Re: [Minios-devel] [UNIKRAFT PATCH 4/8] lib/uklibparam: Add linker script for parameter

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

On 3/15/19 6:06 PM, Sharan Santhanam wrote:
> This patch introduces a linker script to create linker
> section to place the library arguments meta-data.
>
> Signed-off-by: Sharan Santhanam <sharan.santhanam@xxxxxxxxx>
> ---
>   Makefile                      |  2 ++
>   lib/uklibparam/libparam.lds.S | 23 +++++++++++++++++++++++
>   plat/kvm/Linker.uk            |  2 +-
>   plat/linuxu/Linker.uk         |  3 ++-
>   plat/xen/Linker.uk            |  2 +-
>   support/build/Makefile.rules  | 35 +++++++++++++++++++++++++++++++++++
>   6 files changed, 64 insertions(+), 3 deletions(-)
>   create mode 100644 lib/uklibparam/libparam.lds.S
>
> diff --git a/Makefile b/Makefile
> index 8e81c64..e0fc145 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -198,6 +198,8 @@ UK_ALIBS:=
>   UK_ALIBS-y:=
>   UK_OLIBS:=
>   UK_OLIBS-y:=
> +UK_LDS:=
> +UK_LDS-y:=
>   UK_SRCS:=
>   UK_SRCS-y:=
>   UK_DEPS:=
> diff --git a/lib/uklibparam/libparam.lds.S b/lib/uklibparam/libparam.lds.S
> new file mode 100644
> index 0000000..3a9c920
> --- /dev/null
> +++ b/lib/uklibparam/libparam.lds.S
> @@ -0,0 +1,23 @@
> +#include <uk/config.h>
> +#include <uk/libparam.h>
> +
> +#define create_var(x,y) __STRINGCONCAT(x,y)
> +#ifdef UK_LIBPARAM_PREFIX
> +SECTIONS
> +{
> +       create_var(UK_LIBPARAM_PREFIX,__param_arg) : {
> +               _SECTION_START(
> +                               _LIB_PARAM_SECTION_NAME(UK_LIBPARAM_PREFIX,
> +                                                       PARAM_SECTION_SUFFIX)
> +                                 ) = .;
> +
> +               KEEP (*(create_var(UK_LIBPARAM_PREFIX,PARAM_SECTION_SUFFIX)))
> +
> +               _SECTION_STOP(
> +                               _LIB_PARAM_SECTION_NAME(UK_LIBPARAM_PREFIX,
> +                                                       PARAM_SECTION_SUFFIX)
> +                                 ) = .;
> +       }
> +}
> +INSERT AFTER .rodata
> +#endif /* UK_LIBPARAM_PREFIX */
So, the thing I don't like about this is that it creates a lot of 
additional sections in the ELF file: one when libparam is activated, and 
then another 2 for each library that has parameters. My understanding is 
you don't really care about the section itself, but rather use it to 
group all your variables together into a contiguous memory space, and to 
set the START and STOP variables to find it. There should be some way to 
achieving that without having to carry around those extra section 
headers, merging those sections into .rodata or another appropriate 
standard section in the last linking step... I just am not sure yet how.


