arm: make __bss_start and __bss_end__ compiler-generated

Turn __bss_start and __bss_end__ from linker-generated
to compiler-generated symbols, causing relocations for
these symbols to change type, from R_ARM_ABS32 to
R_ARM_RELATIVE.

This should have no functional impact, as it affects
references to __bss_start and __bss_end__ only before
relocation, and no such references are done.

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>

4 files changed, 58 insertions, 6 deletions

diff --git a/arch/arm/cpu/ixp/u-boot.lds b/arch/arm/cpu/ixp/u-boot.lds
index 81d954f..bba91d5 100644
--- a/arch/arm/cpu/ixp/u-boot.lds
+++ b/arch/arm/cpu/ixp/u-boot.lds
@@ -67,11 +67,17 @@ SECTIONS
 
 	_end = .;
 
-	.bss __rel_dyn_start (OVERLAY) : {
-		__bss_start = .;
+	.bss_start __rel_dyn_start (OVERLAY) : {
+		KEEP(*(.__bss_start));
+	}
+
+	.bss __bss_start (OVERLAY) : {
 		*(.bss*)
 		 . = ALIGN(4);
-		__bss_end__ = .;
+		 ___bssend___ = .;
+	}
+	.bss_end ___bssend___ (OVERLAY) : {
+		KEEP(*(.__bss_end__));
 	}
 
 	/DISCARD/ : { *(.dynstr*) }
diff --git a/arch/arm/cpu/u-boot.lds b/arch/arm/cpu/u-boot.lds
index e6b202b..e1bc8e7 100644
--- a/arch/arm/cpu/u-boot.lds
+++ b/arch/arm/cpu/u-boot.lds
@@ -81,11 +81,17 @@ SECTIONS
 		*(.mmutable)
 	}
 
-	.bss __rel_dyn_start (OVERLAY) : {
-		__bss_start = .;
+	.bss_start __rel_dyn_start (OVERLAY) : {
+		KEEP(*(.__bss_start));
+	}
+
+	.bss __bss_start (OVERLAY) : {
 		*(.bss*)
 		 . = ALIGN(4);
-		__bss_end__ = .;
+		 ___bssend___ = .;
+	}
+	.bss_end ___bssend___ (OVERLAY) : {
+		KEEP(*(.__bss_end__));
 	}
 
 	/DISCARD/ : { *(.dynstr*) }
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 57111af..11c2674 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -39,6 +39,7 @@ GLCOBJS	+= div0.o
 SOBJS-y += crt0.o
 
 ifndef CONFIG_SPL_BUILD
+COBJS-y += bss.o
 COBJS-y	+= board.o
 COBJS-y	+= bootm.o
 COBJS-$(CONFIG_SYS_L2_PL310) += cache-pl310.o
diff --git a/arch/arm/lib/bss.c b/arch/arm/lib/bss.c
new file mode 100644
index 0000000..7c0b154
--- /dev/null
+++ b/arch/arm/lib/bss.c
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2013 Albert ARIBAUD <albert.u.boot@aribaud.net>
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+/**
+ * These two symbols are declared in a C file so that the linker
+ * uses R_ARM_RELATIVE relocation, rather than the R_ARM_ABS32 one
+ * it would use if the symbols were defined in the linker file.
+ * Using only R_ARM_RELATIVE relocation ensures that references to
+ * the symbols are correct after as well as before relocation.
+ *
+ * We need a 0-byte-size type for these symbols, and the compiler
+ * does not allow defining objects of C type 'void'. Using an empty
+ * struct is allowed by the compiler, but causes gcc versions 4.4 and
+ * below to complain about aliasing. Therefore we use the next best
+ * thing: zero-sized arrays, which are both 0-byte-size and exempt from
+ * aliasing warnings.
+ */
+
+char __bss_start[0] __attribute__((used, section(".__bss_start")));
+char __bss_end__[0] __attribute__((used, section(".__bss_end__")));