git/list[1] front-page[2] threads[3] people[4] search[5] about
 

excluding a function from coccinelle transformation

From
Jeff King <peff@peff.net>
Date
Aug 24, 2018, 06:42 UTC
Message-ID
<20180824064228.GA3183@sigill.intra.peff.net>

In Git's Coccinelle patches, we sometimes want to suppress a transformation inside a particular function. For example, in finding conversions of hashcmp() to oidcmp(), we should not convert the call in oidcmp() itself, since that would cause infinite recursion. We write the semantic patch like this:

  @@
  identifier f != oidcmp;
  expression E1, E2;
  @@
    f(...) {...
  - hashcmp(E1->hash, E2->hash)
  + oidcmp(E1, E2)
    ...}

This catches some cases, but not all. For instance, there's one case in sequencer.c which it does not convert. Now here's where it gets weird. If I instead use the angle-bracket form of ellipses, like this:

  @@
  identifier f != oidcmp;
  expression E1, E2;
  @@
    f(...) {<...
  - hashcmp(E1->hash, E2->hash)
  + oidcmp(E1, E2)
    ...>}

then we do generate the expected diff! Here's a much more cut-down source file that demonstrates the same behavior:

  int foo(void)
  {
    if (1)
      if (!hashcmp(x, y))
        return 1;
    return 0;
  }

If I remove the initial "if (1)" then a diff is generated with either semantic patch (and the particulars of the "if" are not important; the same thing happens if it's a while-loop. The key thing seems to be that the code is not in the top-level block of the function).

And here's some double-weirdness. I get those results with spatch 1.0.4, which is what's in Debian unstable. If I then upgrade to 1.0.6 from Debian experimental, then _neither_ patch produces any results! Instead I get:

  init_defs_builtins: /usr/lib/coccinelle/standard.h
  (ONCE) Expected tokens oidcmp hashcmp hash
  Skipping:foo.c
(whereas before, even the failing case said "HANDLING: foo.c").

And then one final check: I built coccinelle from the current tip of https://github.com/coccinelle/coccinelle (1.0.7-00504-g670b2243). With my cut-down case, that version generates a diff with either semantic patch. But for the full-blown case in sequencer.c, it still only works with the angle brackets.

So my questions are:
  - is this a bug in coccinelle? Or I not understand how "..." is
    supposed to work here?
    (It does seem like there was possibly a separate bug introduced in
    1.0.6 that was later fixed; we can probably ignore that and just
    focus on the behavior in the current tip of master).
  - is there a better way to represent this kind of "transform this
    everywhere _except_ in this function" semantic patch? (preferably
    one that does not tickle this bug, if it is indeed a bug ;) ).
-Peff
Next: Julia Lawall
Message 1 of 4 in “excluding a function from coccinelle transformation”
  1. Jeff KingAug 24, 2018
  2. Julia LawallAug 24, 2018
  3. Jeff KingAug 24, 2018
  4. Julia LawallAug 24, 2018

Read the whole thread, see it on lore, or plain text.

$ cat FOOTERMessages come from the public archive at lore.kernel.org/git, fetched every hour. The front page is chosen and written each morning by an AI editor and can be wrong; the threads themselves are the record. About and API. For agents: an MCP server at https://gitlist.dev/mcp, and any thread, story or person page as Markdown by adding .md to its URL (or sending Accept: text/markdown). Details in /llms.txt.