linux-kernel - Re: linux-next: build warnings after merge of the kbuild tree

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Date:   Fri, 26 Aug 2016 06:21:27 +0000
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Michal Marek <mmarek@...e.cz>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-next@...r.kernel.org,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        linux-kbuild@...r.kernel.org
Subject: Re: linux-next: build warnings after merge of the kbuild tree

On Fri, Aug 26, 2016 at 01:58:03PM +1000, Nicholas Piggin wrote:
> On Mon, 22 Aug 2016 20:47:58 +1000
> Nicholas Piggin <npiggin@...il.com> wrote:
> 
> > On Fri, 19 Aug 2016 20:44:55 +1000
> > Nicholas Piggin <npiggin@...il.com> wrote:
> > 
> > > On Fri, 19 Aug 2016 10:37:00 +0200
> > > Michal Marek <mmarek@...e.cz> wrote:
> > >   
> > > > On 2016-08-19 07:09, Stephen Rothwell wrote:    
> > 
> > [snip]
> > 
> > > > > 
> > > > > I may be missing something, but genksyms generates the crc's off the
> > > > > preprocessed C source code and we don't have any for the asm files ...      
> > > > 
> > > > Of course you are right. Which means that we are losing type information
> > > > for these exports for CONFIG_MODVERSIONS purposes. I guess it's
> > > > acceptable, since the asm functions are pretty basic and their
> > > > signatures do not change.    
> > > 
> > > I don't completely agree. It would be nice to have the functionality
> > > still there.
> > > 
> > > What happens if you just run cmd_modversions on the as rule? It relies on
> > > !defined(__ASSEMBLY__), but we're feeding the result to genksyms, not as.
> > > It would require the header be included in the .S file and be protected for
> > > asm builds.  
> > 
> > 
> > This seems like it *could* be made to work, but there's a few problems.
> > 
> > - .h files are not made for C consumption. Matter of manually adding the
> > ifdef guards, which isn't terrible.
> > 
> > - .S files do not all include their .h where the C declaration is. Also
> > will cause some churn but doable and maybe not completely unreasonable.
> > 
> > - genksyms parser barfs when it hits the assembly of the .S file. Best
> > way to fix that seems just send the #include and EXPORT_SYMBOL lines
> > from the .S to the preprocessor. That's a bit of a rabbit hole too, with
> > some .S files being included, etc.
> > 
> > I'm not sure what to do here. If nobody cares and we lose CRCs for .S
> > exports, then okay we can whitelist those relocs easily. If we don't want
> > to lose the functionality, the above might work but it's a bit intrusive
> > an is going to require another cycle of prep patches to go through arch
> > code first.
> > 
> > Or suggestions for alternative approach?
> 
> Here is a quick patch that I think should catch missing CRCs in
> architecture independent way. If we merge something like this, we
> can whitelist the symbols in arch/powerpc so people get steered to
> the right place.
> 
> Powerpc seems to be the only one really catching this, and it's
> only as a side effect of a test run for CONFIG_RELOCATABLE kernels,
> which means version failures probably slipped through other archs.
> 
> I'll clean it up, do some more testing, and submit it unless
> anybody dislikes it or has a better way to do it.
> 
> Thanks,
> Nick
> 
> 
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 4b8ffd3..1efc454 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -609,6 +609,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
>  {
>  	unsigned int crc;
>  	enum export export;
> +	int is_crc = 0;

should that not be a bool here ?

>  
>  	if ((!is_vmlinux(mod->name) || mod->is_dot_o) &&
>  	    strncmp(symname, "__ksymtab", 9) == 0)
> @@ -618,6 +619,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
>  
>  	/* CRC'd symbol */
>  	if (strncmp(symname, CRC_PFX, strlen(CRC_PFX)) == 0) {
> +		is_crc = 1;

is_crc = true;

>  		crc = (unsigned int) sym->st_value;
>  		sym_update_crc(symname + strlen(CRC_PFX), mod, crc,
>  				export);

thx!
hofrat