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Date:   Wed, 6 May 2020 00:52:54 +0200
From:   Aurelien Jarno <aurelien@aurel32.net>
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        arnd@arndb.de
Subject: Re: [PATCH v4 7/8] powerpc/vdso32: implement clock_getres entirely
Message-ID: <20200505225254.GA471364@aurel32.net>
Mail-Followup-To: Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, arnd@arndb.de
References: <cover.1575273217.git.christophe.leroy@c-s.fr>
 <37f94e47c91070b7606fb3ec3fe6fd2302a475a0.1575273217.git.christophe.leroy@c-s.fr>
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Hi,

On 2019-12-02 07:57, Christophe Leroy wrote:
> clock_getres returns hrtimer_res for all clocks but coarse ones
> for which it returns KTIME_LOW_RES.
> 
> return EINVAL for unknown clocks.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/kernel/asm-offsets.c         |  3 +++
>  arch/powerpc/kernel/vdso32/gettimeofday.S | 19 +++++++++++--------
>  2 files changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
> index 0013197d89a6..90e53d432f2e 100644
> --- a/arch/powerpc/kernel/asm-offsets.c
> +++ b/arch/powerpc/kernel/asm-offsets.c
> @@ -413,7 +413,10 @@ int main(void)
>  	DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC);
>  	DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE);
>  	DEFINE(CLOCK_MONOTONIC_COARSE, CLOCK_MONOTONIC_COARSE);
> +	DEFINE(CLOCK_MAX, CLOCK_TAI);
>  	DEFINE(NSEC_PER_SEC, NSEC_PER_SEC);
> +	DEFINE(EINVAL, EINVAL);
> +	DEFINE(KTIME_LOW_RES, KTIME_LOW_RES);
>  
>  #ifdef CONFIG_BUG
>  	DEFINE(BUG_ENTRY_SIZE, sizeof(struct bug_entry));
> diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S
> index 9aafacea9c4a..20ae38f3a5a3 100644
> --- a/arch/powerpc/kernel/vdso32/gettimeofday.S
> +++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
> @@ -196,17 +196,20 @@ V_FUNCTION_END(__kernel_clock_gettime)
>  V_FUNCTION_BEGIN(__kernel_clock_getres)
>    .cfi_startproc
>  	/* Check for supported clock IDs */
> -	cmpwi	cr0,r3,CLOCK_REALTIME
> -	cmpwi	cr1,r3,CLOCK_MONOTONIC
> -	cror	cr0*4+eq,cr0*4+eq,cr1*4+eq
> -	bne	cr0,99f
> +	cmplwi	cr0, r3, CLOCK_MAX
> +	cmpwi	cr1, r3, CLOCK_REALTIME_COARSE
> +	cmpwi	cr7, r3, CLOCK_MONOTONIC_COARSE
> +	bgt	cr0, 99f
> +	LOAD_REG_IMMEDIATE(r5, KTIME_LOW_RES)
> +	beq	cr1, 1f
> +	beq	cr7, 1f
>  
>  	mflr	r12
>    .cfi_register lr,r12
>  	get_datapage	r3, r0
>  	lwz	r5, CLOCK_HRTIMER_RES(r3)
>  	mtlr	r12
> -	li	r3,0
> +1:	li	r3,0
>  	cmpli	cr0,r4,0
>  	crclr	cr0*4+so
>  	beqlr
> @@ -215,11 +218,11 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>  	blr
>  
>  	/*
> -	 * syscall fallback
> +	 * invalid clock
>  	 */
>  99:
> -	li	r0,__NR_clock_getres
> -	sc
> +	li	r3, EINVAL
> +	crset	so
>  	blr
>    .cfi_endproc
>  V_FUNCTION_END(__kernel_clock_getres)

Removing the syscall fallback looks wrong, and broke access to
per-processes clocks. With this change a few glibc tests now fail.

This can be reproduced by the simple code below:

| #include <errno.h>
| #include <stdio.h>
| #include <string.h>
| #include <sys/types.h>
| #include <time.h>
| #include <unistd.h>
| 
| int main()
| {
|     struct timespec res;
|     clockid_t ci;
|     int e;
|
|     e = clock_getcpuclockid(getpid(), &ci);
|     if (e) {
|         printf("clock_getcpuclockid returned %d\n", e);
|         return e;
|     }
|     e = clock_getres (ci, &res);
|     printf("clock_getres returned %d\n", e);
|     if (e) {
|         printf("  errno: %d, %s\n", errno, strerror(errno));
|     }
|
|     return e;
| }

Without this patch or with -m64, it returns:

| clock_getres returned 0

With this patch with -m32 it returns:

| clock_getres returned -1
|   errno: 22, Invalid argument

Regards,
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net