coreboot: x86: enable gc-sections

Garbage collected sections allow for trimming the size of the
binaries as well as allowing for not needing to config off
unused functions. To that end, on a rambi build the following
differences are observed:

$ diff -up \
	<(readelf -l coreboot-builds/google_rambi/cbfs/fallback/ramstage.elf) \
	<(readelf -l coreboot-builds/google_rambi_gc_sections/cbfs/fallback/ramstage.elf)
--- /dev/fd/63  2015-03-10 12:07:27.927985430 -0500
+++ /dev/fd/62  2015-03-10 12:07:27.927985430 -0500
@@ -6,9 +6,9 @@ There are 4 program headers, starting at
 Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg
Align
   LOAD           0x001000 0x00000000 0x00000000 0x00040 0x00040 RWE 0
-  LOAD           0x001040 0x00000040 0x00000040 0x34560 0x34560 RWE 0
-  LOAD           0x0355a0 0x000345a0 0x000345a0 0x02578 0x02578 RWE 0
-  LOAD           0x037b18 0x00036b18 0x00036b18 0x00000 0x0b560     0
+  LOAD           0x001040 0x00000040 0x00000040 0x2cbf8 0x2cbf8 RWE 0
+  LOAD           0x02dc38 0x0002cc38 0x0002cc38 0x02208 0x02208 RWE 0
+  LOAD           0x02fe40 0x0002ee40 0x0002ee40 0x00000 0x0a888     0

  Section to Segment mapping:
   Segment Sections...

$ diff -up \
	<(readelf -l coreboot-builds/google_rambi/cbfs/fallback/romstage.elf) \
	<(readelf -l coreboot-builds/google_rambi_gc_sections/cbfs/fallback/romstage.elf)
--- /dev/fd/63  2015-03-10 12:08:16.855985880 -0500
+++ /dev/fd/62  2015-03-10 12:08:16.851985880 -0500
@@ -5,8 +5,8 @@ There are 1 program headers, starting at

 Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg
Align
-  LOAD           0x000060 0xfff20000 0xfff20000 0x08b81 0x08b81 R E
   0x10
+  LOAD           0x000060 0xfff20000 0xfff20000 0x06300 0x06300 R E
0x10

  Section to Segment mapping:
   Segment Sections...
-   00     .rom .text
+   00     .rom

The following warnings needed to be applied to CFLAGS_common because for
some reason gcc was miraculously emitting the warnings with the
unrelated *-sections options:
  -Wno-unused-but-set-variable

Change-Id: I210784fdfc273ce4cb9927352cbd5a51be3c6929
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/8635
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

1 files changed, 7 insertions, 4 deletions

diff --git a/src/arch/x86/ramstage.ld b/src/arch/x86/ramstage.ld
index 1c8e8dcd6f..0843be7906 100644
--- a/src/arch/x86/ramstage.ld
+++ b/src/arch/x86/ramstage.ld
@@ -42,7 +42,7 @@ SECTIONS
 	.ctors : {
 		. = ALIGN(0x100);
 		__CTOR_LIST__ = .;
-		*(.ctors);
+		KEEP(*(.ctors));
 		LONG(0);
 		__CTOR_END__ = .;
 	}
@@ -55,13 +55,13 @@ SECTIONS
 		 * section names the equivalent changes need to made to
 		 * rmodule.ld. */
 		pci_drivers = . ;
-		*(.rodata.pci_driver)
+		KEEP(*(.rodata.pci_driver));
 		epci_drivers = . ;
 		cpu_drivers = . ;
-		*(.rodata.cpu_driver)
+		KEEP(*(.rodata.cpu_driver));
 		ecpu_drivers = . ;
 		_bs_init_begin = .;
-		*(.bs_init)
+		KEEP(*(.bs_init));
 		_bs_init_end = .;
 
 		*(.rodata)
@@ -82,6 +82,7 @@ SECTIONS
 	.data : {
 		_data = .;
 		*(.data)
+		*(.data.*)
 		_edata = .;
 	}
 
@@ -92,7 +93,9 @@ SECTIONS
 	_bss = .;
 	.bss . : {
 		*(.bss)
+		*(.bss.*)
 		*(.sbss)
+		*(.sbss.*)
 		*(COMMON)
 	}
 	_ebss = .;