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

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Date:   Fri, 26 Aug 2016 13:58:03 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Michal Marek <mmarek@...e.cz>
Cc:     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 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;
 
 	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;
 		crc = (unsigned int) sym->st_value;
 		sym_update_crc(symname + strlen(CRC_PFX), mod, crc,
 				export);
@@ -663,6 +665,10 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
 		else
 			symname++;
 #endif
+		if (is_crc && !mod->is_dot_o) {
+			const char *e = is_vmlinux(mod->name) ?"":".ko";
+			warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n", symname + strlen(CRC_PFX), mod->name, e);
+		}
 		mod->unres = alloc_symbol(symname,
 					  ELF_ST_BIND(sym->st_info) == STB_WEAK,
 					  mod->unres);