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From: Mats Kindahl <mats.kindahl@gmail.com>
To: cocci@inria.fr
Subject: [cocci] Symbolic names in iso-files
Date: Sat, 24 Aug 2024 14:23:33 +0200	[thread overview]
Message-ID: <983f5490-ee27-4558-832f-6d5af7344b79@gmail.com> (raw)

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Hi all,

In some code, there are macros used for different purposes. One typical 
case is having a "foreach" macro, but this is covered using "iterator" 
so that you can deal with code like this:

    static Jsonb *BuildJsonObject(List *items) {
       ListCell *cell;
       JsonbParseState *state = NULL;
       JsonbValue *value;

       pushJsonbValue(&state, WJB_BEGIN_OBJECT, NULL);
       foreach (cell, items) {
         KVItem *item = (KVItem *)lfirst(cell);
         AddJsonField(&state, item->key, item->value);
       }
       value = pushJsonbValue(&state, WJB_END_OBJECT, NULL);

       return JsonbValueToJsonb(value);
    }

However, if you want to make sure to deal with resource allocation and 
make sure that you release a short-lived lock, for example (grossly 
simplified, just to demonstrate the problem):

    @@
    expression lock, mode;
    @@
       LWLockAcquire(lock, mode);
       ... when exists
    (
       LWLockRelease(lock);
    |
    + LWLockRelease(lock);
       return;
    )

If fails miserably with this code:

    Datum start_worker(PG_FUNCTION_ARGS) {
       pid_t pid;

       if (!autoprewarm)
         ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("autoprewarm is disabled")));

       apw_init_shmem();
       LWLockAcquire(&apw_state->lock, LW_EXCLUSIVE);
       pid = apw_state->bgworker_pid;

       if (pid != InvalidPid)
         ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("autoprewarm worker is already running
    under PID %d",
                                (int)pid)));

       apw_start_leader_worker();

       PG_RETURN_VOID();
    }

Giving the patch, where the call to LWLockRelease should be before the 
PG_RETURN_VOID:

    --- code/lwlock.c
    +++ /tmp/cocci-output-12611-ff946d-lwlock.c
    @@ -18,6 +18,7 @@ Datum start_worker(PG_FUNCTION_ARGS) {
       apw_start_leader_worker();

       PG_RETURN_VOID();
    +  LWLockRelease(&apw_state->lock);
    }

Since this is such a common construct, and you do not want to deal with 
this for every potential case, this seems like an obvious case for using 
an iso-file, so I created one that looks like this, with the idea that 
we support replacing "PG_RETURN_VOID()" with just a "return".

    Statement
    @ pg_return @
    @@
       PG_RETURN_VOID() => return

However, this fails with the following error message:

    mats@abzu:~/lang/cocci/hacks$ spatch --sp-file lwlock.cocci
    code/lwlock.c
    init_defs_builtins: /usr/lib/coccinelle/standard.h
    iso main: parse error:
      File "./postgres.iso", line 4, column 19, charpos = 46
      around = '=>',
      whole content =   PG_RETURN_VOID() => return

Which I suppose mean that there is no support for handling anything but 
standard tokens in an .iso file.

Have I misunderstood the situation and this is already supported in some 
way?

Are there any plans that add such support to the ISO grammar?

Best wishes,
Mats Kindahl, Timescale

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next             reply	other threads:[~2024-08-24 12:23 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-08-24 12:23 Mats Kindahl [this message]
2024-08-24 12:56 ` [cocci] Symbolic names in iso-files Julia Lawall
2024-08-24 13:00   ` Mats Kindahl
2024-08-24 18:09     ` Julia Lawall
2024-08-25  7:25       ` Mats Kindahl

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