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Commit 78f3cdfa authored by Chris Zankel's avatar Chris Zankel
Browse files

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: default avatarMarc Gauthier <marc@tensilica.com>
Signed-off-by: default avatarPete Delaney <piet@tensilica.com>
Signed-off-by: default avatarChris Zankel <chris@zankel.net>
parent 866e514d

arch/xtensa/kernel/Makefile

+18 −3
Original line number Diff line number Diff line
@@ -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)

arch/xtensa/kernel/vmlinux.lds.S

+1 −3
Original line number Diff line number Diff line
@@ -87,7 +87,7 @@ SECTIONS 
  {

    /* The HEAD_TEXT section must be the first section! */

    HEAD_TEXT

    *(.literal .text)

    TEXT_TEXT

    VMLINUX_SYMBOL(__sched_text_start) = .;

    *(.sched.literal .sched.text)

    VMLINUX_SYMBOL(__sched_text_end) = .;
@@ -139,8 +139,6 @@ SECTIONS 
  __init_begin = .;

  .init.text : {

  	_sinittext = .;

	*(.init.literal) *(.cpuinit.literal) 

	*(.devinit.literal) *(.meminit.literal)

	INIT_TEXT

	_einittext = .;

  }