 insertions(+), 30 deletions(-)

lib
- std
  - dynamic_library.zig
test
- standalone
  - load_dynamic_library
    add.zig
    build.zig
    lib.zig
    main.zig

lib/std/dynamic_library.zig+8-21

 @@ -302,27 +302,14 @@ pub const ElfDynLib = struct {
                         const extended_memsz = mem.alignForward(usize, ph.p_memsz + extra_bytes, page_size);
                         const ptr = @as([*]align(std.heap.page_size_min) u8, @ptrFromInt(aligned_addr));
                         const prot = elfToProt(ph.p_flags);
-                        if ((ph.p_flags & elf.PF_W) == 0) {
+                        _ = try posix.mmap(
-                            // If it does not need write access, it can be mapped from the fd.
+                            ptr,
-                            _ = try posix.mmap(
+                            extended_memsz,
-                                ptr,
+                            prot,
-                                extended_memsz,
+                            .{ .TYPE = .PRIVATE, .FIXED = true },
-                                prot,
+                            file.handle,
-                                .{ .TYPE = .PRIVATE, .FIXED = true },
+                            ph.p_offset - extra_bytes,
-                                file.handle,
+                        );
-                                ph.p_offset - extra_bytes,
-                            );
-                        } else {
-                            const sect_mem = try posix.mmap(
-                                ptr,
-                                extended_memsz,
-                                prot,
-                                .{ .TYPE = .PRIVATE, .FIXED = true, .ANONYMOUS = true },
-                                -1,
-                                0,
-                            );
-                            @memcpy(sect_mem[0..ph.p_filesz], file_bytes[0..ph.p_filesz]);
-                        }
                     },
                     else => {},
                 }

test/standalone/load_dynamic_library/add.zig deleted-3

...	@@ -1,3 +0,0 @@
1	export fn add(a: i32, b: i32) i32 {
2	return a + b;
3	}

test/standalone/load_dynamic_library/build.zig+6-2

 @@ -11,12 +11,16 @@ pub fn build(b: *std.Build) void {
     if (builtin.os.tag == .wasi) return;
     if (builtin.os.tag == .windows) return;
+    // ld and lld do not agree on the format of the .hash section
+    // Tracked by https://codeberg.org/ziglang/zig/issues/35746
+    if (builtin.cpu.arch == .s390x and builtin.os.tag == .linux) return;
     const lib = b.addLibrary(.{
         .linkage = .dynamic,
-        .name = "add",
+        .name = "lib",
         .version = .{ .major = 1, .minor = 0, .patch = 0 },
         .root_module = b.createModule(.{
-            .root_source_file = b.path("add.zig"),
+            .root_source_file = b.path("lib.zig"),
             .optimize = optimize,
             .target = target,
         }),

test/standalone/load_dynamic_library/lib.zig created+8

...	@@ -0,0 +1,8 @@
1	export fn addInts(a: i32, b: i32) i32 {
2	return a + b;
3	}
4
5	var forty_two: i32 = 42;
6	export fn fortyTwo() i32 {
7	return forty_two;
8	}

test/standalone/load_dynamic_library/main.zig+6-4

 @@ -8,9 +8,11 @@ pub fn main(init: std.process.Init) !void {
     var lib = try std.DynLib.open(dynlib_name);
     defer lib.close();
-    const Add = *const fn (i32, i32) callconv(.c) i32;
+    const AddInts = *const fn (i32, i32) callconv(.c) i32;
-    const addFn = lib.lookup(Add, "add") orelse return error.SymbolNotFound;
+    const addInts = lib.lookup(AddInts, "addInts").?;
+    std.debug.assert(addInts(12, 34) == 46);
-    const result = addFn(12, 34);
+    const FortyTwo = *const fn () callconv(.c) i32;
-    std.debug.assert(result == 46);
+    const fortyTwo = lib.lookup(FortyTwo, "fortyTwo").?;
+    std.debug.assert(fortyTwo() == 42);
 }