[PATCH] promisor-remote: fix xcalloc() argument order

[PATCH] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

Pass the number of elements first and their size second, as expected
by xcalloc().

Patch generated with 'contrib/coccinelle/xcalloc.cocci' and Coccinelle
v1.0.7 or later (previous Coccinelle versions don't notice this).

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 promisor-remote.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/promisor-remote.c b/promisor-remote.c
index 5b33f88bca..68f46f5ec7 100644
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -146,7 +146,7 @@ static void promisor_remote_init(struct repository *r)
 	if (r->promisor_remote_config)
 		return;
 	config = r->promisor_remote_config =
-		xcalloc(sizeof(*r->promisor_remote_config), 1);
+		xcalloc(1, sizeof(*r->promisor_remote_config));
 	config->promisors_tail = &config->promisors;
 
 	repo_config(r, promisor_remote_config, config);
-- 
2.37.2.880.g3b8fb2ce68

Re: [PATCH] promisor-remote: fix xcalloc() argument order

[Junio C Hamano]

SZEDER Gábor <szeder.dev@gmail.com> writes:

> Pass the number of elements first and their size second, as expected
> by xcalloc().
>
> Patch generated with 'contrib/coccinelle/xcalloc.cocci' and Coccinelle
> v1.0.7 or later (previous Coccinelle versions don't notice this).

One thing is that Coccinelle is way too slow on our codebase,
compared to the usual compilation, to run every time we make
changes.  Combined with the fact that our codebase is mostly clean,
the cycles feel huge waste of time only to find something small like
what this patch fixes.

That sadly discourages us from doing "make coccicheck" more often as
we should.

I _think_ Googlers have 1.1.1 on their linux boxes, so even if our
GitHub Actions CI is fixed to Ubuntu 18.04 and does not run more
recent Coccinelle, we theoretically should have been able to catch
it before it hit the public list, if "1.0.7 or later" was the
condition.  FWIW, "make coccicheck" with what I happen to have
notices it.

$ spatch version
spatch version 1.1.1 compiled with OCaml version 4.13.1
Flags passed to the configure script: --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib --enable-ocaml --enable-python --enable-opt
OCaml scripting support: yes
Python scripting support: yes
Syntax of regular expressions: PCRE

Anyway, the patch is correct.

Thanks, will queue.

> Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
> ---
>  promisor-remote.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/promisor-remote.c b/promisor-remote.c
> index 5b33f88bca..68f46f5ec7 100644
> --- a/promisor-remote.c
> +++ b/promisor-remote.c
> @@ -146,7 +146,7 @@ static void promisor_remote_init(struct repository *r)
>  	if (r->promisor_remote_config)
>  		return;
>  	config = r->promisor_remote_config =
> -		xcalloc(sizeof(*r->promisor_remote_config), 1);
> +		xcalloc(1, sizeof(*r->promisor_remote_config));
>  	config->promisors_tail = &config->promisors;
>  
>  	repo_config(r, promisor_remote_config, config);

Re: [PATCH] promisor-remote: fix xcalloc() argument order

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> ...  FWIW, "make coccicheck" with what I happen to have
> notices it.

Oops, that was a serious typo.  "notices" -> "fails to notice".

> $ spatch version
> spatch version 1.1.1 compiled with OCaml version 4.13.1
> Flags passed to the configure script: --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib --enable-ocaml --enable-python --enable-opt
> OCaml scripting support: yes
> Python scripting support: yes
> Syntax of regular expressions: PCRE
>
> Anyway, the patch is correct.
>
> Thanks, will queue.
>
>> Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
>> ---
>>  promisor-remote.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/promisor-remote.c b/promisor-remote.c
>> index 5b33f88bca..68f46f5ec7 100644
>> --- a/promisor-remote.c
>> +++ b/promisor-remote.c
>> @@ -146,7 +146,7 @@ static void promisor_remote_init(struct repository *r)
>>  	if (r->promisor_remote_config)
>>  		return;
>>  	config = r->promisor_remote_config =
>> -		xcalloc(sizeof(*r->promisor_remote_config), 1);
>> +		xcalloc(1, sizeof(*r->promisor_remote_config));
>>  	config->promisors_tail = &config->promisors;
>>  
>>  	repo_config(r, promisor_remote_config, config);

Re: [PATCH] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

On Mon, Aug 22, 2022 at 06:09:41PM -0700, Junio C Hamano wrote:
> Junio C Hamano <gitster@pobox.com> writes:
> 
> > ...  FWIW, "make coccicheck" with what I happen to have
> > notices it.
> 
> Oops, that was a serious typo.  "notices" -> "fails to notice".

