Copy RELRO symbols to .copyrel.rel.ro instead of to .copyrel

So that readonly data wouldn't become writable by copy relocations.

elf/input-files.cc

@@ -1538,7 +1538,8 @@ bool SharedFile<E>::is_readonly(Symbol<E> *sym) {
   u64 val = sym->esym().st_value;
 
   for (ElfPhdr<E> &phdr : this->get_phdrs())
-    if (phdr.p_type == PT_LOAD && !(phdr.p_flags & PF_W) &&
+    if ((phdr.p_type == PT_LOAD || phdr.p_type == PT_GNU_RELRO) &&
+        !(phdr.p_flags & PF_W) &&
         phdr.p_vaddr <= val && val < phdr.p_vaddr + phdr.p_memsz)
       return true;
   return false;

test/elf/copyrel-relro2.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+cat <<EOF | $CC -o $t/a.o -c -xc -fno-PIE -
+#include <setjmp.h>
+#include <signal.h>
+#include <stdio.h>
+
+extern char readonly[100];
+extern char readwrite[100];
+
+static int segv = 0;
+static jmp_buf buf;
+
+void handler(int sig) {
+  segv = 1;
+  longjmp(buf, 1);
+}
+
+int main() {
+  signal(SIGSEGV, handler);
+
+  readwrite[0] = 5;
+  int x = segv;
+
+  if (setjmp(buf) == 0)
+    *(char *)readonly = 5;
+  int y = segv;
+
+  printf("sigsegv %d %d\n", x, y);
+}
+EOF
+
+cat <<EOF | $CC -fPIC -shared -o $t/b.so -xc -
+__attribute__((section (".data.rel.ro"))) char readonly[100] = "abc";
+char readwrite[100] = "abc";
+EOF
+
+$CC -B. $t/a.o $t/b.so -o $t/exe -no-pie
+$QEMU $t/exe | grep -q '^sigsegv 0 1$'