From 8672fba5020ec72acf931a9a63b12a3c57f6c5cb Mon Sep 17 00:00:00 2001
From: Jakub Konka <kubkon@jakubkonka.com>
Date: Fri, 21 Jul 2023 23:25:01 +0200
Subject: [PATCH] elf: handle text relocations

---
 src/Elf.zig           |  1 +
 src/Elf/Atom.zig      |  6 +-----
 src/Elf/Options.zig   |  4 ++--
 src/Elf/synthetic.zig |  9 ++++++++
 test/elf.zig          | 48 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 61 insertions(+), 7 deletions(-)

diff --git a/src/Elf.zig b/src/Elf.zig
index 8681960f..1726c87f 100644
--- a/src/Elf.zig
+++ b/src/Elf.zig
@@ -87,6 +87,7 @@ comdat_groups_owners: std.ArrayListUnmanaged(ComdatGroupOwner) = .{},
 comdat_groups_table: std.AutoHashMapUnmanaged(u32, ComdatGroupOwner.Index) = .{},
 
 needs_tlsld: bool = false,
+has_text_reloc: bool = false,
 num_ifunc_dynrelocs: usize = 0,
 default_sym_version: elf.Elf64_Versym,
 
diff --git a/src/Elf/Atom.zig b/src/Elf/Atom.zig
index 5c78053e..1aecc1de 100644
--- a/src/Elf/Atom.zig
+++ b/src/Elf/Atom.zig
@@ -349,11 +349,7 @@ inline fn checkTextReloc(self: Atom, symbol: *const Symbol, elf_file: *Elf) void
                 symbol.getName(elf_file),
             });
         } else {
-            // TODO
-            elf_file.base.fatal("{s}: {s}: TODO handle relocations in read-only section", .{
-                self.getObject(elf_file).fmtPath(),
-                self.getName(elf_file),
-            });
+            elf_file.has_text_reloc = true;
         }
     }
 }
diff --git a/src/Elf/Options.zig b/src/Elf/Options.zig
index 2c3cb12e..cf8644b0 100644
--- a/src/Elf/Options.zig
+++ b/src/Elf/Options.zig
@@ -57,7 +57,7 @@ const usage =
     \\  nodlopen                    Mark DSO not available to dlopen
     \\  now                         Disable lazy function resolution
     \\  stack-size=[value]          Override default stack size
-    \\  text                        Do not allow relocations against read-only segments (default)
+    \\  text                        Do not allow relocations against read-only segments
     \\    notext                    
     \\  relro                       Make some sections read-only after dynamic relocations
     \\    norelro                   
@@ -115,7 +115,7 @@ z_nocopyreloc: bool = false,
 /// Mark DSO not available for dlopen.
 z_nodlopen: bool = false,
 /// Do not allow relocations against read-only segments.
-z_text: bool = true,
+z_text: bool = false,
 /// Make some sections read-only after dynamic relocations.
 /// TODO make this default to true.
 z_relro: bool = false,
diff --git a/src/Elf/synthetic.zig b/src/Elf/synthetic.zig
index dc9baa68..abf55855 100644
--- a/src/Elf/synthetic.zig
+++ b/src/Elf/synthetic.zig
@@ -42,6 +42,9 @@ pub const DynamicSection = struct {
             },
             else => {},
         };
+        if (elf_file.has_text_reloc) {
+            flags |= elf.DF_TEXTREL;
+        }
         return if (flags > 0) flags else null;
     }
 
@@ -75,6 +78,7 @@ pub const DynamicSection = struct {
         if (elf_file.got_plt_sect_index != null) nentries += 1; // PLTGOT
         nentries += 1; // HASH
         if (elf_file.gnu_hash_sect_index != null) nentries += 1; // GNU_HASH
+        if (elf_file.has_text_reloc) nentries += 1; // TEXTREL
         nentries += 1; // SYMTAB
         nentries += 1; // SYMENT
         nentries += 1; // STRTAB
@@ -165,6 +169,11 @@ pub const DynamicSection = struct {
             try writer.writeStruct(elf.Elf64_Dyn{ .d_tag = elf.DT_GNU_HASH, .d_val = addr });
         }
 
+        // TEXTREL
+        if (elf_file.has_text_reloc) {
+            try writer.writeStruct(elf.Elf64_Dyn{ .d_tag = elf.DT_TEXTREL, .d_val = 0 });
+        }
+
         // SYMTAB + SYMENT
         {
             assert(elf_file.dynsymtab_sect_index != null);
diff --git a/test/elf.zig b/test/elf.zig
index 9c44bcbd..d30707f9 100644
--- a/test/elf.zig
+++ b/test/elf.zig
@@ -69,6 +69,7 @@ pub fn addElfTests(b: *Build, opts: Options) *Step {
         elf_step.dependOn(testWeakExportExe(b, opts));
         elf_step.dependOn(testWeakUndefDso(b, opts));
         elf_step.dependOn(testZNow(b, opts));
+        elf_step.dependOn(testZText(b, opts));
     }
 
     return elf_step;
@@ -3007,6 +3008,53 @@ fn testZNow(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+fn testZText(b: *Build, opts: Options) *Step {
+    const test_step = b.step("test-elf-z-text", "");
+
+    const a_o = cc(b, opts);
+    a_o.addAsmSource(
+        \\.globl fn1
+        \\fn1:
+        \\  sub $8, %rsp
+        \\  movabs ptr, %rax
+        \\  call *%rax
+        \\  add $8, %rsp
+        \\  ret
+    );
+    a_o.addArg("-c");
+
+    const b_o = cc(b, opts);
+    b_o.addCSource(
+        \\#include <stdio.h>
+        \\int fn1();
+        \\int fn2() {
+        \\  return 3;
+        \\}
+        \\void *ptr = fn2;
+        \\int main() {
+        \\  printf("%d\n", fn1());
+        \\}
+    );
+    b_o.addArgs(&.{ "-fPIC", "-c" });
+
+    const exe = cc(b, opts);
+    exe.addFileSource(a_o.out);
+    exe.addFileSource(b_o.out);
+    exe.addArg("-pie");
+
+    const run = exe.run();
+    run.expectStdOutEqual("3\n");
+    test_step.dependOn(run.step());
+
+    const check = exe.check();
+    check.checkInDynamicSection();
+    // check.checkExact("TEXTREL 0"); // TODO fix in CheckObject parser
+    check.checkExact("FLAGS TEXTREL");
+    test_step.dependOn(&check.step);
+
+    return test_step;
+}
+
 fn cc(b: *Build, opts: Options) SysCmd {
     const cmd = Run.create(b, "cc");
     cmd.addArgs(&.{ "cc", "-fno-lto" });