Alexandre Oliva writes:

This patch adds code to uClibc to support a new ABI designed for the
FR-V architecture, that enables text segments of executables and
shared libraries to be shared by multiple processes on an OS such as
uClinux, that can run on FR-V processors without an MMU.

Patches for binutils and GCC have just been posted in the
corresponding mailing lists.  The binutils patch was approved,
but there's one additional patch pending review, that I posted
this week.  An updated GCC patch will be posted to
gcc-patches@gcc.gnu.org as soon as I complete testing (I used a
known-good compiler to test the uClibc patch below).

Since the existing dynamic loader code didn't support independent
relocation of segments, it required changes that were somewhat
extensive.  I've added a number of new machine-specific macros to try
to keep the platform and ABI-specific details outside the generic
code.  I hope this is not a problem.

1 files changed, 104 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/frv/bits/elf-fdpic.h b/libc/sysdeps/linux/frv/bits/elf-fdpic.h
new file mode 100644
index 000000000..f47d9493c
--- /dev/null
+++ b/libc/sysdeps/linux/frv/bits/elf-fdpic.h
@@ -0,0 +1,104 @@
+/* Copyright 2003 Free Software Foundation, Inc.
+This file is part of the GNU C Library.
+
+The GNU C Library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public License as
+published by the Free Software Foundation; either version 2.1 of the
+License, or (at your option) any later version.
+
+The GNU C Library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Library General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA.  */
+
+#ifndef _BITS_ELF_FDPIC_H
+#define _BITS_ELF_FDPIC_H
+
+/* These data structures are described in the FDPIC ABI extension.
+   The kernel passes a process a memory map, such that for every LOAD
+   segment there is an elf32_fdpic_loadseg entry.  A pointer to an
+   elf32_fdpic_loadmap is passed in GR8 at start-up, and a pointer to
+   an additional such map is passed in GR9 for the interpreter, when
+   there is one.  */
+
+#include <elf.h>
+
+/* This data structure represents a PT_LOAD segment.  */
+struct elf32_fdpic_loadseg
+{
+  /* Core address to which the segment is mapped.  */
+  Elf32_Addr addr;
+  /* VMA recorded in the program header.  */
+  Elf32_Addr p_vaddr;
+  /* Size of this segment in memory.  */
+  Elf32_Word p_memsz;
+};
+
+struct elf32_fdpic_loadmap {
+  /* Protocol version number, must be zero.  */
+  Elf32_Half version;
+  /* Number of segments in this map.  */
+  Elf32_Half nsegs;
+  /* The actual memory map.  */
+  struct elf32_fdpic_loadseg segs[/*nsegs*/];
+};
+
+struct elf32_fdpic_loadaddr {
+  struct elf32_fdpic_loadmap *map;
+  void *got_value;
+};
+
+/* Map a pointer's VMA to its corresponding address according to the
+   load map.  */
+inline static void *
+__reloc_pointer (void *p,
+		 const struct elf32_fdpic_loadmap *map)
+{
+  int c;
+
+#if 0
+  if (map->version != 0)
+    /* Crash.  */
+    ((void(*)())0)();
+#endif
+
+  /* No special provision is made for NULL.  We don't want NULL
+     addresses to go through relocation, so they shouldn't be in
+     .rofixup sections, and, if they're present in dynamic
+     relocations, they shall be mapped to the NULL address without
+     undergoing relocations.  */
+
+  for (c = 0;
+       /* Take advantage of the fact that the loadmap is ordered by
+	  virtual addresses.  In general there will only be 2 entries,
+	  so it's not profitable to do a binary search.  */
+       c < map->nsegs && p >= (void*)map->segs[c].p_vaddr;
+       c++)
+    {
+      /* This should be computed as part of the pointer comparison
+	 above, but we want to use the carry in the comparison, so we
+	 can't convert it to an integer type beforehand.  */
+      unsigned long offset = p - (void*)map->segs[c].p_vaddr;
+      /* We explicitly refrain from checking for one-past-the-end.
+	 Zero-sized objects aren't legal, and it's expected that array
+	 addresses will be relocated before the addend that would make
+	 it one-past-the-end is added.  This gives us a reasonable speed
+	 up, and we couldn't possibly disambiguate all cases anyway.  */
+      if (offset < map->segs[c].p_memsz)
+	return (char*)map->segs[c].addr + offset;
+    }
+	     
+  /* We might want to crash instead.  */
+  return (void*)-1;
+}
+
+# define __RELOC_POINTER(ptr, loadaddr) \
+  (__reloc_pointer ((void*)(ptr), \
+		    (loadaddr).map))
+
+#endif /* _BITS_ELF_FDPIC_H */