[yocto] [prelink-cross][PATCH] Support copy relocations in .data.rel.ro

[Kyle Russell]

binutils-2.28 (17026142ef35b62ac88bfe517b4160614902cb28) adds support
for copying read-only dynamic symbols into .data.rel.ro instead of .bss
since .bss is technically writable.  This causes prelink to error out on
any binary containing COPY relocations in .data.rel.ro.

Read-only variables defined in shared libraries should be copied directly
into the space allocated for them in .data.rel.ro by the linker.

To achieve this, we determine whether either of the two sections
containing copy relocations is .data.rel.ro.  If so, we relocate the
symbol memory directly into the existing section instead of constructing
a new .(s)dynbss section once prelink_build_conflicts() returns.

Fixes cxx1.sh, cxx2.sh, and cxx3.sh on Fedora 28 (which uses
binutils-2.29).
---
 src/conflict.c | 51 +++++++++++++++++++++++++++++++++++++-------------
 src/undo.c     |  9 +++++++++
 2 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/src/conflict.c b/src/conflict.c
index 9ae2ddb..5613ace 100644
--- a/src/conflict.c
+++ b/src/conflict.c
@@ -450,7 +450,7 @@ get_relocated_mem (struct prelink_info *info, DSO *dso, GElf_Addr addr,
 int
 prelink_build_conflicts (struct prelink_info *info)
 {
-  int i, ndeps = info->ent->ndepends + 1;
+  int i, reset_dynbss = 0, reset_sdynbss = 0, ndeps = info->ent->ndepends + 1;
   struct prelink_entry *ent;
   int ret = 0;
   DSO *dso;
@@ -675,6 +675,11 @@ prelink_build_conflicts (struct prelink_info *info)
 		     dso->filename);
 	      goto error_out;
 	    }
+
+	  name = strptr (dso, dso->ehdr.e_shstrndx, dso->shdr[bss1].sh_name);
+	  if (strcmp(name, ".data.rel.ro") == 0)
+	    reset_sdynbss = 1;
+
 	  firstbss2 = i;
 	  info->sdynbss_size = cr.rela[i - 1].r_offset - cr.rela[0].r_offset;
 	  info->sdynbss_size += cr.rela[i - 1].r_addend;
@@ -702,6 +707,10 @@ prelink_build_conflicts (struct prelink_info *info)
 	    }
 	}
 
+      name = strptr (dso, dso->ehdr.e_shstrndx, dso->shdr[bss2].sh_name);
+      if (strcmp(name, ".data.rel.ro") == 0)
+        reset_dynbss = 1;
+
       info->dynbss_size = cr.rela[cr.count - 1].r_offset
 			  - cr.rela[firstbss2].r_offset;
       info->dynbss_size += cr.rela[cr.count - 1].r_addend;
@@ -719,9 +728,9 @@ prelink_build_conflicts (struct prelink_info *info)
 	  && strcmp (name = strptr (dso, dso->ehdr.e_shstrndx,
 				    dso->shdr[bss1].sh_name),
 		     ".dynbss") != 0
-	  && strcmp (name, ".sdynbss") != 0)
+	  && strcmp (name, ".sdynbss") != 0 && strcmp (name, ".data.rel.ro") != 0)
 	{
-	  error (0, 0, "%s: COPY relocations don't point into .bss or .sbss section",
+	  error (0, 0, "%s: COPY relocations don't point into .bss, .sbss, or .data.rel.ro sections",
 		 dso->filename);
 	  goto error_out;
 	}
@@ -730,9 +739,9 @@ prelink_build_conflicts (struct prelink_info *info)
 	  && strcmp (name = strptr (dso, dso->ehdr.e_shstrndx,
 				    dso->shdr[bss2].sh_name),
 		     ".dynbss") != 0
-	  && strcmp (name, ".sdynbss") != 0)
+	  && strcmp (name, ".sdynbss") != 0 && strcmp (name, ".data.rel.ro") != 0)
 	{
-	  error (0, 0, "%s: COPY relocations don't point into .bss or .sbss section",
+	  error (0, 0, "%s: COPY relocations don't point into .bss, .sbss, or .data.rel.ro section",
 		 dso->filename);
 	  goto error_out;
 	}
@@ -768,16 +777,21 @@ prelink_build_conflicts (struct prelink_info *info)
 	      }
 
 	  assert (j < ndeps);
+	  GElf_Addr symaddr = s->u.ent->base + s->value;
+	  char *buf;
+
 	  if (i < firstbss2)
-	    j = get_relocated_mem (info, ndso, s->u.ent->base + s->value,
-				   info->sdynbss + cr.rela[i].r_offset
-				   - info->sdynbss_base, cr.rela[i].r_addend,
-				   cr.rela[i].r_offset);
+	    if (reset_sdynbss)
+	      buf = get_data(dso, cr.rela[i].r_offset, NULL, NULL);
+	    else
+	      buf = info->sdynbss + cr.rela[i].r_offset - info->sdynbss_base;
 	  else
-	    j = get_relocated_mem (info, ndso, s->u.ent->base + s->value,
-				   info->dynbss + cr.rela[i].r_offset
-				   - info->dynbss_base, cr.rela[i].r_addend,
-				   cr.rela[i].r_offset);
+	    if (reset_dynbss)
+	      buf = get_data(dso, cr.rela[i].r_offset, NULL, NULL);
+	    else
+	      buf = info->dynbss + cr.rela[i].r_offset - info->dynbss_base;
+
+	  j = get_relocated_mem (info, ndso, symaddr, buf, cr.rela[i].r_addend, cr.rela[i].r_offset);
 
 	  switch (j)
 	    {
@@ -815,6 +829,17 @@ prelink_build_conflicts (struct prelink_info *info)
     if (info->dsos[i])
       close_dso (info->dsos[i]);
 
+  if (reset_sdynbss)
+    {
+      free (info->sdynbss);
+      info->sdynbss = NULL;
+    }
+
+  if (reset_dynbss)
+    {
+      free (info->dynbss);
+      info->dynbss = NULL;
+    }
   info->dsos = NULL;
   free (cr.rela);
   return ret;
diff --git a/src/undo.c b/src/undo.c
index 8a55bf2..4c38dab 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -633,6 +633,15 @@ prelink_undo (DSO *dso)
 	      d->d_buf = NULL;
 	      dso->shdr[i].sh_type = SHT_NOBITS;
 	    }
+	  else if (dso->shdr[i].sh_type == SHT_PROGBITS
+		   && strcmp (name, ".data.rel.ro") == 0)
+	    {
+	      scn = dso->scn[i];
+	      d = elf_getdata (scn, NULL);
+	      assert (d != NULL && elf_getdata (scn, d) == NULL);
+	      assert (d->d_size == dso->shdr[i].sh_size);
+	      assert (memset(d->d_buf, 0, d->d_size) == d->d_buf);
+	    }
 	  else if (dso->shdr[i].sh_type == SHT_RELA
 		   && shdr[i].sh_type == SHT_REL)
 	    {
-- 
2.17.1