Hm, that's strange.  1.1.1 did notice this transformation for me, as
did 1.1.0, 1.0.8, 1.0.7, and, contrary to what I wrote in the commit
message, even 1.0.6 as well.  (IIRC Ubuntu 18.04 has 1.0.4, which I
didn't try, but if that could notice it, then we should have heard
about it from CI.)

$ spatch --version
spatch version 1.1.1 compiled with OCaml version 4.08.1
Flags passed to the configure script: [none]
OCaml scripting support: yes
Python scripting support: yes
Syntax of regular expressions: PCRE


> > $ spatch version
> > spatch version 1.1.1 compiled with OCaml version 4.13.1
> > Flags passed to the configure script: --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib --enable-ocaml --enable-python --enable-opt
> > OCaml scripting support: yes
> > Python scripting support: yes
> > Syntax of regular expressions: PCRE

Re: [PATCH] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

On Tue, Aug 23, 2022 at 09:04:17AM +0200, SZEDER Gábor wrote:
> On Mon, Aug 22, 2022 at 06:09:41PM -0700, Junio C Hamano wrote:
> > Junio C Hamano <gitster@pobox.com> writes:
> > 
> > > ...  FWIW, "make coccicheck" with what I happen to have
> > > notices it.
> > 
> > Oops, that was a serious typo.  "notices" -> "fails to notice".
> 
> Hm, that's strange.  1.1.1 did notice this transformation for me,

Hang on, it's not quite that simple.
Watch this, it will get weird:

# Batched spatch for faster processing, see 960154b9c1 (coccicheck:
# optionally batch spatch invocations, 2019-05-06)
$ grep SPATCH_BATCH_SIZE config.mak
SPATCH_BATCH_SIZE = 32
$ time make contrib/coccinelle/xcalloc.cocci.patch    
    SPATCH contrib/coccinelle/xcalloc.cocci
     SPATCH result: contrib/coccinelle/xcalloc.cocci.patch

real	0m35.902s
user	0m34.840s
sys	0m1.030s
# Found it, good.
$ make -s cocciclean
# Turn off batched processing (this is the default)
$ sed -i -e '/SPATCH_BATCH_SIZE/ s/= .*/= 1/' config.mak
$ time make contrib/coccinelle/xcalloc.cocci.patch    
    SPATCH contrib/coccinelle/xcalloc.cocci

real	0m24.553s
user	0m21.468s
sys	0m3.099s
# Not only missed the transformation, but it's faster than batched
# processing?!

# Let's invoke spatch directly.
$ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c                               
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c
# Nope.
$ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c lockfile.c
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c lockfile.c
$ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c git.c     
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c git.c
$ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c usage.c
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c usage.c
# Nope, nope, nope.
$ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c builtin/*.c
[...]
# Nope!

# But watch this!
$ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c config.c
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c config.c
diff = 
diff -u -p a/promisor-remote.c b/promisor-remote.c
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -146,7 +146,7 @@ static void promisor_remote_init(struct
 	if (r->promisor_remote_config)
 		return;
 	config = r->promisor_remote_config =
-		xcalloc(sizeof(*r->promisor_remote_config), 1);
+		xcalloc(1, sizeof(*r->promisor_remote_config));
 	config->promisors_tail = &config->promisors;
 
 	repo_config(r, promisor_remote_config, config);

# Huh?! (;

FWIW, I see this with Coccinelle 1.1.1, 1.0.8 and 1.0.6 as well.

Re: [PATCH] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

On Tue, Aug 23, 2022 at 11:21:56AM +0200, SZEDER Gábor wrote:
> On Tue, Aug 23, 2022 at 09:04:17AM +0200, SZEDER Gábor wrote:
> > On Mon, Aug 22, 2022 at 06:09:41PM -0700, Junio C Hamano wrote:
> > > Junio C Hamano <gitster@pobox.com> writes:
> > > 
> > > > ...  FWIW, "make coccicheck" with what I happen to have
> > > > notices it.
> > > 
> > > Oops, that was a serious typo.  "notices" -> "fails to notice".
> > 
> > Hm, that's strange.  1.1.1 did notice this transformation for me,


