+
−# The present patch to the ARM ELF linking code in binutils (made against
+
−# binutils-2.21.1a) is a hack that affects the generation of Thumb->ARM
+
−# call veneers.  The binutils linker can make these veneers in two forms:
+
−#
+
−#	"Short"			"Long"
+
−#	(16-bit) bx pc		(16-bit) bx pc
+
−#	(16-bit) nop		(16-bit) nop
+
−#	(32-bit) b dest		(32-bit) ldr pc, [pc, #-4]
+
−#				(32-bit) .long target
+
−#
+
−# For code that's going to run on the Calypso ARM7 processor, the
+
−# "short" form is the one we want: because of the way the address space
+
−# is laid out, the range of an ARM branch instruction will always be
+
−# sufficient for us, whereas the long version is more costly in terms
+
−# of the number of cycles required, especially when executing from
+
−# external memory.
+
−#
+
−# Unfortunately, the code which decides between these two forms
+
−# (located in the arm_type_of_stub() function in bfd/elf32-arm.c)
+
−# is broken.  The original code (which you can see below in the
+
−# "before" part of the patch hunk) exhibits two problems:
+
−#
+
−# 1. The distance that matters here is not from the original
+
−#    call point to the destination, but from the stub to
+
−#    the destination - and in this function we don't know
+
−#    where the stub will end up.
+
−#
+
−# 2. Because it's an ARM branch, the limits should be
+
−#    ARM_MAX_[BF]WD_BRANCH_OFFSET, not the THM_ ones.
+
−#
+
−# The 2nd problem would be trivial to fix, but the 1st one
+
−# much less so: this function doesn't know where the stub
+
−# will end up, and considering that for the present purpose
+
−# of the FreeCalypso project always emitting the "short"
+
−# version would be perfect, there is no justification for
+
−# expending the time and effort to restructure the linker
+
−# to do the proper relaxation for the case at hand.
+
−#
+
−# Therefore, the patch we apply is a hack: we simply force the
+
−# use of the "short" form unconditionally.
+
−
+
−*** elf32-arm.c	Wed May 11 07:29:12 2011
+
−--- elf32-arm-patched.c	Mon Aug 19 03:24:38 2013
+
−***************
+
−*** 3203,3211 ****
+
−  		   : arm_stub_long_branch_v4t_thumb_arm);
+
−  
+
−  	      /* Handle v4t short branches.  */
+
−! 	      if ((stub_type == arm_stub_long_branch_v4t_thumb_arm)
+
−! 		  && (branch_offset <= THM_MAX_FWD_BRANCH_OFFSET)
+
−! 		  && (branch_offset >= THM_MAX_BWD_BRANCH_OFFSET))
+
−  		stub_type = arm_stub_short_branch_v4t_thumb_arm;
+
−  	    }
+
−  	}
+
−--- 3203,3209 ----
+
−  		   : arm_stub_long_branch_v4t_thumb_arm);
+
−  
+
−  	      /* Handle v4t short branches.  */
+
−! 	      if (stub_type == arm_stub_long_branch_v4t_thumb_arm)
+
−  		stub_type = arm_stub_short_branch_v4t_thumb_arm;
+
−  	    }
+
−  	}