ARM: Define custom ELF headers for ARM.

At least when building with the gnu toolchain, the headers the linker
automatically generate save space for the actual ELF headers in one of the
loadable segments. This creates two problems. First, the data you intended to
be at the start of the image doesn't actually show up there, it's actually the
ELF headers. Second, the ELF headers are essentially useless for firmware
since there's currently nothing to tell you where they are, and even if there
was, there isn't much of a reason to look at them. They're useful in userspace
for, for instance, the dynamic linker, but not really in firmware.

This change adds a PHDRS construct to each of the linker scripts used on ARM
which define a single segment called to_load which does not have the flag set
which would tell the linker to put headers in it. The first section defined in
the script has ": to_load" to tell the linker which segment to put it in, and
from that point on the other sections go in there by default.

BUG=None
TEST=Built and booted on nyan. Verified that the ROM stage was less than 18KB.
Reverted the change which forced ROM stage alignment and saw that the ROM
stage stayed the same size.
BRANCH=None

Change-Id: Ie2670f33f0421b16b2d4663fbfa99358890c77e4
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/180163
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Tom Warren <twarren@nvidia.com>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>

src/arch/arm/bootblock.ld

@@ -23,6 +23,11 @@ OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 OUTPUT_ARCH(arm)
 INCLUDE ldoptions
 
+PHDRS
+{
+	to_load PT_LOAD;
+}
+
 ENTRY(_start)
 TARGET(binary)
 SECTIONS
@@ -42,7 +47,7 @@ SECTIONS
 		*(.bss.*);
 		*(.sbss);
 		*(.sbss.*);
-	} = 0xff
+	} : to_load = 0xff
 
 	/DISCARD/ : {
 		*(.comment)

src/arch/arm/coreboot_ram.ld

@@ -22,6 +22,11 @@
 /* We use ELF as output format. So that we can debug the code in some form. */
 INCLUDE ldoptions
 
+PHDRS
+{
+	to_load PT_LOAD;
+}
+
 ENTRY(stage_entry)
 
 SECTIONS
@@ -38,7 +43,7 @@ SECTIONS
 		*(.text.*);
 		. = ALIGN(16);
 		_etext = .;
-	}
+	} : to_load
 
 	.ctors : {
 		. = ALIGN(0x100);

src/arch/arm/romstage.ld

@@ -29,6 +29,11 @@ OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 OUTPUT_ARCH(arm)
 INCLUDE ldoptions
 
+PHDRS
+{
+	to_load PT_LOAD;
+}
+
 ENTRY(stage_entry)
 
 SECTIONS
@@ -41,7 +46,7 @@ SECTIONS
 		*(.text.startup);
 		*(.text);
 		*(.text.*);
-	}
+	} : to_load
 
 	.romdata . : {
 		*(.rodata);