> # Let's invoke spatch directly.
> $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c                               
> warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
> warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
> HANDLING: promisor-remote.c
> # Nope.
> $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c lockfile.c
> warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
> warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
> HANDLING: promisor-remote.c lockfile.c
> $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c git.c     
> warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
> warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
> HANDLING: promisor-remote.c git.c
> $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c usage.c
> warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
> warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
> HANDLING: promisor-remote.c usage.c
> # Nope, nope, nope.
> $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c builtin/*.c
> [...]
> # Nope!
> 
> # But watch this!
> $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c config.c
> warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
> warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
> HANDLING: promisor-remote.c config.c
> diff = 
> diff -u -p a/promisor-remote.c b/promisor-remote.c
> --- a/promisor-remote.c
> +++ b/promisor-remote.c
> @@ -146,7 +146,7 @@ static void promisor_remote_init(struct
>  	if (r->promisor_remote_config)
>  		return;
>  	config = r->promisor_remote_config =
> -		xcalloc(sizeof(*r->promisor_remote_config), 1);
> +		xcalloc(1, sizeof(*r->promisor_remote_config));
>  	config->promisors_tail = &config->promisors;
>  
>  	repo_config(r, promisor_remote_config, config);
> 
> # Huh?! (;
> 
> FWIW, I see this with Coccinelle 1.1.1, 1.0.8 and 1.0.6 as well.

Ok, I think I got this.

The transformation involves 'r->promisor_remote_config', where 'r' is
a 'struct repository*'.  However, 'promisor-remote.c' doesn't include
'repository.h' directly:

  $ grep '^#include' promisor-remote.c 
  #include "cache.h"
  #include "object-store.h"
  #include "promisor-remote.h"
  #include "config.h"
  #include "transport.h"
  #include "strvec.h"

If I add an '#include "repository.h" to 'promisor-remote.c', then
Coccinelle finds the transformation even when it processes this source
file on is own:

  $ spatch --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c
  init_defs_builtins: /usr/local/lib/coccinelle/standard.h
  HANDLING: promisor-remote.c
  diff = 
  diff -u -p a/promisor-remote.c b/promisor-remote.c
  --- a/promisor-remote.c
  +++ b/promisor-remote.c
  @@ -149,7 +149,7 @@ static void promisor_remote_init(struct
   	if (r->promisor_remote_config)
   		return;
   	config = r->promisor_remote_config =
  -		xcalloc(sizeof(*r->promisor_remote_config), 1);
  +		xcalloc(1, sizeof(*r->promisor_remote_config));
   	config->promisors_tail = &config->promisors;
   
   	repo_config(r, promisor_remote_config, config);

[PATCH v2] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

Pass the number of elements first and their size second, as expected
by xcalloc().

Patch generated with:

  make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch

Our default SPATCH_FLAGS ('--all-includes') doesn't catch this
transformation by default, unless used in combination with a large-ish
SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file
that includes 'repository.h' directly in the same batch.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 promisor-remote.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/promisor-remote.c b/promisor-remote.c
index 5b33f88bca..68f46f5ec7 100644
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -146,7 +146,7 @@ static void promisor_remote_init(struct repository *r)
 	if (r->promisor_remote_config)
 		return;
 	config = r->promisor_remote_config =
-		xcalloc(sizeof(*r->promisor_remote_config), 1);
+		xcalloc(1, sizeof(*r->promisor_remote_config));
 	config->promisors_tail = &config->promisors;
 
 	repo_config(r, promisor_remote_config, config);
-- 
2.37.2.880.g3b8fb2ce68

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[Jeff King]

On Tue, Aug 23, 2022 at 11:57:33AM +0200, SZEDER Gábor wrote:

> Pass the number of elements first and their size second, as expected
> by xcalloc().
> 
> Patch generated with:
> 
>   make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch

Thanks for digging here. I think it probably explains a lot of "wait,
why did this result change" head-scratching I did back when we started
batching a few years ago.

Is there any reason we wouldn't want --recursive-includes to be added to
the default SPATCH_FLAGS?

I suspect we'd still want to leave --all-includes there to get as much
type information as possible. If I understand correctly, the two are
orthogonal (one is "follow includes of includes" and the other is
"follow system includes in angle brackets").

Doing so doesn't seem to find any other missed entries in the current
codebase, but I'm pretty sure there are some it would have caught in a
less mysterious fashion over the years.

