linux-kernel - Re: [PATCH] perf probe: Fix failure to add multiple probes without debuginfo

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Date:	Thu, 19 Mar 2015 10:59:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	He Kuang <hekuang@...wei.com>
Cc:	masami.hiramatsu.pt@...achi.com, a.p.zijlstra@...llo.nl,
	mingo@...hat.com, namhyung@...nel.org, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf probe: Fix failure to add multiple probes without
 debuginfo

Em Thu, Mar 19, 2015 at 06:02:04PM +0800, He Kuang escreveu:
> Perf tries to find probe function addresses from map when debuginfo
> could not be found.
> 
> To the first added function, the value of ref_reloc_sym was set in
> maps__set_kallsyms_ref_reloc_sym() and can be obtained from
> host_machine->kmaps->maps. After that, new maps are added to
> host_machine->kmaps->maps in dso__load_kcore(), all these new added maps
> do not have a valid ref_reloc_sym.
> 
> When adding a second function, get_target_map() may get a map without
> valid ref_reloc_sym, and raise the error "Relocated base symbol is not
> found".
> 
> Fix this by getting ref_reloc_sym from machine->vmlinux_maps.

Can't this be solved by using the kernel_get_ref_reloc_sym(void) static
function in this same file?

- Arnaldo
 
> This problem can be reproduced as following:
> 
>   $ perf probe --add='sys_write' --add='sys_open'
>   Relocated base symbol is not found!
>     Error: Failed to add events.
> 
> After this patch:
> 
>   $ perf probe --add='sys_write' --add='sys_open'
>   Added new event:
>     probe:sys_write      (on sys_write)
> 
>   You can now use it in all perf tools, such as:
> 
>       perf record -e probe:sys_write -aR sleep 1
> 
>   Added new event:
>     probe:sys_open       (on sys_open)
> 
>   You can now use it in all perf tools, such as:
> 
>       perf record -e probe:sys_open -aR sleep 1
> 
> Signed-off-by: He Kuang <hekuang@...wei.com>
> ---
>  tools/perf/util/probe-event.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index c5e1338..75d41ee 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2540,7 +2540,19 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>  	}
>  
>  	if (!pev->uprobes && !pp->retprobe) {
> -		kmap = map__kmap(map);
> +		struct machine *machine;
> +		struct map *vmlinux_map = NULL;
> +
> +		if (map->groups && map->groups->machine) {
> +			machine = map->groups->machine;
> +			vmlinux_map = machine->vmlinux_maps[MAP__FUNCTION];
> +		}
> +
> +		if (vmlinux_map)
> +			kmap = map__kmap(vmlinux_map);
> +		else
> +			kmap = map__kmap(map);
> +
>  		reloc_sym = kmap->ref_reloc_sym;
>  		if (!reloc_sym) {
>  			pr_warning("Relocated base symbol is not found!\n");
> -- 
> 2.3.3.220.g9ab698f
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