linux-kernel - Re: [PATCH v9 0/4] Uprobes: Support SDT markers having reference count (semaphore)

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Message-Id: <1534836620.dp1nz6tfz0.naveen@linux.ibm.com>
Date:   Tue, 21 Aug 2018 13:04:17 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Song Liu <liu.song.a23@...il.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        Alexis Berlemont <alexis.berlemont@...il.com>,
        ananth@...ux.vnet.ibm.com, jolsa@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux@...linux.org.uk,
        open list <linux-kernel@...r.kernel.org>,
        linux-mips@...ux-mips.org, mhiramat@...nel.org, mingo@...hat.com,
        namhyung@...nel.org, Oleg Nesterov <oleg@...hat.com>,
        paul.burton@...s.com, Peter Zijlstra <peterz@...radead.org>,
        ralf@...ux-mips.org, Steven Rostedt <rostedt@...dmis.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v9 0/4] Uprobes: Support SDT markers having reference
 count (semaphore)

Song Liu wrote:
> I am testing the patch set with the following code:
> 
> #include <stdio.h>
> #include <unistd.h>
> 
> volatile short semaphore = 0;
> 
> int for_uprobe(int c)
> {
>         printf("%d\n", c + 10);
>         return c + 1;
> }
> 
> int main(int argc, char *argv[])
> {
>         for_uprobe(argc);
>         while (1) {
>                 sleep(1);
>                 printf("semaphore %d\n", semaphore);
>         }
> }
> 
> I created a uprobe on function for_uprobe(), that uses semaphore as
> reference counter:
> 
>   echo "p:uprobe_1 /root/a.out:0x49a(0x1036)" >> uprobe_events

Is that even valid? That _looks_ like a semaphore, but I'm not quite 
sure that it qualifies as an _SDT_ semaphore. Do you see this issue if 
you instead use the macros provided by <sys/sdt.h> to create SDT 
markers?


- Naveen