-Peff

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

On Wed, Aug 24, 2022 at 04:32:41AM -0400, Jeff King wrote:
> On Tue, Aug 23, 2022 at 11:57:33AM +0200, SZEDER Gábor wrote:
> 
> > Pass the number of elements first and their size second, as expected
> > by xcalloc().
> > 
> > Patch generated with:
> > 
> >   make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch
> 
> Thanks for digging here. I think it probably explains a lot of "wait,
> why did this result change" head-scratching I did back when we started
> batching a few years ago.
> 
> Is there any reason we wouldn't want --recursive-includes to be added to
> the default SPATCH_FLAGS?

I ran some runtime measurements yesterday, and there is a considerable
runtime increase in the unbatched case:

    The tables below show the runtimes of applying each of our semantic
    patches separately with Coccinelle v1.1.1, with the '--all-includes'
    or '--recursive-includes' flags and with batch sizes 1 (no batching)
    or 32, i.e.:
    
      time make SPATCH_FLAGS=$flag SPATCH_BATCH_SIZE=$size $cocci.patch
    
    SPATCH_BATCH_SIZE=1:
    
       semantic patch  |    all    | recursive |
      -----------------+-----------+-----------+--------
       array           |   69.90s  |  140.12s  |  +100%
       commit          |   94.44s  |  223.63s  |  +137%
       equals-null     |   86.93s  |  205.40s  |  +136%
       flex_alloc      |   11.32s  |   16.45s  |   +45%
       free            |   70.47s  |  159.75s  |  +127%
       hashmap         |   83.48s  |  199.70s  |  +139%
       object_id       |  107.83s  |  241.69s  |  +124%
       preincr         |   79.33s  |  202.98s  |  +156%
       qsort           |   16.20s  |   33.86s  |  +109%
       strbuf          |   60.54s  |  129.93s  |  +115%
       swap            |   81.70s  |  200.75s  |  +146%
       unused          |  499.19s  |  626.35s  |   +25%
       xcalloc         |   26.71s  |   57.63s  |  +116%
       xopen           |   30.92s  |   59.26s  |   +92%
       xstrdup_or_null |    5.05s  |    6.94s  |   +37%
      -----------------+-----------+-----------+--------
       all             |    1324s  |    2504s  |   +89%
    
    SPATCH_BATCH_SIZE=32:
    
       semantic patch  |    all    | recursive |
      -----------------+-----------+-----------+--------
       array           |   43.81s  |   52.83s  |   +21%
       commit          |   50.16s  |   52.76s  |    +5%
       equals-null     |   47.77s  |   50.86s  |    +6%
       flex_alloc      |   41.00s  |   43.64s  |    +6%
       free            |   43.12s  |   46.68s  |    +8%
       hashmap         |   42.76s  |   46.12s  |    +8%
       object_id       |   56.17s  |   60.00s  |    +7%
       preincr         |   39.82s  |   42.57s  |    +7%
       qsort           |   39.48s  |   53.09s  |   +34%
       strbuf          |   51.27s  |   49.38s  |    -4%
       swap            |   41.93s  |   58.17s  |   +39%
       unused          |  440.86s  |  445.47s  |    +1%
       xcalloc         |   39.90s  |   42.22s  |    +6%
       xopen           |   40.26s  |   43.19s  |    +7%
       xstrdup_or_null |   39.14s  |   41.72s  |    +7%
      -----------------+-----------+-----------+--------
       all             |    1057s  |    1129s  |    +7%
    
    I don't have meaningful numbers about the impact of
    '--recursive-includes' on the runtime of a parallel 'make -j<N>
    coccicheck', because they're severely skewed by 'unused.cocci' and
    'make's scheduler: applying 'unused.cocci' takes 5-10x as long as
    other semantic patches (accounting for about 38-42% of the total
    sequential runtime), and 'make' on my system usually schedules it near
    the end, meaning that for a significant part there is no parallel
    processing at all.

So I'm not sure about making '--recursive-includes' the default, at
least as long as we don't batch by default.  However, we could still
use this flag in CI...

> I suspect we'd still want to leave --all-includes there to get as much
> type information as possible. If I understand correctly, the two are
> orthogonal (one is "follow includes of includes" and the other is
> "follow system includes in angle brackets").

