linux-kernel - Re: [PATCH v2] perf test: Fix test trace+probe_vfs

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Date:   Fri, 31 Jan 2020 09:36:19 +0100
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Thomas Richter <tmricht@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH v2] perf test: Fix test trace+probe_vfs_getname.sh

Em Mon, Jan 20, 2020 at 02:20:11PM +0100, Thomas Richter escreveu:
> This test places a kprobe to function getname_flags() in the kernel
> which has the following prototype:
> 
>   struct filename *
>   getname_flags(const char __user *filename, int flags, int *empty)
> 
> Variable filename points to a filename located in user space memory.
> Looking at
> commit 88903c464321c ("tracing/probe: Add ustring type for user-space string")
> the kprobe should indicate that user space memory is accessed.

We can't just replace it, right? I.e. this should continue to work with
older kernels, i.e. the latest userspace tooling version should work
when installed in an older kernel, i.e. please just add more fallbacks
to cover the new cases.

- Arnaldo
 
> Fix this with a patch to specify user space memory access to
> parameter 'filename' and 'string' is replaced by 'ustring'.
> 
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
>  tools/perf/tests/shell/lib/probe_vfs_getname.sh | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/tests/shell/lib/probe_vfs_getname.sh b/tools/perf/tests/shell/lib/probe_vfs_getname.sh
> index 7cb99b433888..7ecf117651dd 100644
> --- a/tools/perf/tests/shell/lib/probe_vfs_getname.sh
> +++ b/tools/perf/tests/shell/lib/probe_vfs_getname.sh
> @@ -13,8 +13,8 @@ add_probe_vfs_getname() {
>  	local verbose=$1
>  	if [ $had_vfs_getname -eq 1 ] ; then
>  		line=$(perf probe -L getname_flags 2>&1 | egrep 'result.*=.*filename;' | sed -r 's/[[:space:]]+([[:digit:]]+)[[:space:]]+result->uptr.*/\1/')
> -		perf probe -q       "vfs_getname=getname_flags:${line} pathname=result->name:string" || \
> -		perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:string"
> +		perf probe -q       "vfs_getname=getname_flags:${line} pathname=result->uptr:ustring" || \
> +		perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:ustring"
>  	fi
>  }
>  
> -- 
> 2.21.0
> 

-- 

- Arnaldo