From 03e0cef726571fa0f6435ae0ef9d4146a285b1f8 Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@cs.stanford.edu>
Date: Sat, 5 Feb 2022 11:57:36 +0900
Subject: [PATCH] [ELF] Add --warn-shared-textrel

---
 elf/cmdline.cc                  |  3 +++
 elf/input-sections.cc           | 12 +++++++++--
 elf/mold.h                      |  1 +
 elf/passes.cc                   |  3 +++
 test/elf/warn-shared-textrel.sh | 36 +++++++++++++++++++++++++++++++++
 5 files changed, 53 insertions(+), 2 deletions(-)
 create mode 100755 test/elf/warn-shared-textrel.sh

diff --git a/elf/cmdline.cc b/elf/cmdline.cc
index 74c17cbb..2f1e5b86 100644
--- a/elf/cmdline.cc
+++ b/elf/cmdline.cc
@@ -133,6 +133,7 @@ Options:
   --warn-common               Warn about common symbols
     --no-warn-common
   --warn-once                 Only warn once for each undefined symbol
+  --warn-shared-textrel       Warn if the output .so needs text relocations
   --warn-unresolved-symbols   Report unresolved symbols as warnings
     --error-unresolved-symbols
                               Report unresolved symbols as errors (default)
@@ -587,6 +588,8 @@ void parse_nonpositional_args(Context<E> &ctx,
       ctx.arg.warn_common = false;
     } else if (read_flag(args, "warn-once")) {
       ctx.arg.warn_once = true;
+    } else if (read_flag(args, "warn-shared-textrel")) {
+      ctx.arg.warn_shared_textrel = true;
     } else if (read_arg(ctx, args, arg, "compress-debug-sections")) {
       if (arg == "zlib" || arg == "zlib-gabi")
         ctx.arg.compress_debug_sections = COMPRESS_GABI;
diff --git a/elf/input-sections.cc b/elf/input-sections.cc
index 0a955f42..14c357b4 100644
--- a/elf/input-sections.cc
+++ b/elf/input-sections.cc
@@ -121,6 +121,12 @@ void InputSection<E>::dispatch(Context<E> &ctx, Action table[3][4], i64 i,
                << sym << "' can not be used; recompile with -fPIC";
   };
 
+  auto warn_textrel = [&]() {
+    if (ctx.arg.shared && ctx.arg.warn_shared_textrel)
+      Warn(ctx) << *this << ": relocation against symbol `" << sym
+                << "' in read-only section";
+  };
+
   switch (action) {
   case NONE:
     return;
@@ -148,10 +154,11 @@ void InputSection<E>::dispatch(Context<E> &ctx, Action table[3][4], i64 i,
     return;
   case DYNREL:
     if (!is_writable) {
-      if (!is_code || ctx.arg.z_text) {
+      if (ctx.arg.z_text) {
         error();
         return;
       }
+      warn_textrel();
       ctx.has_textrel = true;
     }
 
@@ -161,10 +168,11 @@ void InputSection<E>::dispatch(Context<E> &ctx, Action table[3][4], i64 i,
     return;
   case BASEREL:
     if (!is_writable) {
-      if (!is_code || ctx.arg.z_text) {
+      if (ctx.arg.z_text) {
         error();
         return;
       }
+      warn_textrel();
       ctx.has_textrel = true;
     }
 
diff --git a/elf/mold.h b/elf/mold.h
index 953ccddf..cf7b6562 100644
--- a/elf/mold.h
+++ b/elf/mold.h
@@ -1435,6 +1435,7 @@ struct Context {
     bool trace = false;
     bool warn_common = false;
     bool warn_once = false;
+    bool warn_shared_textrel = false;
     bool z_copyreloc = true;
     bool z_defs = false;
     bool z_delete = true;
diff --git a/elf/passes.cc b/elf/passes.cc
index dad03415..8278d84e 100644
--- a/elf/passes.cc
+++ b/elf/passes.cc
@@ -678,6 +678,9 @@ void scan_rels(Context<E> &ctx) {
 
   if (ctx.needs_tlsld)
     ctx.got->add_tlsld(ctx);
+
+  if (ctx.arg.shared && ctx.arg.warn_shared_textrel && ctx.has_textrel)
+    Warn(ctx) << "--warn-shared-textrel: creating a DT_TEXTREL in a shared object";
 }
 
 template <typename E>
diff --git a/test/elf/warn-shared-textrel.sh b/test/elf/warn-shared-textrel.sh
new file mode 100755
index 00000000..64cee4ca
--- /dev/null
+++ b/test/elf/warn-shared-textrel.sh
@@ -0,0 +1,36 @@
+#!/bin/bash
+export LANG=
+set -e
+CC="${CC:-cc}"
+CXX="${CXX:-c++}"
+testname=$(basename "$0" .sh)
+echo -n "Testing $testname ... "
+cd "$(dirname "$0")"/../..
+mold="$(pwd)/mold"
+t=out/test/elf/$testname
+mkdir -p $t
+
+# Skip if libc is musl
+echo 'int main() {}' | $CC -o $t/exe -xc -
+ldd $t/exe | grep -q ld-musl && { echo OK; exit; }
+
+# Skip if target is not x86-64
+[ "$(uname -m)" = x86_64 ] || { echo skipped; exit; }
+
+cat <<'EOF' | $CC -c -o $t/a.o -x assembler -
+.globl fn
+fn:
+  movabs main, %rax
+  ret
+EOF
+
+cat <<EOF | $CC -c -o $t/b.o -fPIC -xc -
+void fn();
+int main() { fn(); }
+EOF
+
+$CC -B. -shared -o $t/c.so $t/a.o $t/b.o -Wl,-warn-shared-textrel >& $t/log
+grep -q 'relocation against symbol `main'\'' in read-only section' $t/log
+grep -q 'creating a DT_TEXTREL in a shared object' $t/log
+
+echo OK