'spatch --help' tells me:

  --recursive-includes    causes all available include files, both
                          those included in the C file(s) and those
                          included in header files, to be used
  --all-includes          causes all available include files included
                          in the C file(s) to be used

So I think the difference is not about system includes, but rather
about "consider includes of includes" vs. "consider only direct
includes in the C files", so it seems '--recursive-includes' is a
superset of '--all-includes'.  Oh, and let's not forget the rather
surprising behavior that if spatch processes multiple C files at once,
then for each of the C files it considers all includes from all C
files; this explains why '--all-includes promisor-remote.c config.c'
works, because 'config.c' does include 'repository.h', supplying the
necessary type information to catch the previously missed
transformation in 'promisor-remote.c'.


These descriptions don't make it clear (to me) whether the two options
are orthogonal, exclusive, or something else.  However, trying out various
combinations indicates that "last one wins", e.g.:

$ spatch --recursive-includes --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c
$ spatch --all-includes --recursive-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c
warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h
warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso
HANDLING: promisor-remote.c
diff = 
diff -u -p a/promisor-remote.c b/promisor-remote.c
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -146,7 +146,7 @@ static void promisor_remote_init(struct
 	if (r->promisor_remote_config)
 		return;
 	config = r->promisor_remote_config =
-		xcalloc(sizeof(*r->promisor_remote_config), 1);
+		xcalloc(1, sizeof(*r->promisor_remote_config));
 	config->promisors_tail = &config->promisors;
 
 	repo_config(r, promisor_remote_config, config);

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[Junio C Hamano]

SZEDER Gábor <szeder.dev@gmail.com> writes:

> Patch generated with:
>
>   make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch
>
> Our default SPATCH_FLAGS ('--all-includes') doesn't catch this
> transformation by default, unless used in combination with a large-ish
> SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file
> that includes 'repository.h' directly in the same batch.

Our default SPATCH_FLAGS is actually

    SPATCH_FLAGS = --all-includes --patch .

and I am wondering how "--patch ." part (or droppage thereof due to
overriding it from the command line) affects the outcome.

In any case, good finding how the header file inclusion was affected
with batch-size and this option that solved a mystery.  Thanks.

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[SZEDER Gábor]

On Wed, Aug 24, 2022 at 08:58:21AM -0700, Junio C Hamano wrote:
> SZEDER Gábor <szeder.dev@gmail.com> writes:
> 
> > Patch generated with:
> >
> >   make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch
> >
> > Our default SPATCH_FLAGS ('--all-includes') doesn't catch this
> > transformation by default, unless used in combination with a large-ish
> > SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file
> > that includes 'repository.h' directly in the same batch.
> 
> Our default SPATCH_FLAGS is actually
> 
>     SPATCH_FLAGS = --all-includes --patch .
> 
> and I am wondering how "--patch ." part (or droppage thereof due to
> overriding it from the command line) affects the outcome.

'--patch .' is not part of SPATCH_FLAGS anymore, and for a good
reason, see the recent 7b63ea5750 (Makefile: remove mandatory "spatch"
arguments from SPATCH_FLAGS, 2022-07-05).

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[Junio C Hamano]

SZEDER Gábor <szeder.dev@gmail.com> writes:

> On Wed, Aug 24, 2022 at 08:58:21AM -0700, Junio C Hamano wrote:
>> SZEDER Gábor <szeder.dev@gmail.com> writes:
>> 
>> > Patch generated with:
>> >
>> >   make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch
>> >
>> > Our default SPATCH_FLAGS ('--all-includes') doesn't catch this
>> > transformation by default, unless used in combination with a large-ish
>> > SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file
>> > that includes 'repository.h' directly in the same batch.
>> 
>> Our default SPATCH_FLAGS is actually
>> 
>>     SPATCH_FLAGS = --all-includes --patch .
>> 
>> and I am wondering how "--patch ." part (or droppage thereof due to
>> overriding it from the command line) affects the outcome.
>
> '--patch .' is not part of SPATCH_FLAGS anymore, and for a good
> reason, see the recent 7b63ea5750 (Makefile: remove mandatory "spatch"
> arguments from SPATCH_FLAGS, 2022-07-05).

Ahh, that makes my life a bit more cumbersome, as I was looking at
how we did things on the 'maint' branch.

Thanks, mystery solved.

