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Re: [PATCH -tip 5/7] perf probe: Query basic types from debuginfo
- From: Arnaldo Carvalho de Melo <acme at infradead dot org>
- To: Masami Hiramatsu <mhiramat at redhat dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, lkml <linux-kernel at vger dot kernel dot org>, systemtap <systemtap at sources dot redhat dot com>, DLE <dle-develop at lists dot sourceforge dot net>, Paul Mackerras <paulus at samba dot org>, Peter Zijlstra <peterz at infradead dot org>, Mike Galbraith <efault at gmx dot de>, Frederic Weisbecker <fweisbec at gmail dot com>
- Date: Mon, 29 Mar 2010 17:51:43 -0300
- Subject: Re: [PATCH -tip 5/7] perf probe: Query basic types from debuginfo
- References: <20100329203736.2577.56018.stgit@localhost6.localdomain6> <20100329203829.2577.44718.stgit@localhost6.localdomain6>
Em Mon, Mar 29, 2010 at 04:38:29PM -0400, Masami Hiramatsu escreveu:
> +static void convert_variable_type(Dwarf_Die *vr_die,
> + struct kprobe_trace_arg *targ)
> +{
> + Dwarf_Die type;
> + char buf[16];
> + int ret;
> +
> + if (die_get_real_type(vr_die, &type) == NULL)
> + die("Failed to get a type information of %s.",
> + dwarf_diename(vr_die));
> +
> + ret = die_get_byte_size(&type) * 8;
> + if (ret) {
> + /* Check the bitwidth */
> + if (ret > MAX_BASIC_TYPE_BITS) {
> + pr_warning(" Warning: %s exceeds max-bitwidth."
> + " Cut down to %d bits.\n",
> + dwarf_diename(&type), MAX_BASIC_TYPE_BITS);
> + ret = MAX_BASIC_TYPE_BITS;
> + }
> +
> + ret = snprintf(buf, 16, "%c%d",
> + die_is_signed_type(&type) ? 's' : 'u', ret);
> + if (ret < 0 || ret >= 16)
> + die("Failed to convert variable type.");
> + targ->type = xstrdup(buf);
Question, should we use the equivalent to panic'ing the kernel in the
userspace bits in tools/?
I tend to see all code there as potentially part of a library, i.e. to
be callable by some unantecipated new tool or library that would rather
receive a return value telling it that the operation can't be performed
for some reason so that it can inform the user instead of having the
whole tool exit to the command line.
It may well be that some specific operation needs lots of resources but
many other don't, panic'c because the one that requires lots of
resources can't be performed, bringing down a gui/tui is really nasty.
Perhaps the answer will be the same as for when people added panic calls
in the kernel in the past, "you're screwed up anyway if that happens",
but it just feels wrong :-\
In the DWARF bits it has even the added twist namespace collapse with
DIE 8-)
- Arnaldo