On 07.01.25 20:49, Mats Kindahl wrote:
This is the first example semantic patch and shows how to capture and
fix a common problem.
If you use an palloc() to allocate memory for an object (or an array of
objects) and by mistake type something like:
StringInfoData *info = palloc(sizeof(StringInfoData*));
You will not allocate enough memory for storing the object. This
semantic patch catches any cases where you are either allocating an
array of objects or a single object that do not have corret types in
this sense, more precisely, it captures assignments to a variable of
type T* where palloc() uses sizeof(T) either alone or with a single
expression (assuming this is an array count).
The semantic patch is overzealous in the sense that allocation to a
"const char **" expects a "sizeof(const char *)" and it cannot deal with
typedefs that introduce aliases (these two can be seen in the patch).
Although the sizes of these are the same, and Coccinelle do not have a
good system for comparing types, it might be better to just follow the
convention of always using the type "T*" for any "palloc(sizeof(T))"
since it makes automated checking easier and is a small inconvenience;
especially considering that coccicheck can easily fix this for you. It
also simplifies other automated checking to follow this convention.
I think this kind of thing is better addressed with a static analyzer or
some heavier compiler annotations and warnings or something like that.
That kind of tool would have the right level of information to decide
whether some code is correct. Having a text matching tool do it is just
never going to be complete, and the problems you mention show that this
tool fundamentally doesn't understand the code, and just knows how to
parse the code a little better than grep or sed.
I do like the idea of exploring this tool for facilitating code
rewriting or semantic patching. But I'm suspicious about using it for
enforcing coding styles or patterns.
