[Buildroot] [RFC PATCH 4/4] Add linker override to config options

[Arnout Vandecappelle]

On 24/07/2019 19:35, Joseph Kogut wrote:
> Signed-off-by: Joseph Kogut <joseph.kogut at gmail.com>

 Please make the commit message a bit more extensive. Actually, almost all of
the cover text could be put here.

> ---
>  Config.in                      | 27 +++++++++++++++++++++++++++
>  package/gcc/gcc.mk             |  3 ++-
>  package/glibc/glibc.mk         |  3 +++
>  toolchain/toolchain-wrapper.mk |  4 ++++
>  4 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/Config.in b/Config.in
> index 757ad1ca40..576d95305d 100644
> --- a/Config.in
> +++ b/Config.in
> @@ -318,6 +318,33 @@ config BR2_JLEVEL
>  	  Number of jobs to run simultaneously. If 0, determine
>  	  automatically according to number of CPUs on the host system.
>  
> +choice
> +	prompt "Default linker"
> +	default BR2_LINKER_BFD

 I think this option belongs in the toolchain menu, under the toolchain generic
options.

> +	help
> +	  Choose the default linker
> +	  Individual packages may override this choice

 Please end sentences with a period, and if it's intended as two paragraphs, add
an empty line between them.

> +
> +config BR2_LINKER_BFD
> +	bool "GNU ld"
> +	help
> +	  GNU GCC linker
> +
> +config BR2_LINKER_LLD
> +	bool "LLVM LLD"
> +	select BR2_PACKAGE_HOST_LLD

 If this requires gcc 9+, you should add

	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_9

> +	help
> +	  Clang/LLVM linker
> +
> +	  Offers a faster link times compared to GNU linkers such as ld.bfd and
> +	  ld.gold.
> +
> +	  NOTE: This option requires building LLVM, which is time consuming itself.
> +
> +	  https://lld.llvm.org/
> +
> +endchoice
> +
>  config BR2_CCACHE
>  	bool "Enable compiler cache"
>  	help
> diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
> index 46ad16df13..aef0038639 100644
> --- a/package/gcc/gcc.mk
> +++ b/package/gcc/gcc.mk
> @@ -85,7 +85,8 @@ HOST_GCC_COMMON_DEPENDENCIES = \
>  	host-gmp \
>  	host-mpc \
>  	host-mpfr \
> -	$(if $(BR2_BINFMT_FLAT),host-elf2flt)
> +	$(if $(BR2_BINFMT_FLAT),host-elf2flt) \
> +	$(if $(BR2_LINKER_LLD),host-lld)

 I think it's not really needed by gcc itself, but only by the packages that
will add the -fuse-ld flag, right? Then I think it's more appropriate to add the
dependency to the toolchain (virtual) package. That way, we also support
external toolchains.

>  
>  HOST_GCC_COMMON_CONF_OPTS = \
>  	--target=$(GNU_TARGET_NAME) \
> diff --git a/package/glibc/glibc.mk b/package/glibc/glibc.mk
> index f8d8c1bd87..1c06028241 100644
> --- a/package/glibc/glibc.mk
> +++ b/package/glibc/glibc.mk
> @@ -32,6 +32,9 @@ GLIBC_LICENSE_FILES = COPYING COPYING.LIB LICENSES
>  # glibc is part of the toolchain so disable the toolchain dependency
>  GLIBC_ADD_TOOLCHAIN_DEPENDENCY = NO
>  
> +# Glibc requires ld.bfd
> +GLIBC_MAKE_ENV += BR2_NO_LINKER_OVERRIDE=1
> +
>  # Before glibc is configured, we must have the first stage
>  # cross-compiler and the kernel headers
>  GLIBC_DEPENDENCIES = host-gcc-initial linux-headers host-bison host-gawk \
> diff --git a/toolchain/toolchain-wrapper.mk b/toolchain/toolchain-wrapper.mk
> index ca66fa7ba4..ff7a7ab448 100644
> --- a/toolchain/toolchain-wrapper.mk
> +++ b/toolchain/toolchain-wrapper.mk
> @@ -16,6 +16,10 @@ endif
>  TOOLCHAIN_WRAPPER_ARGS = $($(PKG)_TOOLCHAIN_WRAPPER_ARGS)
>  TOOLCHAIN_WRAPPER_ARGS += -DBR_SYSROOT='"$(STAGING_SUBDIR)"'
>  
> +ifeq ($(BR2_LINKER_LLD),y)
> +TOOLCHAIN_WRAPPER_ARGS += -DBR_LINKER='"lld"'
> +endif
> +
>  TOOLCHAIN_WRAPPER_OPTS = \
>  	$(call qstrip,$(BR2_SSP_OPTION)) \
>  	$(call qstrip,$(BR2_TARGET_OPTIMIZATION))


 I think two additional patches will be needed:

1. An update to the manual that explains how to disable lld in the
adding-packages section.

2. An update to genrandconfig that makes sure the LLD option gets tested in the
autobuilders.


 Regards,
 Arnout