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[Jeff King]

On Wed, Aug 24, 2022 at 01:39:01PM +0200, SZEDER Gábor wrote:

> I ran some runtime measurements yesterday, and there is a considerable
> runtime increase in the unbatched case:

Let me condense and rearrange this a bit to the part I think is
important:

>        semantic patch  |    all    | recursive |
>       -----------------+-----------+-----------+--------
>     SPATCH_BATCH_SIZE=1:
>        all             |    1324s  |    2504s  |   +89%
>     SPATCH_BATCH_SIZE=32:
>        all             |    1057s  |    1129s  |    +7%

Right, that's not surprising. "recursive" means we're looking at more
header files than before. For the batch case it has less impact because
it's more likely that some other file we're processing in the batch
_also_ was looking at that header, so we saw it anyway.

With an infinite bath size, adding --recursive-includes should make no
difference (or almost none; it's possible there are headers which
are _only_ included recursively across the whole code base).

My numbers for array.cocci are:

  SPATCH_BATCH_SIZE=1,  133s
  SPATCH_BATCH_SIZE=32,  34s
  SPATCH_BATCH_SIZE=0,   31s

Of course there we run into potential memory problems. Based on glancing
at top occasionally, the first one peaked around 100MB of memory, the
second around 200MB, and the third one around 2GB. So "32" is probably
still a reasonable middle ground for CPU vs memory.

Spending extra CPU, especially for people stuck BATCH_SIZE=1, does suck.
But the tool is already terribly slow. Even if we spend twice as much
CPU (which is what your numbers above show), isn't it worth it to get
the _correct_ result? To me there is not much point in running it at all
if it misses cases.

It would be nice if there was some way to tell coccinelle not to
actually _analyze_ included header files, but just to include them to
pick up types, etc (and then we'd add the headers themselves to
COCCI_SOURCES to check them). But I don't see a way to do that. And I
wouldn't be surprised if the code simply isn't written in a way to make
that easy internally.

Another alternative would be --no-includes (and again, listing the
headers manually via COCCI_SOURCES). But as the example you found shows,
it really does need the headers in order to properly process the code in
the C files themselves.

>     I don't have meaningful numbers about the impact of
>     '--recursive-includes' on the runtime of a parallel 'make -j<N>
>     coccicheck', because they're severely skewed by 'unused.cocci' and
>     'make's scheduler: applying 'unused.cocci' takes 5-10x as long as
>     other semantic patches (accounting for about 38-42% of the total
>     sequential runtime), and 'make' on my system usually schedules it near
>     the end, meaning that for a significant part there is no parallel
>     processing at all.

It may be that unused.cocci can be optimized. Once upon a time I spent
some effort optimizing some of the rules files. I found that if you
relied on having python support, it helped quite a bit, because without
it you are stuck with the "..." operator, which can be very expensive.
More details in this thread:

  https://lore.kernel.org/git/20180824064228.GA3183@sigill.intra.peff.net/

Back then the debian package wasn't being actively updated, and it
wasn't clear if python support would remain. But these days it seems a
bit more stable.  And with the CI job available, I'd prefer to optimize
over making the tool pleasant to use for people who do use it, rather
than worrying that everybody on every platform/build can use it.

All that said, I am not about to get sucked into the rabbit hole of
coccinelle optimization anytime soon. So good luck to you, if you're
interested. ;)

> > I suspect we'd still want to leave --all-includes there to get as much
> > type information as possible. If I understand correctly, the two are
> > orthogonal (one is "follow includes of includes" and the other is
> > "follow system includes in angle brackets").
> 
> 'spatch --help' tells me:
> 
>   --recursive-includes    causes all available include files, both
>                           those included in the C file(s) and those
>                           included in header files, to be used
>   --all-includes          causes all available include files included
>                           in the C file(s) to be used
> 
> So I think the difference is not about system includes, but rather
> about "consider includes of includes" vs. "consider only direct
> includes in the C files", so it seems '--recursive-includes' is a
> superset of '--all-includes'.

I'm not sure, because there's also --local-includes and --no-includes,
which are grouped with --all-includes. (The grouping is doubly confusing
because my copy of the manpage has _two_ options sections, and only some
of the options are mentioned together in the first one).

> Oh, and let's not forget the rather surprising behavior that if spatch
> processes multiple C files at once, then for each of the C files it
> considers all includes from all C files; this explains why
> '--all-includes promisor-remote.c config.c' works, because 'config.c'
> does include 'repository.h', supplying the necessary type information
> to catch the previously missed transformation in 'promisor-remote.c'.

