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Re: [Minios-devel] [UNIKRAFT PATCH v2 1/2] build: Use GCC for linking

Hi Sharan,

On 14.05.2018 14:12, Sharan Santhanam wrote:

Hello Simon,

Please find the review comments below:


On 05/11/2018 04:24 PM, Simon Kuenzer wrote:

Instead of using `ld` directly, `gcc` is used for linking.
`gcc` is going to call `ld` but provides further
optimizations options that could be used for building
images later (e.g., LTO).

* The gcc wiki suggests this:
https://gcc.gnu.org/wiki/LinkTimeOptimizationFAQ#ar.2C_nm_and_ranlib
"If you try to build bigger projects with -flto you have to make sure that you use a version of binutils that supports gcc's liblto_plugin. Since version 4.9 gcc produces slim object files that only contain the intermediate representation. In order to handle archives of these objects you have to use the gcc wrappers: gcc-ar, gcc-nm and gcc-ranlib. (The next version of binutils will support automatic loading of the liblto_plugin.) "
If we using the changing ld to gcc, we should also use the rest of the binutils utility as suggested.
Thanks for pointing this out. I agree, we should use also the rest of the build tools. I am going to prepare a v2 where I replace nm with gcc-nm, and ar with gcc-ar. We are not using ranlib for now. 




* The following gcc documentation list the possible optimization options.
https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
The -flto and -fwhole-program option are incompatible.  There are also other compiler optimization option used in combination with -flto. Do we consider those option as a part of this patch or do we support those options.
I think this comment is related to patch 2/2 that introduces LTO, right? I intended to introduce initial LTO support as a trial first (default is off) and I am expecting to have patches later that provide more configuration options if needed. 


