Re: [PATCH -tip 5/7] perf probe: Query basic types from debuginfo

Masami Hiramatsu
2010-03-29T21:22:54Z

Arnaldo Carvalho de Melo wrote:
> 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.

OK, so that you want to see

ret = library_func();
if (ret < 0) /* Something wrong happened */
return ret;

instead of

library_func();
hopefully_executed_next_func();

> 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.

Hmm, agreed. But I'd like to have some API for storing dying^H^H^H^H^Herror
message. (maybe can we use setjump/longjump approach - like try/cache - for die()?)

Thank you,

>
> 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
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