Commit 4e45362529e05ba1be44fab48bc3469f5bb6492d | zig

author	Matthew Lugg <mlugg@mlugg.co.uk> 2025-09-10 16:41:10+01:00
committer	Matthew Lugg <mlugg@mlugg.co.uk> 2025-09-30 13:44:53+01:00
log	4e45362529e05ba1be44fab48bc3469f5bb6492d
tree	b8d161294f8519ed8471b7cdb84ff2aa037e4368
parent	1123741fd5fc6545daf10e2bcdcad74ec148f61b
signature	Commit is signed but in an unrecognized format.

link.Elf: fix static PIE

We mustn't emit the DT_PLTGOT entry in `.dynamic` in a statically-linked
PIE, because there's no dl to relocate it (and `std.pie.relocate`, or
the PIE relocator in libc, won't touch it). In that case, there cannot
be any PLT entries, so there's no point emitting the `.got.plt` section
at all. If we just don't create that section, `link.Elf` already knows
not to add the DT_PLTGOT entry to `.dynamic`.

Co-authored-by: Jacob Young <jacobly0@users.noreply.github.com>

2 files changed, 23 insertions(+), 19 deletions(-)

lib
- std
  - dynamic_library.zig
src
- link
  - Elf.zig

lib/std/dynamic_library.zig+1-2

...	@@ -95,8 +95,7 @@ pub fn get_DYNAMIC() ?[*]const elf.Dyn {	...	@@ -95,8 +95,7 @@ pub fn get_DYNAMIC() ?[*]const elf.Dyn {
95	pub fn linkmap_iterator(phdrs: []const elf.Phdr) error{InvalidExe}!LinkMap.Iterator {	95	pub fn linkmap_iterator(phdrs: []const elf.Phdr) error{InvalidExe}!LinkMap.Iterator {
96	_ = phdrs;	96	_ = phdrs;
97	const _DYNAMIC = get_DYNAMIC() orelse {	97	const _DYNAMIC = get_DYNAMIC() orelse {
98	// No PT_DYNAMIC means this is either a statically-linked program or a	98	// No PT_DYNAMIC means this is a statically-linked non-PIE program.
99	// badly corrupted dynamically-linked one.
100	return .{ .current = null };	99	return .{ .current = null };
101	};	100	};
102		101

src/link/Elf.zig+22-17

 @@ -1884,6 +1884,16 @@ fn initSyntheticSections(self: *Elf) !void {
     const ptr_size = self.ptrWidthBytes();
     const shared_objects = self.shared_objects.values();
+    const is_exe_or_dyn_lib = switch (comp.config.output_mode) {
+        .Exe => true,
+        .Lib => comp.config.link_mode == .dynamic,
+        .Obj => false,
+    };
+    const have_dynamic_linker = comp.config.link_mode == .dynamic and is_exe_or_dyn_lib and !target.dynamic_linker.eql(.none);
+    const needs_interp = have_dynamic_linker and
+        (comp.config.link_libc or comp.root_mod.resolved_target.is_explicit_dynamic_linker);
     const needs_eh_frame = blk: {
         if (self.zigObjectPtr()) |zo|
             if (zo.eh_frame_index != null) break :blk true;
 @@ -1891,6 +1901,7 @@ fn initSyntheticSections(self: *Elf) !void {
             if (self.file(index).?.object.cies.items.len > 0) break true;
         } else false;
     };
     if (needs_eh_frame) {
         if (self.section_indexes.eh_frame == null) {
             self.section_indexes.eh_frame = self.sectionByName(".eh_frame") orelse try self.addSection(.{
 @@ -1922,13 +1933,17 @@ fn initSyntheticSections(self: *Elf) !void {
         });
     }
-    if (self.section_indexes.got_plt == null) {
+    if (have_dynamic_linker) {
-        self.section_indexes.got_plt = try self.addSection(.{
+        if (self.section_indexes.got_plt == null) {
-            .name = try self.insertShString(".got.plt"),
+            self.section_indexes.got_plt = try self.addSection(.{
-            .type = elf.SHT_PROGBITS,
+                .name = try self.insertShString(".got.plt"),
-            .flags = elf.SHF_ALLOC | elf.SHF_WRITE,
+                .type = elf.SHT_PROGBITS,
-            .addralign = @alignOf(u64),
+                .flags = elf.SHF_ALLOC | elf.SHF_WRITE,
-        });
+                .addralign = @alignOf(u64),
+            });
+        }
+    } else {
+        assert(self.plt.symbols.items.len == 0);
     }
     const needs_rela_dyn = blk: {
 @@ -1989,16 +2004,6 @@ fn initSyntheticSections(self: *Elf) !void {
         });
     }
-    const is_exe_or_dyn_lib = switch (comp.config.output_mode) {
-        .Exe => true,
-        .Lib => comp.config.link_mode == .dynamic,
-        .Obj => false,
-    };
-    const have_dynamic_linker = comp.config.link_mode == .dynamic and is_exe_or_dyn_lib and !target.dynamic_linker.eql(.none);
-    const needs_interp = have_dynamic_linker and
-        (comp.config.link_libc or comp.root_mod.resolved_target.is_explicit_dynamic_linker);
     if (needs_interp and self.section_indexes.interp == null) {
         self.section_indexes.interp = try self.addSection(.{
             .name = try self.insertShString(".interp"),