linux-kernel - Re: [PATCH v4 10/12] arm64: vdso: replace gettimeofday.S with global vgettimeofday.C

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Message-ID: <7775cc5e-4a24-1e33-aae5-6181ca018d80@android.com>
Date:   Wed, 1 Nov 2017 15:14:03 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     linux-kernel@...r.kernel.org
Cc:     James Morse <james.morse@....com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        John Stultz <john.stultz@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Pinski <apinski@...ium.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, Jon Masters <jcm@...hat.com>
Subject: Re: [PATCH v4 10/12] arm64: vdso: replace gettimeofday.S with global
 vgettimeofday.C

On 10/31/2017 11:32 AM, Mark Salyzyn wrote:
> . . .
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index 62c84f7cb01b..0925f8908dcb 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -5,18 +5,26 @@
>   # Heavily based on the vDSO Makefiles for other archs.
>   #
>   
> -obj-vdso := gettimeofday.o note.o sigreturn.o
> +obj-vdso := vgettimeofday.o note.o sigreturn.o
>   
>   # Build rules
>   targets := $(obj-vdso) vdso.so vdso.so.dbg
>   obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
>   
> -ccflags-y := -shared -fno-common -fno-builtin
> +ccflags-y := -shared -fno-common -fno-builtin -fno-stack-protector
> +ccflags-y += -DDISABLE_BRANCH_PROFILING
>   ccflags-y += -nostdlib -Wl,-soname=linux-vdso.so.1 \
>   		$(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
>   
> +# Force -O2 to avoid libgcc dependencies
> +CFLAGS_REMOVE_vgettimeofday.o = -pg -Os
> +CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny
> +
This last stanza breaks clang builds. Suggested fix is:

@@ -18,7 +18,11 @@ ccflags-y += -nostdlib -Wl,-soname=linux-vdso.so.1 \

  # Force -O2 to avoid libgcc dependencies
  CFLAGS_REMOVE_vgettimeofday.o = -pg -Os
+ifeq ($(cc-name),clang)
+CFLAGS_vgettimeofday.o = -O2
+else
  CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny
+endif

  # Disable gcov profiling for VDSO code
  GCOV_PROFILE := n

Holding off respin or followup patch until after we get a response from 
Jon Masters <jcm@...dhat.com> on their QE tests on this patch series.

-- Mark