On Fri, May 20, 2016 at 04:17:05PM +0200, Ralf Baechle wrote:
> 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.
> 
> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

FWIW this looks good to me,

Reviewed-by: James Hogan <james.hogan@imgtec.com>

Cheers
James

> ---
>  arch/mips/Kconfig | 1 +
>  fs/Kconfig.binfmt | 8 ++++++++
>  kernel/Makefile   | 4 +---
>  3 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 5663f41..f19e15c 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -3116,6 +3116,7 @@ config MIPS32_N32
>  config BINFMT_ELF32
>  	bool
>  	default y if MIPS32_O32 || MIPS32_N32
> +	select ELFCORE
>  
>  endmenu
>  
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index 2d0cbbd..72c0335 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -1,6 +1,7 @@
>  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
> diff --git a/kernel/Makefile b/kernel/Makefile
> index f0c40bf..e2ec54e 100644
> --- a/kernel/Makefile
> +++ b/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/