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Most of our semantic patches in 'contrib/coccinelle/object_id.cocci'
turn calls of SHA1-specific functions into calls of their
corresponding object_id counterparts, e.g. sha1_to_hex() to
oid_to_hex(). These semantic patches look something like this:
@@
expression E1;
@@
- sha1_to_hex(E1.hash)
+ oid_to_hex(&E1)
and match the access to the 'hash' field in any data type, not only in
'struct object_id', and, consquently, can produce wrong
transformations.
Case in point is the recent hash function transition patch "rerere:
convert to use the_hash_algo" [1], which, among other things, renamed
'struct rerere_dir's 'sha1' field to 'hash', and then 'make
coccicheck' started to suggest the following wrong transformations for
'rerere.c' [2]:
- return sha1_to_hex(id->collection->hash);
+ return oid_to_hex(id->collection);
and
- DIR *dir = opendir(git_path("rr-cache/%s", sha1_to_hex(rr_dir->hash)));
+ DIR *dir = opendir(git_path("rr-cache/%s", oid_to_hex(rr_dir)));
Avoid such wrong transformations by tightening semantic patches in
'object_id.cocci' to match only type of or pointers to 'struct
object_id'.
[1] https://public-inbox.org/git/20181008215701.779099-15-sandals@crustytoothpaste.net/
[2] https://travis-ci.org/git/git/jobs/440463476#L580
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This rounds out the previous three patches, covering the
inequality logic for the "hash" variant of the functions.
As with the previous three, the accompanying code changes
are the mechanical result of applying the coccinelle patch;
see those patches for more discussion.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This is the flip side of the previous two patches: checking
for a non-zero oidcmp() can be more strictly expressed as
inequality. Like those patches, we write "!= 0" in the
coccinelle transformation, which covers by isomorphism the
more common:
if (oidcmp(E1, E2))
As with the previous two patches, this patch can be achieved
almost entirely by running "make coccicheck"; the only
differences are manual line-wrap fixes to match the original
code.
There is one thing to note for anybody replicating this,
though: coccinelle 1.0.4 seems to miss the case in
builtin/tag.c, even though it's basically the same as all
the others. Running with 1.0.7 does catch this, so
presumably it's just a coccinelle bug that was fixed in the
interim.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This is the partner patch to the previous one, but covering
the "hash" variants instead of "oid". Note that our
coccinelle rule is slightly more complex to avoid triggering
the call in hasheq().
I didn't bother to add a new rule to convert:
- hasheq(E1->hash, E2->hash)
+ oideq(E1, E2)
Since these are new functions, there won't be any such
existing callers. And since most of the code is already
using oideq, we're not likely to introduce new ones.
We might still see "!hashcmp(E1->hash, E2->hash)" from topics
in flight. But because our new rule comes after the existing
ones, that should first get converted to "!oidcmp(E1, E2)"
and then to "oideq(E1, E2)".
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Using the more restrictive oideq() should, in the long run,
give the compiler more opportunities to optimize these
callsites. For now, this conversion should be a complete
noop with respect to the generated code.
The result is also perhaps a little more readable, as it
avoids the "zero is equal" idiom. Since it's so prevalent in
C, I think seasoned programmers tend not to even notice it
anymore, but it can sometimes make for awkward double
negations (e.g., we can drop a few !!oidcmp() instances
here).
This patch was generated almost entirely by the included
coccinelle patch. This mechanical conversion should be
completely safe, because we check explicitly for cases where
oidcmp() is compared to 0, which is what oideq() is doing
under the hood. Note that we don't have to catch "!oidcmp()"
separately; coccinelle's standard isomorphisms make sure the
two are treated equivalently.
I say "almost" because I did hand-edit the coccinelle output
to fix up a few style violations (it mostly keeps the
original formatting, but sometimes unwraps long lines).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Sometimes we want to suppress a coccinelle 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 that like this:
@@
identifier f != oidcmp;
expression E1, E2;
@@
f(...) {...
- hashcmp(E1->hash, E2->hash)
+ oidcmp(E1, E2)
...}
to match the interior of any function _except_ oidcmp().
Unfortunately, this doesn't catch all cases (e.g., the one
in sequencer.c that this patch fixes). The problem, as
explained by one of the Coccinelle developers in [1], is:
For transformation, A ... B requires that B occur on every
execution path starting with A, unless that execution path
ends up in error handling code. (eg, if (...) { ...
return; }). Here your A is the start of the function. So
you need a call to hashcmp on every path through the
function, which fails when you add ifs.
[...]
Another issue with A ... B is that by default A and B
should not appear in the matched region. So your original
rule matches only the case where every execution path
contains exactly one call to hashcmp, not more than one.
One way to solve this is to put the pattern inside an
angle-bracket pattern like "<... P ...>", which allows zero
or more matches of P. That works (and is what this patch
does), but it has one drawback: it matches more than we care
about, and Coccinelle uses extra CPU. Here are timings for
"make coccicheck" before and after this patch:
[before]
real 1m27.122s
user 7m34.451s
sys 0m37.330s
[after]
real 2m18.040s
user 10m58.310s
sys 0m41.549s
That's not ideal, but it's more important for this to be
correct than to be fast. And coccicheck is already fairly
slow (and people don't run it for every single patch). So
it's an acceptable tradeoff.
There _is_ a better way to do it, which is to record the
position at which we find hashcmp(), and then check it
against the forbidden function list. Like:
@@
position p : script:python() { p[0].current_element != "oidcmp" };
expression E1,E2;
@@
- hashcmp@p(E1->hash, E2->hash)
+ oidcmp(E1, E2)
This is only a little slower than the current code, and does
the right thing in all cases. Unfortunately, not all builds
of Coccinelle include python support (including the ones in
Debian). Requiring it may mean that fewer people can easily
run the tool, which is worse than it simply being a little
slower.
We may want to revisit this decision in the future if:
- builds with python become more common
- we find more uses for python support that tip the
cost-benefit analysis
But for now this patch sticks with the angle-bracket
solution, and converts all existing cocci patches. This
fixes only one missed case in the current code, though it
makes a much better difference for some new rules I'm adding
(converting "!hashcmp()" to "hasheq()" misses over half the
possible conversions using the old form).
[1] https://public-inbox.org/git/alpine.DEB.2.21.1808240652370.2344@hadrien/
Helped-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The object_id functions oid_to_hex, oid_to_hex_r, oidclr, oidcmp, and
oidcpy are defined as wrappers of their legacy counterparts sha1_to_hex,
sha1_to_hex_r, hashclr, hashcmp, and hashcpy, respectively. Make sure
that the Coccinelle transformations for converting legacy function calls
are not applied to these wrappers themselves, which would result in
tautological declarations.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Both sha1_to_hex_r() and oid_to_hex_r() take two parameters, so use two
expressions in the semantic patch for transforming calls of the former
to the latter one.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Coccinelle (http://coccinelle.lip6.fr/) is a program which performs
mechanical transformations on C programs using semantic patches. These
semantic patches can be used to implement automatic refactoring and
maintenance tasks.
Add a set of basic semantic patches to convert common patterns related
to the struct object_id transformation, as well as a README.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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SZEDER Gábor
Jeff King
René Scharfe
brian m. carlson