xtensa: Fix linker script to include .literal sections

Fix resembles implementation from Marc Gauthier and Piet Denaly:

In the Xtensa architecture, assembly generates literals which must always
precede the code (the L32R instruction that loads them only uses negative
PC-relative offsets).  For any *.text section, literals are placed in a
corresponding *.literal section.  The linker script (vmlinux.lds) must
place these in the correct order.  It must also combine them, when the
*.text section can be larger than L32R's 256 kB range.

For example, this doesn't work:  *(.literal) *(.text) because L32R
instructions at the end of .text can't reach the literals.

The linker can solve this if they are combined in parentheses, like this:
       *(.literal .text)
because it is now allowed mix literals in .text to bring them in range.

None of this is done by standard vmlinux.lds.h macros such as TEXT_TEXT
and INIT_TEXT.  To avoid replicating the logic of that header file, we
instead post-process the generated linker script to convert *(xxx.text)
to *(xxx.literal xxx.text) for the following text sections:
       .text .ref.text .*init.text .*exit.text .text.*
using a sed script.  To do this we must override the default rule for
vmlinux.lds (see scripts/Makefile.build and the top-level Makefile)
to insert this extra step.

Signed-off-by: Marc Gauthier <marc@tensilica.com>
Signed-off-by: Pete Delaney <piet@tensilica.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

1 files changed, 18 insertions, 3 deletions

diff --git a/arch/xtensa/kernel/Makefile b/arch/xtensa/kernel/Makefile
index 7419dbccf027..fe3186de6a33 100644
--- a/arch/xtensa/kernel/Makefile
+++ b/arch/xtensa/kernel/Makefile
@@ -4,15 +4,30 @@
 
 extra-y := head.o vmlinux.lds
 
-
 obj-y := align.o entry.o irq.o coprocessor.o process.o ptrace.o \
          setup.o signal.o syscall.o time.o traps.o vectors.o platform.o  \
          pci-dma.o init_task.o io.o
 
-## windowspill.o
-
 obj-$(CONFIG_KGDB) += xtensa-stub.o
 obj-$(CONFIG_PCI) += pci.o
 obj-$(CONFIG_MODULES) += xtensa_ksyms.o module.o
 
+# In the Xtensa architecture, assembly generates literals which must always
+# precede the L32R instruction with a relative offset less than 256 kB.
+# Therefore, the .text and .literal section must be combined in parenthesis
+# in the linker script, such as: *(.literal .text).
+#
+# We need to post-process the generated vmlinux.lds scripts to convert
+# *(xxx.text) to  *(xxx.literal xxx.text) for the following text sections:
+#   .text .ref.text .*init.text .*exit.text .text.*
+#
+# Replicate rules in scripts/Makefile.build
+
+sed-y = -e 's/(\(\.[a-z]*it\|\.ref\|\)\.text)/(\1.literal \1.text)/g'   \
+        -e 's/(\(\.text\.[a-z]*\))/(\1.literal \1)/g'
+
+quiet_cmd__cpp_lds_S = LDS     $@
+      cmd__cpp_lds_S = $(CPP) $(cpp_flags) -D__ASSEMBLY__ $< | sed $(sed-y) >$@
 
+$(obj)/vmlinux.lds: $(src)/vmlinux.lds.S FORCE
+        $(call if_changed_dep,_cpp_lds_S)