binutils/add-ulp-section.diff

This is for userspace live patching, adding some space into
shared libs or executable (in the .ulp section) when one of the 
input files contains a section named .ulp.track.

Index: bfd/elflink.c
===================================================================
--- bfd/elflink.c.orig	2019-09-09 15:19:43.000000000 +0200
+++ bfd/elflink.c	2019-11-18 18:02:54.000000000 +0100
@@ -22,6 +22,7 @@
 #include "bfd.h"
 #include "bfdlink.h"
 #include "libbfd.h"
+#include "ulp.h"
 #define ARCH_SIZE 0
 #include "elf-bfd.h"
 #include "safe-ctype.h"
@@ -7070,6 +7071,11 @@ bfd_elf_size_dynamic_sections (bfd *outp
 	  s = bfd_get_linker_section (dynobj, ".gnu.version");
 	  s->flags |= SEC_EXCLUDE;
 	}
+
+      if (bfd_is_ulp_enabled(output_bfd))
+        {
+          bfd_setup_ulp(info);
+        }
     }
   return TRUE;
 }
Index: bfd/elfxx-x86.c
===================================================================
--- bfd/elfxx-x86.c.orig	2019-09-09 15:19:43.000000000 +0200
+++ bfd/elfxx-x86.c	2019-11-18 18:02:54.000000000 +0100
@@ -23,6 +23,7 @@
 #include "objalloc.h"
 #include "elf/i386.h"
 #include "elf/x86-64.h"
+#include "ulp.h"
 
 /* The name of the dynamic interpreter.  This is put in the .interp
    section.  */
@@ -952,6 +953,64 @@ _bfd_x86_elf_link_check_relocs (bfd *abf
   return _bfd_elf_link_check_relocs (abfd, info);
 }
 
+/* Check if input bfds are ulp-enabled by containing .ulp.track section */
+
+bfd_boolean
+bfd_x86_elf_is_ulp_enabled (struct bfd *input_bfd)
+{
+  while (input_bfd != NULL)
+  for (; input_bfd != NULL; input_bfd = input_bfd->link.next)
+    {
+      if (input_bfd->section_count == 0) continue;
+      if (bfd_get_section_by_name (input_bfd, ".ulp.track")) return TRUE;
+    }
+  return FALSE;
+}
+
+/* To be used by elf_link_hash_traverse when computing the ulp length */
+
+static bfd_boolean
+bfd_x86_elf_link_compute_ulp (struct elf_link_hash_entry *h, void *data)
+{
+  unsigned long *ulp_length = (unsigned long *) data;
+
+  if (h->dynindx != -1 && h->type == STT_FUNC && !h->def_dynamic)
+    {
+      ++(*ulp_length);
+    }
+  return TRUE;
+}
+
+/* Fill the user-space live patching section */
+
+bfd_boolean
+bfd_x86_elf_setup_ulp (struct bfd_link_info *info)
+{
+  struct elf_x86_link_hash_table *htab;
+  asection *ulp;
+  unsigned int ulp_length = 0;
+
+  htab = elf_x86_hash_table (info, X86_64_ELF_DATA);
+
+  elf_link_hash_traverse (elf_hash_table (info),
+                          bfd_x86_elf_link_compute_ulp,
+                          &ulp_length);
+
+  ulp = htab->ulp;
+
+  ulp->size = ulp_length * ULP_ENTRY_LEN;
+
+  ulp->contents = (bfd_byte *) bfd_malloc (ulp->size);
+  if (ulp->contents == NULL)
+    return FALSE;
+
+  if (!ulp->contents)
+    return FALSE;
+
+  memset(ulp->contents, 0x00, ulp->size);
+  return TRUE;
+}
+
 /* Set the sizes of the dynamic sections.  */
 
 bfd_boolean
@@ -2935,7 +2994,26 @@ error_alignment:
 
 	      htab->plt_second = sec;
 	    }
-	}
+
+         /* create sections to support user-space live patching */
+         if (bfd_x86_elf_is_ulp_enabled(info->input_bfds))
+           {
+             flagword flags = (bed->dynamic_sec_flags
+                               | SEC_ALLOC
+                               | SEC_CODE
+                               | SEC_LOAD
+                               | SEC_READONLY);
+
+              sec = bfd_make_section_anyway_with_flags (dynobj, ".ulp", flags);
+              if (sec == NULL)
+                info->callbacks->einfo (_("%F%P: failed to create ULP section\n"));
+
+              if (!bfd_set_section_alignment (dynobj, sec,  plt_alignment))
+                goto error_alignment;
+
+              htab->ulp = sec;
+           }
+      }
 
       if (!info->no_ld_generated_unwind_info)
 	{
Index: bfd/elfxx-x86.h
===================================================================
--- bfd/elfxx-x86.h.orig	2019-09-09 15:19:43.000000000 +0200
+++ bfd/elfxx-x86.h	2019-11-18 18:02:54.000000000 +0100
@@ -447,6 +447,7 @@ struct elf_x86_link_hash_table
   asection *plt_second_eh_frame;
   asection *plt_got;
   asection *plt_got_eh_frame;
+  asection *ulp;
 
   /* Parameters describing PLT generation, lazy or non-lazy.  */
   struct elf_x86_plt_layout plt;
Index: bfd/ulp.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ bfd/ulp.h	2019-11-18 18:02:54.000000000 +0100
@@ -0,0 +1,12 @@
+extern bfd_boolean bfd_x86_elf_is_ulp_enabled
+  (struct bfd *);
+
+extern bfd_boolean bfd_x86_elf_setup_ulp
+  (struct bfd_link_info *);
+
+#define bfd_is_ulp_enabled bfd_x86_elf_is_ulp_enabled
+
+#define bfd_setup_ulp bfd_x86_elf_setup_ulp
+
+#define ULP_ENTRY_LEN 16
+