From mboxrd@z Thu Jan  1 00:00:00 1970
From: Scott Bambrough <scottb@netwinder.org>
To: libc-hacker mailing list <libc-hacker@sourceware.cygnus.com>
Subject: Patch to allow ARM dynamic linker to fix up PC24 relocs...
Date: Tue, 07 Dec 1999 11:50:00 -0000
Message-id: <384D63FD.D0F942FC@netwinder.org>
X-SW-Source: 1999-12/msg00011.html

Hi guys,

The attached patch allows the ARM dynamic linker to fix up PC24 relocs
in the code segment.  A bit of background is attached.

The PC24 reloc is generated for ARM branch and branch and link
instructions (b,bl).  The least significant 24 bits are used to for a 26
bit offset (the offset is modulo 4).  The address calculation performed
by the CPU is as follows:

PC = PC + (SignExtend(<24_bit_signed_offset>) << 2;

If the calculated 26 bit offset is out of range, the dynamic linker
displays an error message like the following:

foo_dynamic: error in loading shared libraries: ./foo.so: R_ARM_PC24
relocation out of range

1999-12-07  Scott Bambrough <scottb@netwinder.org>

	* sysdeps/arm/dl-machine.h (elf_machine_rel): Fixup R_ARM_PC24
 	  relocs if possible.

-- 
Scott Bambrough - Software Engineer
REBEL.COM    http://www.rebel.com
NetWinder    http://www.netwinder.org
--- dl-machine.h.orig	Fri Nov 26 08:56:05 1999
+++ dl-machine.h	Tue Dec  7 14:04:13 1999
@@ -446,6 +446,23 @@ elf_machine_rel (struct link_map *map, c
 	    *reloc_addr += value;
 	    break;
 	  }
+	case R_ARM_PC24:
+	  {
+	     signed int addend;
+
+	     addend = *reloc_addr & 0x00ffffff;
+	     if (addend & 0x00800000) addend |= 0xff000000;
+
+	     value = value - (unsigned int)reloc_addr + (addend << 2);
+	     if (value & 0xfc000003)
+	       _dl_signal_error (0, map->l_name,
+			  "R_ARM_PC24 relocation out of range");
+	       
+	     value = value >> 2;
+	     value = (*reloc_addr & 0xff000000) | (value & 0x00ffffff);
+	     *reloc_addr = value;
+	  }
+	break;
 	default:
 	  assert (! "unexpected dynamic reloc type");
 	  break;