[parted-devel] [PATCH 05/24] libparted: Avoid warnings from GCC 8 -Wsuggest-attribute=pure

[Brian C. Lane]

On Mon, Nov 16, 2020 at 03:39:58PM -0500, Phillip Susi wrote:
> 
> Brian C. Lane writes:
> 
> > From: Shin'ichiro Kawasaki <kawasaki at juno.dti.ne.jp>
> >
> > GCC 8 suggests to add 'pure' attribute to a number of functions but the
> > warnings might be false positive. The suggested functions have PED_ASSERT
> > macro which may call abort() function. One of the functions
> > fat_table_get() calls exit() function also. Once abort() or exit()
> 
> If that is true then we need to remove that exit() call.  As a library,
> libparted should not be calling exit().

I think we should wait until after this release. It's buried down in the
fat resize code and appears to be there because it doesn't have a good
way to indicate an error. It may require a change to the public API in
order to clean it up.

> 
> > called, the program execution stops. It is controversial if the functions
> > are pure or not, and consequence of compiler optimization with the pure
> > attribute is not explicit.
> 
> Doesn't "pure" mean that it does not modify any variables with static
> storage duration, so the caller can assume that any variables it has
> already loaded into registers that are preserved across the call do not
> need to be reloaded?  If so, then it should be perfectly safe to assume
> that abort() or exit() are pure.

I agree, the functions all only depend on what's passed to them for
their return value and the assert decision so behavior should be exactly
the same.

> > With this unclear situation, I suggest not to add _GL_ATTRIBUTE_PURE to
> > the functions. Instead, I suggest to avoid the warning message using GCC
> > pragma 'diagnostic ignored' pragma, which disables specific GCC warnings
> > only for target functions.
> 
> The pragma needs protected so that it is only used with gcc and not if
> you are using a different compiler that does not understand that pragma.

I dropped that patch and added pure to those functions so that no longer
matters.

Is anyone using llvm (or something else) to build parted? And is that
something that we really want to encourage? Seems simpler if we just say
'use gcc'.

Brian

-- 
Brian C. Lane (PST8PDT) - weldr.io - lorax - parted - pykickstart