[Buildroot] [PATCH v2] Add support for the x86-64 x32 ABI for glibc and musl.
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Thu Aug 20 21:16:29 UTC 2015
Dear Guido Hatzsis,
Thanks for this contribution! Great to see someone working on x32
support!
On Thu, 20 Aug 2015 11:32:31 +0000, Guido Hatzsis wrote:
> x32 uses 32-bit pointers on the x84-64 linux target. The kernel needs
> to have CONFIG_X86_X32 enabled. For more information see:
> https://en.wikipedia.org/wiki/X32_ABI
>
> Changes v1 -> v2:
> Adding links for libx32 -> lib
> Added copying for libs to staging directory.
The changelog should go below the "---" sign after the Signed-off-by
statement, since we don't want the changelog to be kept in the final
commit.
> diff --git a/Makefile b/Makefile
> index b4cef3f..d50161f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -448,7 +448,11 @@ $(BUILD_DIR) $(TARGET_DIR) $(HOST_DIR) $(BINARIES_DIR) $(LEGAL_INFO_DIR) $(REDIS
> # We make a symlink lib32->lib or lib64->lib as appropriate
> # MIPS64/n32 requires lib32 even though it's a 64-bit arch.
> ifeq ($(BR2_ARCH_IS_64)$(BR2_MIPS_NABI32),y)
> +ifeq ($(BR2_X86_64_ABI_X32),y)
> +LIB_SYMLINK= libx32
Space after LIB_SYMLINK.
> +else
> LIB_SYMLINK = lib64
> +endif
> else
> LIB_SYMLINK = lib32
> endif
> diff --git a/arch/Config.in.x86 b/arch/Config.in.x86
> index 43f6abc..baaeae1 100644
> --- a/arch/Config.in.x86
> +++ b/arch/Config.in.x86
> @@ -268,3 +268,32 @@ config BR2_GCC_TARGET_ARCH
> default "c3" if BR2_x86_c3
> default "c3-2" if BR2_x86_c32
> default "geode" if BR2_x86_geode
> +
> +choice
> + prompt "Target ABI"
> + depends on BR2_x86_64
> + default BR2_X86_64_ABI_GCC
This option does not exist. You called it BR2_X86_64_ABI_GNU.
> + help
> + Application Binary Interface to use. The Application Binary
> + Interface describes the calling conventions (how arguments
> + are passed to functions, how the return value is passed, how
> + system calls are made, etc.).
> +
> +config BR2_X86_64_ABI_GNU
> + bool "gnu"
> + depends on BR2_x86_64
Not needed, the entire choice depends on BR2_x86_64.
> + help
> + This is the gnu ABI for x86-64 which has 64-bits wide pointers.
Indentation should be one tab + two spaces. Also, please indicate here
that something such as "This is the default ABI on x86-64, and should
be used unless you know what you are doing".
> +
> +config BR2_X86_64_ABI_X32
> + bool "x32"
> + depends on BR2_x86_64
Not needed.
> + help
> + The X32 ABI is x86-64 with 32 bit pointers. It runs in x86-64 mode
> + but as it has 32-bit pointers only 4 GB of RAM can be addressed.
> + https://en.wikipedia.org/wiki/X32_ABI
Please fix the indentation: one tab + two spaces.
> +
> +endchoice
> +
> +config BR2_GCC_TARGET_ABI
> + default "x32" if BR2_X86_64_ABI_X32
Do we need to provide a value for BR2_X86_64_ABI_GNU ? Or the ABI is
empty ?
> diff --git a/package/Makefile.in b/package/Makefile.in
> index 545694f..db2c0f0 100644
> --- a/package/Makefile.in
> +++ b/package/Makefile.in
> @@ -70,6 +70,11 @@ ABI := $(ABI)hf
> endif
> endif
>
> +# Only set the ABI for x86-64 x32.
> +ifeq ($(BR2_X86_64_ABI_X32),y)
> +ABI = x32
> +endif
> +
> # For FSL PowerPC there's SPE
> ifeq ($(BR2_powerpc_SPE),y)
> ABI = spe
> diff --git a/package/glibc/glibc.mk b/package/glibc/glibc.mk
> index cbfbf32..59a81d9 100644
> --- a/package/glibc/glibc.mk
> +++ b/package/glibc/glibc.mk
> @@ -117,7 +117,7 @@ endif
>
> define GLIBC_INSTALL_TARGET_CMDS
> for libs in $(GLIBC_LIBS_LIB); do \
> - $(call copy_toolchain_lib_root,$(STAGING_DIR)/,,lib,$$libs,/lib) ; \
> + $(call copy_toolchain_lib_root,$(STAGING_DIR)/,,$(if $(BR2_X86_64_ABI_X32),libx32,lib),$$libs,/lib) ; \
Hum, I'm not too happy with this. How does it work for normal x86-64
toolchains that want lib64 as the library directory?
> done
> endef
>
> diff --git a/package/uclibc/Config.in b/package/uclibc/Config.in
> index bf40a13..f4de98b 100644
> --- a/package/uclibc/Config.in
> +++ b/package/uclibc/Config.in
> @@ -3,6 +3,7 @@ if BR2_TOOLCHAIN_BUILDROOT_UCLIBC
> # For legal-info
> config BR2_PACKAGE_UCLIBC
> bool
> + depends on !BR2_X86_64_ABI_X32
Change not needed, since you're doing a change in
toolchain/toolchain-buildroot/Config.in to prevent selecting uClibc.
> default y
>
> comment "uClibc Options"
> diff --git a/toolchain/toolchain-buildroot/Config.in b/toolchain/toolchain-buildroot/Config.in
> index 13e2b15..a2ce5cd 100644
> --- a/toolchain/toolchain-buildroot/Config.in
> +++ b/toolchain/toolchain-buildroot/Config.in
> @@ -34,6 +34,7 @@ config BR2_TOOLCHAIN_BUILDROOT_UCLIBC
> BR2_mips || BR2_mipsel || BR2_mips64 || BR2_mips64el || \
> BR2_powerpc || BR2_sh2a || BR2_sh4 || BR2_sh4eb || \
> BR2_sparc || BR2_xtensa || BR2_x86_64
> + depends on !BR2_X86_64_ABI_X32
I would prefer the following change:
- BR2_sparc || BR2_xtensa || BR2_x86_64
+ BR2_sparc || BR2_xtensa || (BR2_x86_64 && BR2_X86_64_ABI_GNU)
Also, you need to:
* Verify that the musl C library supports the x32 ABI, and if not,
make it unavailable when x32 is selected.
* Make the relevant external x86-64 toolchains depend on
BR2_X86_64_ABI_GNU. You can have a look at how we handle ARM EABI
vs. ARM EABIhf toolchains to see how to do this.
* Ideally, we would need to check if we have packages that package
pre-built x86-64 binaries. And if we have such packages, then they
should probably depend on BR2_X86_64_ABI_GNU. Of course, I'm
assuming here that linking x32 binaries/libraries with x86-64 nu
binaries/libraries does not work.
Thanks!
Thomas
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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