linux-kernel - Re: Using a custom LDFLAG for all objects and binaries

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Date:   Mon, 11 May 2020 00:23:27 +0430
From:   Mahmood Naderan <mahmood.nt@...il.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: Using a custom LDFLAG for all objects and binaries

>OK, I suggest that you reorder the options like so:
>
>        KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE) --emit-relocs


I did that. After

$ make V=1
$ sudo make modules_install V=1
$ sudo make install

I grepped for "emit-relocs" in the log and saw many instances such as

  gcc -Wp,-MD,drivers/rtc/.rtc-ds1305.o.d  -nostdinc -isystem
/usr/lib/gcc/x86_64-linux-gnu/5/include -I./arch/x86/include
-I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi
-I./arch/x86/include/generated/uapi -I./include/uapi
-I./include/generated/uapi -include ./include/linux/kconfig.h -include
./include/linux/compiler_types.h -D__KERNEL__ -Wall -Wundef
-Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common
-fshort-wchar -Werror-implicit-function-declaration
-Wno-format-security -std=gnu89 -fno-PIE -mno-sse -mno-mmx -mno-sse2
-mno-3dnow -mno-avx -m64 -falign-jumps=1 -falign-loops=1 -mno-80387
-mno-fp-ret-in-387 -mpreferred-stack-boundary=3 -mskip-rax-setup
-mtune=generic -mno-red-zone -mcmodel=kernel -funit-at-a-time
-DCONFIG_X86_X32_ABI -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1
-DCONFIG_AS_CFI_SECTIONS=1 -DCONFIG_AS_FXSAVEQ=1 -DCONFIG_AS_SSSE3=1
-DCONFIG_AS_CRC32=1 -DCONFIG_AS_AVX=1 -DCONFIG_AS_AVX2=1
-DCONFIG_AS_AVX512=1 -DCONFIG_AS_SHA1_NI=1 -DCONFIG_AS_SHA256_NI=1
-pipe -Wno-sign-compare -fno-asynchronous-unwind-tables
-mindirect-branch=thunk-extern -mindirect-branch-register
-fno-jump-tables -fno-delete-null-pointer-checks -O2
--param=allow-store-data-races=0 -Wframe-larger-than=1024
-fstack-protector-strong -Wno-unused-but-set-variable
-fno-omit-frame-pointer -fno-optimize-sibling-calls
-fno-var-tracking-assignments -g -gdwarf-4 -pg -mrecord-mcount
-mfentry -DCC_USING_FENTRY -Wdeclaration-after-statement
-Wno-pointer-sign -fno-strict-overflow -fno-merge-all-constants
-fmerge-constants -fno-stack-check -fconserve-stack
-Werror=implicit-int -Werror=strict-prototypes -Werror=date-time
-Werror=incompatible-pointer-types -Werror=designated-init  -DMODULE
-DKBUILD_BASENAME='"rtc_ds1305"' -DKBUILD_MODNAME='"rtc_ds1305"' -c -o
drivers/rtc/rtc-ds1305.o drivers/rtc/rtc-ds1305.c
   ./tools/objtool/objtool check  --module --retpoline
"drivers/scsi/aacraid/dpcsup.o";

OR

  ld -r -m elf_x86_64 --emit-relocs  -z max-page-size=0x200000 -T
./scripts/module-common.lds  --build-id  -o
sound/usb/line6/snd-usb-line6.ko sound/usb/line6/snd-usb-line6.o
sound/usb/line6/snd-usb-line6.mod.o ;  true



I guess that all kernel modules are now use --emit-relocs.
I would like to be sure that libc and those files related to syscalls
are also using that.

I grepped for "libc.so" but it seems that there is no such match.
Did I miss something?


Regards,
Mahmood