Messages in this thread | | | From | "Gustavo A. R. Silva" <> | Subject | Re: [RFC PATCH] coccinelle: misc: add flexible_array.cocci script | Date | Fri, 7 Aug 2020 11:18:50 -0500 |
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Hi Denis,
Thanks a lot for working on this. Please, see some comments below...
On 8/6/20 17:03, Denis Efremov wrote: > Commit 68e4cd17e218 ("docs: deprecated.rst: Add zero-length and one-element > arrays") marks one-element and zero-length arrays as deprecated. Kernel > code should always use "flexible array members" instead. > > The script warns about one-element and zero-length arrays in structs. > > Cc: Kees Cook <keescook@chromium.org> > Cc: Gustavo A. R. Silva <gustavoars@kernel.org> > Signed-off-by: Denis Efremov <efremov@linux.com> > --- > > Currently, it's just a draft. I've placed a number of questions in the > script and marked them as TODO. Kees, Gustavo, if you could help me with > my questions I think that this rule will be enough to close: > https://github.com/KSPP/linux/issues/76 > > BTW, I it's possible to not warn about files in uapi folder if > this is relevant. Do I need to do it in the script? >
I think the script should warn about new additions of zero-length/one-element arrays in UAPI.
> scripts/coccinelle/misc/flexible_array.cocci | 158 +++++++++++++++++++ > 1 file changed, 158 insertions(+) > create mode 100644 scripts/coccinelle/misc/flexible_array.cocci > > diff --git a/scripts/coccinelle/misc/flexible_array.cocci b/scripts/coccinelle/misc/flexible_array.cocci > new file mode 100644 > index 000000000000..1e7165c79e60 > --- /dev/null > +++ b/scripts/coccinelle/misc/flexible_array.cocci > @@ -0,0 +1,158 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/// > +/// Zero-length and one-element arrays are deprecated, see > +/// Documentation/process/deprecated.rst > +/// Flexible-array members should be used instead. > +/// > +// > +// Confidence: High > +// Copyright: (C) 2020 Denis Efremov ISPRAS. > +// Comments: > +// Options: --no-includes --include-headers > + > +virtual context > +virtual report > +virtual org > +virtual patch > + > +@r depends on !patch@ > +identifier name, size, array; > +// TODO: We can additionally restrict size and array to: > +// identifier size =~ ".*(num|len|count|size|ncpus).*"; > +// identifier array !~ ".*(pad|reserved).*"; > +// Do we need it? > +type TS, TA; > +position p; > +@@ > + > +( > + // This will also match: typedef struct name { ... > + // However nested structs are not matched, i.e.: > + // struct name1 { struct name2 { int s; int a[0]; } st; int i; } > + // will not be matched. Do we need to handle it?
It's fine. I think this would be a different script. One that exclusively look for all three: zero-length, one-element arrays and flexible array members in nested structures because "A structure containing a flexible array member, or a union containing such a structure (possibly recursively), may not be a member of a structure or an element of an array. (However these uses are permitted by GCC as extensions.)"[1]
> + struct name { > + ... // TODO: Maybe simple ... is enough? It will match structs with a
Yep; simple is always better at first. :)
> + TS size; // single field, e.g. > + ... // https://elixir.bootlin.com/linux/v5.8/source/arch/arm/include/uapi/asm/setup.h#L127 > +( > +* TA array@p[0]; > +| > + // TODO: It seems that there are exception cases for array[1], e.g. > + // https://elixir.bootlin.com/linux/v5.8/source/arch/powerpc/boot/rs6000.h#L152 > + // https://elixir.bootlin.com/linux/v5.8/source/include/uapi/linux/cdrom.h#L292 > + // https://elixir.bootlin.com/linux/v5.8/source/drivers/net/wireless/ath/ath6kl/usb.c#L108 > + // We could either drop array[1] checking from this rule or > + // restrict array name with regexp and add, for example, an "allowlist" > + // with struct names where we allow this code pattern. > + // TODO: How to handle: u8 data[1][MAXLEN_PSTR6]; ? > +* TA array@p[1]; > +) > + }; > +| > + struct { > + ... > + TS size; > + ... > +( > +* TA array@p[0]; > +| > +* TA array@p[1]; > +) > + }; > +| > + // TODO: do we need to handle unions?
Yep; we should warn about this in unions, too.
However, I think unions cannot have members with incomplete type, so we should not suggest the use of flexible-array members in unions, because flexible arrays have incomplete type.
> + union name { > + ... > + TS size; > + ... > +( > +* TA array@p[0]; > +| > +* TA array@p[1]; > +) > + }; > +| > + union { > + ... > + TS size; > + ... > +( > +* TA array@p[0]; > +| > +* TA array@p[1]; > +) > + }; > +) > + > +// FIXME: Patch mode doesn't work as expected. > +// Coccinelle handles formatting incorrectly. > +// Patch mode in this rule should be disabled until > +// proper formatting will be supported. > +@depends on patch exists@ > +identifier name, size, array; > +type TS, TA; > +@@ > + > +( > + struct name { > + ... > + TS size; > + ... > +( > +- TA array[0]; > +| > +- TA array[1]; > +) > ++ TA array[]; > + }; > +| > + struct { > + ... > + TS size; > + ... > +( > +- TA array[0]; > +| > +- TA array[1]; > +) > ++ TA array[]; > + }; > +| > + union name { > + ... > + TS size; > + ... > +( > +- TA array[0]; > +| > +- TA array[1]; > +) > ++ TA array[]; > + }; > +| > + union { > + ... > + TS size; > + ... > +( > +- TA array[0]; > +| > +- TA array[1]; > +) > ++ TA array[];
This is not allowed, neither is GCC[2] nor in Clang[3].
> + }; > +) > + > +@script: python depends on report@ > +p << r.p; > +@@ > + > +msg = "WARNING: use flexible-array member instead" > +coccilib.report.print_report(p[0], msg) > + > +@script: python depends on org@ > +p << r.p; > +@@ > + > +msg = "WARNING: use flexible-array member instead" > +coccilib.org.print_todo(p, msg) >
I wonder if it might be worth it to also point people to the documentation in deprecated.rst (commit 68e4cd17e218 ("docs: deprecated.rst: Add zero-length and one-element arrays")), once helpdesk generates the official documentation for 5.9-rc1.
Thanks -- Gustavo
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://godbolt.org/z/Kajd7e [3] https://godbolt.org/z/dvKMYb
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