Signed-off-by: Simon Kuenzer<simon.kuenzer@xxxxxxxxx>
---
  Makefile              |  2 +-
  Makefile.uk           |  8 ++++----
  plat/kvm/Linker.uk    |  8 ++++----
  plat/linuxu/Linker.uk |  2 +-
  plat/xen/Linker.uk    | 16 ++++++++--------
  5 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/Makefile b/Makefile
index b177bff..23ebe21 100644
--- a/Makefile
+++ b/Makefile
@@ -387,7 +387,7 @@ CROSS_COMPILE := $(CROSS_COMPILE:"%"=%)
  include $(UK_BASE)/arch/$(UK_ARCH)/Compiler.uk
# Make variables (CC, etc...) 
-LD             := $(CROSS_COMPILE)ld
+LD             := $(CROSS_COMPILE)gcc
  CC            := $(CROSS_COMPILE)gcc
  CPP           := $(CC)
  CXX           := $(CPP)
diff --git a/Makefile.uk b/Makefile.uk
index 5855b40..c540ada 100644
--- a/Makefile.uk
+++ b/Makefile.uk
@@ -20,8 +20,8 @@ CXXINCLUDES += -nostdinc -nostdlib -I$(UK_BASE)/include
  # Set the text and data sections to be readable and writable. Also,
  # do not page-align the data segment. If the output format supports
  # Unix style magic numbers, mark the output as OMAGIC.
-LIBLDFLAGS  += --omagic -r
-LDFLAGS            += --omagic
+LIBLDFLAGS  += -nostdinc -nostdlib -Wl,--omagic -Wl,-r
+LDFLAGS     += -nostdinc -nostdlib -Wl,--omagic -Wl,--build-id=none
CFLAGS-$(OPTIMIZE_NONE) += -O0 -fno-optimize-sibling-calls -fno-tree-vectorize 
  CXXFLAGS-$(OPTIMIZE_NONE)          += -O0 -fno-optimize-sibling-calls 
-fno-tree-vectorize
@@ -32,12 +32,12 @@ CXXFLAGS-$(OPTIMIZE_SIZE)          += -Os
CFLAGS-$(OPTIMIZE_DEADELIM) += -fdata-sections -ffunction-sections 
  CXXFLAGS-$(OPTIMIZE_DEADELIM)      += -fdata-sections -ffunction-sections
-LDFLAGS-$(OPTIMIZE_DEADELIM)       += --gc-sections
+LDFLAGS-$(OPTIMIZE_DEADELIM)       += -Wl,--gc-sections
ifneq ($(DEBUG_SYMBOLS),y) 
  CFLAGS                             += -g0
  CXXFLAGS                           += -g0
-LDFLAGS-y                         += --strip-debug
+LDFLAGS-y                         += -Wl,--strip-debug
  else
  CFLAGS-$(DEBUG_SYMBOLS_LVL1)       += -g1
  CXXFLAGS-$(DEBUG_SYMBOLS_LVL1)     += -g1
diff --git a/plat/kvm/Linker.uk b/plat/kvm/Linker.uk
index 7957b7a..a91a786 100644
--- a/plat/kvm/Linker.uk
+++ b/plat/kvm/Linker.uk
@@ -1,6 +1,6 @@
  ifeq (x86_64,$(UK_ARCH))
-KVM_LDSCRIPT  := $(UK_BASE)/plat/kvm/x86/link64.ld
-KVM_LDFLAGS-y += -m elf_x86_64
+KVM_LDSCRIPT  := -Wl,-T,$(UK_BASE)/plat/kvm/x86/link64.ld
+KVM_LDFLAGS-y += -Wl,-m,elf_x86_64
  endif
## 
@@ -10,12 +10,12 @@ KVM_IMAGE := $(BUILD_DIR)/$(UK_NAME)_kvm-$(UK_ARCH)
$(KVM_IMAGE): $(KVM_LINK) $(KVM_LINK-y) $(UK_LINK) $(UK_LINK-y) 
        $(call build_cmd,LD,,$@.ld.o,\
-              $(LD) $(LIBLDFLAGS) $(LIBLDFLAGS-y) $(KVM_LDFLAGS) 
$(KVM_LDFLAGS-y) $^ -o $@.ld.o)
+              $(LD) -r $(LIBLDFLAGS) $(LIBLDFLAGS-y) $(KVM_LDFLAGS) 
$(KVM_LDFLAGS-y) $^ -o $@.ld.o)
        $(call build_cmd,OBJCOPY,,$@.o,\
               $(OBJCOPY) -w -G kvmos_* -G _libkvmplat_entry $@.ld.o $@.o)
  ifeq (x86_64,$(UK_ARCH))
        $(call build_cmd,LD,,$@,\
-              $(LD) $(LDFLAGS) $(LDFLAGS-y) $(KVM_LDFLAGS) $(KVM_LDFLAGS-y) -T 
$(KVM_LDSCRIPT) $@.o -o $@)
+              $(LD) $(LDFLAGS) $(LDFLAGS-y) $(KVM_LDFLAGS) $(KVM_LDFLAGS-y) 
$(KVM_LDSCRIPT) $@.o -o $@)
  ifeq ($(OPTIMIZE_DBGFILE),y)
        $(call build_cmd,OBJCOPY,,$@.dbg,\
               $(OBJCOPY) --only-keep-debug $@ $@.dbg)
diff --git a/plat/linuxu/Linker.uk b/plat/linuxu/Linker.uk
index 16a5b15..d50401f 100644
--- a/plat/linuxu/Linker.uk
+++ b/plat/linuxu/Linker.uk
@@ -1,4 +1,4 @@
-LINUXU_LDFLAGS-y += -e_liblinuxuplat_start
+LINUXU_LDFLAGS-y += -Wl,-e,_liblinuxuplat_start
## 
  ## Link image
diff --git a/plat/xen/Linker.uk b/plat/xen/Linker.uk
index c0851c3..3890196 100644
--- a/plat/xen/Linker.uk
+++ b/plat/xen/Linker.uk
@@ -1,16 +1,16 @@
  ifeq (x86_64,$(UK_ARCH))
-XEN_LDSCRIPT  := $(UK_BASE)/plat/xen/x86/link64.ld
-XEN_LDFLAGS-y += -m elf_x86_64
+XEN_LDSCRIPT  := -Wl,-T,$(UK_BASE)/plat/xen/x86/link64.ld
+XEN_LDFLAGS-y += -Wl,-m,elf_x86_64
  endif
  ifeq (x86_32,$(UK_ARCH))
-XEN_LDSCRIPT  := $(UK_BASE)/plat/xen/x86/link32.ld
-XEN_LDFLAGS-y += -m elf_x86_32
+XEN_LDSCRIPT  := -Wl,-T,$(UK_BASE)/plat/xen/x86/link32.ld
+XEN_LDFLAGS-y += -Wl,-m,elf_x86_32
  endif
  ifeq (arm_64,$(UK_ARCH))
-XEN_LDSCRIPT  := $(UK_BASE)/plat/xen/arm/link64.ld
+XEN_LDSCRIPT  := -Wl,-T,$(UK_BASE)/plat/xen/arm/link64.ld
  endif
  ifeq (arm,$(UK_ARCH))
-XEN_LDSCRIPT  := $(UK_BASE)/plat/xen/arm/link32.ld
+XEN_LDSCRIPT  := -Wl,-T,$(UK_BASE)/plat/xen/arm/link32.ld
  endif
## 
@@ -25,7 +25,7 @@ $(XEN_IMAGE): $(XEN_LINK) $(XEN_LINK-y) $(UK_LINK) 
$(UK_LINK-y)
               $(OBJCOPY) -w -G xenos_* -G _libxenplat_start $@.ld.o $@.o)
  ifeq (arm,$(UK_ARCH))
        $(call build_cmd,LD,,$@.elf,\
-              $(LD) $(LDFLAGS) $(LDFLAGS-y) $(XEN_LDFLAGS) $(XEN_LDFLAGS-y) -T 
$(XEN_LDSCRIPT) $@.o -o $@.elf)
+              $(LD) $(LDFLAGS) $(LDFLAGS-y) $(XEN_LDFLAGS) $(XEN_LDFLAGS-y) 
$(XEN_LDSCRIPT) $@.o -o $@.elf)
  ifeq ($(OPTIMIZE_DBGFILE),y)
        $(call build_cmd,OBJCOPY,,$@.dbg,\
               $(OBJCOPY) --only-keep-debug $@.elf $@.dbg)
@@ -44,7 +44,7 @@ endif
               $(GZIP) -f -9 -c $@ >$@.gz)
  else
        $(call build_cmd,LD,,$@,\
-              $(LD) $(LDFLAGS) $(LDFLAGS-y) $(XEN_LDFLAGS) $(XEN_LDFLAGS-y) -T 
$(XEN_LDSCRIPT) $@.o -o $@)
+              $(LD) $(LDFLAGS) $(LDFLAGS-y) $(XEN_LDFLAGS) $(XEN_LDFLAGS-y) 
$(XEN_LDSCRIPT) $@.o -o $@)
  ifeq ($(OPTIMIZE_DBGFILE),y)
        $(call build_cmd,OBJCOPY,,$@.dbg,\
               $(OBJCOPY) --only-keep-debug $@ $@.dbg)


The rest of the code looks fine.

Thanks & Regards
Sharan Santhanam


Thanks,

Simon

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