> diff --git a/plat/kvm/Linker.uk b/plat/kvm/Linker.uk
> index f696e25..4b8b167 100644
> --- a/plat/kvm/Linker.uk
> +++ b/plat/kvm/Linker.uk
> @@ -15,7 +15,7 @@ EXTRA_LD_SCRIPT_FLAGS := $(addprefix 
> -Wl$(comma)-T,$(EXTRA_LD_SCRIPT-y))
>   
>   $(KVM_IMAGE): $(KVM_ALIBS) $(KVM_ALIBS-y) $(KVM_OLIBS) $(KVM_OLIBS-y) \
>                 $(UK_ALIBS) $(UK_ALIBS-y) $(UK_OLIBS) $(UK_OLIBS-y) \
> -              $(KVM_LDSCRIPT)
> +              $(UK_LDS) $(UK_LDS-y)
>         $(call build_cmd,LD,,$@.ld.o,\
>                $(LD) -r $(LIBLDFLAGS) $(LIBLDFLAGS-y) \
>                         $(KVM_LDFLAGS) $(KVM_LDFLAGS-y) \
> diff --git a/plat/linuxu/Linker.uk b/plat/linuxu/Linker.uk
> index dbdf9d9..f4387fa 100644
> --- a/plat/linuxu/Linker.uk
> +++ b/plat/linuxu/Linker.uk
> @@ -8,7 +8,8 @@ EXTRA_LD_SCRIPT_FLAGS := $(addprefix 
> -Wl$(comma)-T,$(EXTRA_LD_SCRIPT-y))
>   
>   $(LINUXU_IMAGE): $(LINUXU_ALIBS) $(LINUXU_ALIBS-y) \
>                  $(LINUXU_OLIBS) $(LINUXU_OLIBS-y) \
> -                $(UK_ALIBS) $(UK_ALIBS-y) $(UK_OLIBS) $(UK_OLIBS-y)
> +                $(UK_ALIBS) $(UK_ALIBS-y) $(UK_OLIBS) $(UK_OLIBS-y) \
> +                $(UK_LDS) $(UK_LDS-y)
>         $(call build_cmd,LD,,$@,\
>                $(LD) $(LDFLAGS) $(LDFLAGS-y) \
>                      $(LINUXU_LDFLAGS) $(LINUXU_LDFLAGS-y) \
> diff --git a/plat/xen/Linker.uk b/plat/xen/Linker.uk
> index 801f5e2..aea1089 100644
> --- a/plat/xen/Linker.uk
> +++ b/plat/xen/Linker.uk
> @@ -22,7 +22,7 @@ EXTRA_LD_SCRIPT_FLAGS := $(addprefix 
> -Wl$(comma)-T,$(EXTRA_LD_SCRIPT-y))
>   
>   $(XEN_IMAGE): $(XEN_ALIBS) $(XEN_ALIBS-y) $(XEN_OLIBS) $(XEN_OLIBS-y) \
>                 $(UK_ALIBS) $(UK_ALIBS-y) $(UK_OLIBS) $(UK_OLIBS-y) \
> -              $(XEN_LDSCRIPT)
> +              $(UK_LDS) $(UK_LDS-y)
>         $(call build_cmd,LD,,$@.ld.o,\
>                $(LD) -r $(LIBLDFLAGS) $(LIBLDFLAGS-y) \
>                         $(XEN_LDFLAGS) $(XEN_LDFLAGS-y) \
> diff --git a/support/build/Makefile.rules b/support/build/Makefile.rules
> index 04f2f0d..631fee3 100644
> --- a/support/build/Makefile.rules
> +++ b/support/build/Makefile.rules
> @@ -157,6 +157,26 @@ $(call addlib,$(1))
>   endif
>   endef
>   
> +# add_paramprefix $name $libname
> +define add_paramprefix =
> +$(eval UK_LIB_PARAM_LDS:=$(CONFIG_UK_BASE)/lib/uklibparam/libparam.lds.S)
> +$(eval $(call uc,$(2))_CFLAGS += -DUK_LIBPARAM_PREFIX=$(1))
> +$(eval $(call uc,$(2))_CXXFLAGS += -DUK_LIBPARAM_PREFIX=$(1))
> +$(eval $(call uc,$(2))_ASFLAGS += -DUK_LIBPARAM_PREFIX=$(1))
> +$(eval $(call uc,$(2))_LD_SCRIPT := $(call src2lds,$(2),$(UK_LIB_PARAM_LDS)))
> +endef
> +
> +# addlib_paramprefix $libname,$paramname(optional)
> +define addlib_paramprefix =
> +$(if $(2),\
> +$(eval name := $(2)),\
> +$(eval name := $(1)))
> +$(eval $(call add_paramprefix,$(name),$(1),$(call uc,$(1))))
> +$(eval EXTRA_LD_SCRIPT-$(CONFIG_LIBUKLIBPARAM) += $($(call uc,$(1))_LD_SCRIPT))
> +$(eval $(call uc,$(1))_SRCS-$(CONFIG_LIBUKLIBPARAM) += $(UK_LIB_PARAM_LDS))
> +$(eval $(call uc,$(1))_CLEAN-$(CONFIG_LIBUKLIBPARAM) += \
> +                                               $($(call uc,$(1))_LD_SCRIPT))
> +endef
>   
>   # addplatlib $platname,$libname
>   define addplatlib =
> @@ -173,6 +193,20 @@ $(if $(filter y,$(3)),$(call addplatlib,$(1),$(2)),)
>   endef
>   
>   
> +# addplatlib_paramprefix,$plat,$libname,$paramname(optional)
> +define addplatlib_paramprefix =
> +$(if $(3),\
> +$(eval name:=$(3)),\
> +$(eval name:=$(2)))
> +$(eval $(call add_paramprefix,$(name),$(2)))
> +$(eval $(call uc,$(1))_LD_SCRIPT-$(CONFIG_LIBUKLIBPARAM) +=\
> +                                               $($(call uc,$(2))_LD_SCRIPT))
> +$(eval $(call uc,$(2))_SRCS-$(CONFIG_LIBUKLIBPARAM) += \
> +                                               $(UK_LIB_PARAM_LDS))
> +$(eval $(call uc,$(2))_CLEAN-$(CONFIG_LIBUKLIBPARAM) +=\
> +                                               $($(call uc,$(2))_LD_SCRIPT))
> +endef
> +
>   
> ################################################################################
>   #
>   # Command calling
> @@ -420,6 +454,7 @@ $(3): $(2) | prepare
>         )
>   
>   UK_SRCS-y += $(2)
> +UK_LDS-y += $(3)
>   UK_DEPS-y += $(call out2dep,$(3))
>   $(eval $(call vprefix_lib,$(1),CLEAN-y) += $(call build_clean,$(3)) $(call 
> out2dep,$(3)))
>   endef
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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