ELF/MIPS build fix

CONFIG_MIPS32_N32=y but CONFIG_BINFMT_ELF disabled results in the
following linker errors:

  arch/mips/built-in.o: In function `elf_core_dump':
  binfmt_elfn32.c:(.text+0x23dbc): undefined reference to `elf_core_extra_phdrs'
  binfmt_elfn32.c:(.text+0x246e4): undefined reference to `elf_core_extra_data_size'
  binfmt_elfn32.c:(.text+0x248d0): undefined reference to `elf_core_write_extra_phdrs'
  binfmt_elfn32.c:(.text+0x24ac4): undefined reference to `elf_core_write_extra_data'

CONFIG_MIPS32_O32=y but CONFIG_BINFMT_ELF disabled results in the following
linker errors:

  arch/mips/built-in.o: In function `elf_core_dump':
  binfmt_elfo32.c:(.text+0x28a04): undefined reference to `elf_core_extra_phdrs'
  binfmt_elfo32.c:(.text+0x29330): undefined reference to `elf_core_extra_data_size'
  binfmt_elfo32.c:(.text+0x2951c): undefined reference to `elf_core_write_extra_phdrs'
  binfmt_elfo32.c:(.text+0x29710): undefined reference to `elf_core_write_extra_data'

This is because binfmt_elfn32 and binfmt_elfo32 are using symbols from
elfcore but for these configurations elfcore will not be built.

Fixed by making elfcore selectable by a separate config symbol which
unlike the current mechanism can also be used from other directories
than kernel/, then having each flavor of ELF that relies on elfcore.o,
select it in Kconfig, including CONFIG_MIPS32_N32 and CONFIG_MIPS32_O32
which fixes this issue.

Link: http://lkml.kernel.org/r/20160520141705.GA1913@linux-mips.orgSigned-off-by: Ralf Baechle <ralf@linux-mips.org>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/mips/Kconfig

@@ -3117,6 +3117,7 @@ config MIPS32_N32
 config BINFMT_ELF32
 	bool
 	default y if MIPS32_O32 || MIPS32_N32
+	select ELFCORE
 
 endmenu
 

fs/Kconfig.binfmt

 config BINFMT_ELF
 	bool "Kernel support for ELF binaries"
 	depends on MMU && (BROKEN || !FRV)
+	select ELFCORE
 	default y
 	---help---
 	  ELF (Executable and Linkable Format) is a format for libraries and
@@ -26,6 +27,7 @@ config BINFMT_ELF
 config COMPAT_BINFMT_ELF
 	bool
 	depends on COMPAT && BINFMT_ELF
+	select ELFCORE
 
 config ARCH_BINFMT_ELF_STATE
 	bool
@@ -34,6 +36,7 @@ config BINFMT_ELF_FDPIC
 	bool "Kernel support for FDPIC ELF binaries"
 	default y
 	depends on (FRV || BLACKFIN || (SUPERH32 && !MMU) || C6X)
+	select ELFCORE
 	help
 	  ELF FDPIC binaries are based on ELF, but allow the individual load
 	  segments of a binary to be located in memory independently of each
@@ -43,6 +46,11 @@ config BINFMT_ELF_FDPIC
 
 	  It is also possible to run FDPIC ELF binaries on MMU linux also.
 
+config ELFCORE
+	bool
+	help
+	  This option enables kernel/elfcore.o.
+
 config CORE_DUMP_DEFAULT_ELF_HEADERS
 	bool "Write ELF core dumps with partial segments"
 	default y

kernel/Makefile

@@ -91,9 +91,7 @@ obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
 obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
 obj-$(CONFIG_TRACEPOINTS) += tracepoint.o
 obj-$(CONFIG_LATENCYTOP) += latencytop.o
-obj-$(CONFIG_BINFMT_ELF) += elfcore.o
-obj-$(CONFIG_COMPAT_BINFMT_ELF) += elfcore.o
-obj-$(CONFIG_BINFMT_ELF_FDPIC) += elfcore.o
+obj-$(CONFIG_ELFCORE) += elfcore.o
 obj-$(CONFIG_FUNCTION_TRACER) += trace/
 obj-$(CONFIG_TRACING) += trace/
 obj-$(CONFIG_TRACE_CLOCK) += trace/