Right. I have a feeling it is sucking in as much data as possible to a
global symbol table, and then doing the analysis. At least that's how
I'd implement it. ;)

> These descriptions don't make it clear (to me) whether the two options
> are orthogonal, exclusive, or something else.  However, trying out various
> combinations indicates that "last one wins", e.g.:

OK, that's compelling evidence. In that case it wouldn't hurt to say:

  --all-includes --recursive-includes

versus just

  --recursive-includes

but it also probably isn't doing anything. ;)

-Peff

Re: [PATCH v2] promisor-remote: fix xcalloc() argument order

[Ævar Arnfjörð Bjarmason]

On Wed, Aug 24 2022, Jeff King wrote:

> On Tue, Aug 23, 2022 at 11:57:33AM +0200, SZEDER Gábor wrote:
>
>> Pass the number of elements first and their size second, as expected
>> by xcalloc().
>> 
>> Patch generated with:
>> 
>>   make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch
>
> Thanks for digging here. I think it probably explains a lot of "wait,
> why did this result change" head-scratching I did back when we started
> batching a few years ago.
>
> Is there any reason we wouldn't want --recursive-includes to be added to
> the default SPATCH_FLAGS?
>
> I suspect we'd still want to leave --all-includes there to get as much
> type information as possible. If I understand correctly, the two are
> orthogonal (one is "follow includes of includes" and the other is
> "follow system includes in angle brackets").
>
> Doing so doesn't seem to find any other missed entries in the current
> codebase, but I'm pretty sure there are some it would have caught in a
> less mysterious fashion over the years.

This feels to me like hacks around other issues we should fix the root
cause of.

So, first of all, I think this is a perfectly good fix, and something we
should do more of in general. It'll apply the wanted change *and* speed
up the run:
	
	diff --git a/contrib/coccinelle/xcalloc.cocci b/contrib/coccinelle/xcalloc.cocci
	index c291011607e..bd51e33af83 100644
	--- a/contrib/coccinelle/xcalloc.cocci
	+++ b/contrib/coccinelle/xcalloc.cocci
	@@ -1,10 +1,8 @@
	 @@
	-type T;
	-T *ptr;
	 expression n;
	 @@
	   xcalloc(
	 + n,
	-  \( sizeof(T) \| sizeof(*ptr) \)
	+  sizeof(...)
	 - , n
	   )

But it's *not* functionally the same thing, pedantically speaking, but I
think it's fine. I pointed this out at the the time in [1].

Also, more generally we could avoid includes in headers, and use forward
decls. This would make e.g. the "iwyu" tool report the missing include.

Unfortunately it seems we added it in this case due to
"the_repository". I wonder if this hack would be better:

	diff --git a/Makefile b/Makefile
	index 9410a587fc0..92d5726b392 100644
	--- a/Makefile
	+++ b/Makefile
	@@ -3119,6 +3119,7 @@ HCC = $(HCO:hco=hcc)
	 
	 %.hcc: %.h
	 	@echo '#include "git-compat-util.h"' >$@
	+	@echo "extern struct repository *the_repository;" >>$@
	 	@echo '#include "$<"' >>$@
	 
	 $(HCO): %.hco: %.hcc FORCE
	diff --git a/promisor-remote.h b/promisor-remote.h
	index edc45ab0f5f..e864c093a44 100644
	--- a/promisor-remote.h
	+++ b/promisor-remote.h
	@@ -1,7 +1,7 @@
	 #ifndef PROMISOR_REMOTE_H
	 #define PROMISOR_REMOTE_H
	 
	-#include "repository.h"
	+struct repository;
	 
	 struct object_id;
	 
	@@ -23,6 +23,7 @@ static inline void promisor_remote_reinit(void)
	 	repo_promisor_remote_reinit(the_repository);
	 }
	 
	+struct promisor_remote_config;
	 void promisor_remote_clear(struct promisor_remote_config *config);
	 
	 struct promisor_remote *repo_promisor_remote_find(struct repository *r, const char *remote_name);

So yeah, one way to deal with this is --recursive-includes, but I think
we're better off heading in the direction of having the includes for a
given *.c file be what it actually needs, and not rely on includes by
proxy, or in this case to pollute the namespace of everyone using
promisor-remote.h with remote.h (probably doesn't matter in that case,
but in the general case...).

1. https://lore.kernel.org/git/87ft18tcog.fsf@evledraar.gmail.com/