[U-Boot] [RFC PATCH] ppc4xx: Use gc-sections to reduce image size

[Stefan Roese]

This patch enables gc-sections for PPC4xx. This is done to
generate smaller U-Boot images. For this the linker script
also needs some tweaking:

- For example change *(text) to *(text*)
- Add KEEP to some of the symbols, especially "resetvec"

This patch is tested on the following boards and reduces
the image size by the these values:

Canyonlands: 11,642
Katmai:       9,170
Kilauea:     10,742
Sequoia:     11,398

Additionally this patch integrates a bit of cleanup to the
PPC4xx default linker script.

Please note that this patch only enables gc-sections for PPC4xx.
Other PowerPC's may enable it as well but also need to change
the linker scripts accordingly. I didn't do this in this patch
since I can't test all those platforms/boards.

Once all PowerPC platforms have gc-sections enabled, the
changes to arch/powerpc/cpu/ppc4xx/config.mk should be moved
to arch/powerpc/config.mk

Signed-off-by: Stefan Roese <sr at denx.de>
---
 arch/powerpc/cpu/ppc4xx/config.mk  |    6 ++++
 arch/powerpc/cpu/ppc4xx/u-boot.lds |   53 +++++++-----------------------------
 2 files changed, 16 insertions(+), 43 deletions(-)

diff --git a/arch/powerpc/cpu/ppc4xx/config.mk b/arch/powerpc/cpu/ppc4xx/config.mk
index 5bda710..b0d346a 100644
--- a/arch/powerpc/cpu/ppc4xx/config.mk
+++ b/arch/powerpc/cpu/ppc4xx/config.mk
@@ -33,5 +33,11 @@ else
 PLATFORM_CPPFLAGS += -Wa,-m405 -mcpu=405
 endif
 
+# Enable gc-sections to enable generation of smaller images.
+# Please note that the linker scripts may need some tweaking with this
+# change as well.
+PLATFORM_LDFLAGS += --gc-sections
+PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections
+
 # Use default linker script.  Board port can override in board/*/config.mk
 LDSCRIPT := $(SRCTREE)/arch/powerpc/cpu/ppc4xx/u-boot.lds
diff --git a/arch/powerpc/cpu/ppc4xx/u-boot.lds b/arch/powerpc/cpu/ppc4xx/u-boot.lds
index eca1f9d..c3e0e16 100644
--- a/arch/powerpc/cpu/ppc4xx/u-boot.lds
+++ b/arch/powerpc/cpu/ppc4xx/u-boot.lds
@@ -27,8 +27,7 @@
 #endif
 
 OUTPUT_ARCH(powerpc)
-/* Do we need any of these for elf?
-   __DYNAMIC = 0;    */
+
 PHDRS
 {
   text PT_LOAD;
@@ -39,43 +38,16 @@ SECTIONS
 {
   /* Read-only sections, merged into text segment: */
   . = + SIZEOF_HEADERS;
-  .interp : { *(.interp) }
-  .hash          : { *(.hash)		}
-  .dynsym        : { *(.dynsym)		}
-  .dynstr        : { *(.dynstr)		}
-  .rel.text      : { *(.rel.text)		}
-  .rela.text     : { *(.rela.text)	}
-  .rel.data      : { *(.rel.data)		}
-  .rela.data     : { *(.rela.data)	}
-  .rel.rodata    : { *(.rel.rodata)	}
-  .rela.rodata   : { *(.rela.rodata)	}
-  .rel.got       : { *(.rel.got)		}
-  .rela.got      : { *(.rela.got)		}
-  .rel.ctors     : { *(.rel.ctors)	}
-  .rela.ctors    : { *(.rela.ctors)	}
-  .rel.dtors     : { *(.rel.dtors)	}
-  .rela.dtors    : { *(.rela.dtors)	}
-  .rel.bss       : { *(.rel.bss)		}
-  .rela.bss      : { *(.rela.bss)		}
-  .rel.plt       : { *(.rel.plt)		}
-  .rela.plt      : { *(.rela.plt)		}
-  .init          : { *(.init)	}
-  .plt : { *(.plt) }
   .text      :
   {
-    *(.text)
-    *(.got1)
+    *(.text*)
    } :text
     _etext = .;
     PROVIDE (etext = .);
     .rodata    :
    {
-    *(.eh_frame)
     *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*)))
   } :text
-  .fini      : { *(.fini)    } =0
-  .ctors     : { *(.ctors)   }
-  .dtors     : { *(.dtors)   }
 
   /* Read-write section, merged into data segment: */
   . = (. + 0x00FF) & 0xFFFFFF00;
@@ -83,23 +55,19 @@ SECTIONS
   PROVIDE (erotext = .);
   .reloc   :
   {
-    *(.got)
+    KEEP(*(.got))
     _GOT2_TABLE_ = .;
-    *(.got2)
+    KEEP(*(.got2))
     _FIXUP_TABLE_ = .;
-    *(.fixup)
+    KEEP(*(.fixup))
   }
   __got2_entries = (_FIXUP_TABLE_ - _GOT2_TABLE_) >> 2;
   __fixup_entries = (. - _FIXUP_TABLE_) >> 2;
 
   .data    :
   {
-    *(.data)
-    *(.data1)
-    *(.sdata)
-    *(.sdata2)
-    *(.dynamic)
-    CONSTRUCTORS
+    *(.data*)
+    *(.sdata*)
   }
   _edata  =  .;
   PROVIDE (edata = .);
@@ -138,7 +106,7 @@ SECTIONS
 
   .resetvec RESET_VECTOR_ADDRESS :
   {
-    *(.resetvec)
+    KEEP(*(.resetvec))
   } :text = 0xffff
 
   . = RESET_VECTOR_ADDRESS + 0x4;
@@ -157,9 +125,8 @@ SECTIONS
   __bss_start = .;
   .bss (NOLOAD)       :
   {
-   *(.sbss) *(.scommon)
-   *(.dynbss)
-   *(.bss)
+   *(.sbss*)
+   *(.bss*)
    *(COMMON)
   } :bss
 
-- 
1.7.3