Re: [PATCH] Put absolute address jump table in data.rel.ro.local if targets support relocations

[HAO CHEN GUI via Gcc-patches]

Hi，

I just tweaked the patch according to your advice and committed it. 
Thanks so much for your help and advice.

Haochen Gui

On 13/11/2020 下午 5:27, Richard Sandiford wrote:
Hi,

Sorry for the slow reply.  Just one minor nit:

HAO CHEN GUI <guih...@linux.ibm.com> writes:
diff --git a/gcc/varasm.c b/gcc/varasm.c
index ea0b59cf44a..40502049b61 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -727,12 +727,26 @@ switch_to_other_text_partition (void)
    switch_to_section (current_function_section ());
  }
  
-/* Return the read-only data section associated with function DECL.  */
+/* Return the read-only or relocated read-only data section
+   associated with function DECL.  */
  
  section *
-default_function_rodata_section (tree decl)
+default_function_rodata_section (tree decl, bool relocatable)
  {
-  if (decl != NULL_TREE && DECL_SECTION_NAME (decl))
+  const char* sname;
+  unsigned int flags;
+
+  flags = 0;
+
+  if (relocatable)
+    {
+      sname = ".data.rel.ro.local";
+      flags = (SECTION_WRITE | SECTION_RELRO);
+    }
+  else
+    sname = ".rodata";
+
+  if (decl && DECL_SECTION_NAME (decl))
      {
        const char *name = DECL_SECTION_NAME (decl);
  
@@ -745,38 +759,57 @@ default_function_rodata_section (tree decl)
          dot = strchr (name + 1, '.');
          if (!dot)
            dot = name;
-         len = strlen (dot) + 8;
+         len = strlen (dot) + strlen (sname) + 1;
          rname = (char *) alloca (len);
  
-	  strcpy (rname, ".rodata");
+         strcpy (rname, sname);
          strcat (rname, dot);
-         return get_section (rname, SECTION_LINKONCE, decl);
+         return get_section (rname, (SECTION_LINKONCE | flags), decl);
        }
-      /* For .gnu.linkonce.t.foo we want to use .gnu.linkonce.r.foo.  */
+      /* For .gnu.linkonce.t.foo we want to use .gnu.linkonce.r.foo or
+        .gnu.linkonce.d.rel.ro.local.foo if the jump table is relocatable.  */
        else if (DECL_COMDAT_GROUP (decl)
               && strncmp (name, ".gnu.linkonce.t.", 16) == 0)
        {
-         size_t len = strlen (name) + 1;
-         char *rname = (char *) alloca (len);
+         size_t len;
+         char *rname;
  
-	  memcpy (rname, name, len);
-         rname[14] = 'r';
-         return get_section (rname, SECTION_LINKONCE, decl);
+         if (relocatable)
+           {
+             len = strlen (name) + strlen (".rel.ro.local") + 1;
+             rname = (char *) alloca (len);
+
+             strcpy (rname, ".gnu.linkonce.d");
+             strcat (rname, ".rel.ro.local");
+             strcat (rname, name + 15);
I realise you probably wrote it like this to make the correlation
between the length calculation and the string operations more
obvious, but IMO it would be less surprising to have:

              strcpy (rname, ".gnu.linkonce.d.rel.ro.local");

OK with that change, thanks.

Richard