Re: [PATCH 08/17] tracing/probes: Split [ku]probes_fetch_type_table

From: Oleg Nesterov
Date: Mon Dec 02 2013 - 12:09:35 EST


On 12/02, Oleg Nesterov wrote:
>
> On 11/27, Namhyung Kim wrote:
> >
> > Use separate fetch_type_table for kprobes and uprobes. It currently
> > shares all fetch methods but some of them will be implemented
> > differently later.
>
> Hmm. This looks wrong, afaics...
>
> > static int parse_probe_arg(char *arg, const struct fetch_type *t,
> > struct fetch_param *f, bool is_return, bool is_kprobe)
> > {
> > + const struct fetch_type *ftbl;
> > unsigned long param;
> > long offset;
> > char *tmp;
> > - int ret;
> > + int ret = 0;
> >
> > - ret = 0;
> > + ftbl = is_kprobe ? kprobes_fetch_type_table : uprobes_fetch_type_table;
>
> OK, but what if, say, CONFIG_KPROBE_EVENT && !CONFIG_UPROBE_EVENT ?
> The kernel won't compile in this case?

Ah, wait, probably I was wrong. I didn't noticee that this patch
does

extern __weak const struct fetch_type kprobes_fetch_type_table[];
extern __weak const struct fetch_type uprobes_fetch_type_table[];

Is it the reason for "weak" ?

If yes, perhaps this deserves a comment or at least a note in the changelog.
Or is there another reason?

I am wondering if this should always work, with any toolchain. I simply
do not know what is the documented behaviour if a "weak" symbol is never
defined.

Oleg.

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