diff mbox series

kallsyms: work around bogus -Wrestrict warning

Message ID 20200107214042.855757-1-arnd@arndb.de (mailing list archive)
State New, archived
Headers show
Series kallsyms: work around bogus -Wrestrict warning | expand

Commit Message

Arnd Bergmann Jan. 7, 2020, 9:40 p.m. UTC
gcc -O3 produces some really odd warnings for this file:

kernel/kallsyms.c: In function 'sprint_symbol':
kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
   strcpy(buffer, name);
   ^~~~~~~~~~~~~~~~~~~~
kernel/kallsyms.c: In function 'sprint_symbol_no_offset':
kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
   strcpy(buffer, name);
   ^~~~~~~~~~~~~~~~~~~~
kernel/kallsyms.c: In function 'sprint_backtrace':
kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
   strcpy(buffer, name);
   ^~~~~~~~~~~~~~~~~~~~

This obviously cannot be since it is preceded by an 'if (name != buffer)'
check.

Using sprintf() instead of strcpy() is a bit wasteful but is
the best workaround I could come up with.

Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 kernel/kallsyms.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Andrew Morton Jan. 7, 2020, 10:25 p.m. UTC | #1
On Tue,  7 Jan 2020 22:40:26 +0100 Arnd Bergmann <arnd@arndb.de> wrote:

> gcc -O3 produces some really odd warnings for this file:
> 
> kernel/kallsyms.c: In function 'sprint_symbol':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> kernel/kallsyms.c: In function 'sprint_symbol_no_offset':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> kernel/kallsyms.c: In function 'sprint_backtrace':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> 
> This obviously cannot be since it is preceded by an 'if (name != buffer)'
> check.
> 
> Using sprintf() instead of strcpy() is a bit wasteful but is
> the best workaround I could come up with.
> 
> ...
>
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -366,7 +366,7 @@ static int __sprint_symbol(char *buffer, unsigned long address,
>  		return sprintf(buffer, "0x%lx", address - symbol_offset);
>  
>  	if (name != buffer)
> -		strcpy(buffer, name);
> +		sprintf(buffer, "%s", name);
>  	len = strlen(buffer);
>  	offset -= symbol_offset;

gee, is that even worth "fixing"?  Oleksandr, I've seen a couple of
these false positives.  Do we know if anyone is taking them to the gcc
developers?
Masami Hiramatsu Jan. 8, 2020, 1:26 a.m. UTC | #2
Hi Arnd,

On Tue,  7 Jan 2020 22:40:26 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> gcc -O3 produces some really odd warnings for this file:
> 
> kernel/kallsyms.c: In function 'sprint_symbol':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> kernel/kallsyms.c: In function 'sprint_symbol_no_offset':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> kernel/kallsyms.c: In function 'sprint_backtrace':
> kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
>    strcpy(buffer, name);
>    ^~~~~~~~~~~~~~~~~~~~
> 
> This obviously cannot be since it is preceded by an 'if (name != buffer)'
> check.

Hmm, this looks like a bug in gcc.

> 
> Using sprintf() instead of strcpy() is a bit wasteful but is
> the best workaround I could come up with.
> 
> Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  kernel/kallsyms.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index d812b90f4c86..726b8eeb223e 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -366,7 +366,7 @@ static int __sprint_symbol(char *buffer, unsigned long address,
>  		return sprintf(buffer, "0x%lx", address - symbol_offset);
>  
>  	if (name != buffer)
> -		strcpy(buffer, name);
> +		sprintf(buffer, "%s", name);

BTW, this seems not happen. kallsyms_lookup() (and it's subfunctions)
always stores the result into buffer unless name == NULL.
Maybe we can remove these 2 lines?
(and add a comment line for kallsyms_lookup() so that it guarantees the
 symbol name always stored in namebuf argument)

Thank you,
Oleksandr Natalenko Jan. 8, 2020, 9:23 a.m. UTC | #3
Hi.

On Tue, Jan 07, 2020 at 02:25:12PM -0800, Andrew Morton wrote:
> gee, is that even worth "fixing"?  Oleksandr, I've seen a couple of
> these false positives.  Do we know if anyone is taking them to the gcc
> developers?

I'm not aware of such an effort. I tend to blame compiler as an option
of last resort, but if Arnd gathers enough examples (since he's working
on fixing/working around those), it would be reasonable to suggest him to
hand over those findings to gcc bugtracker.
Andrew Morton Jan. 9, 2020, 10:02 p.m. UTC | #4
On Wed, 8 Jan 2020 10:26:02 +0900 Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Hi Arnd,
> 
> On Tue,  7 Jan 2020 22:40:26 +0100
> Arnd Bergmann <arnd@arndb.de> wrote:
> 
> > gcc -O3 produces some really odd warnings for this file:
> > 
> > kernel/kallsyms.c: In function 'sprint_symbol':
> > kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> >    strcpy(buffer, name);
> >    ^~~~~~~~~~~~~~~~~~~~
> > kernel/kallsyms.c: In function 'sprint_symbol_no_offset':
> > kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> >    strcpy(buffer, name);
> >    ^~~~~~~~~~~~~~~~~~~~
> > kernel/kallsyms.c: In function 'sprint_backtrace':
> > kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> >    strcpy(buffer, name);
> >    ^~~~~~~~~~~~~~~~~~~~
> > 
> > This obviously cannot be since it is preceded by an 'if (name != buffer)'
> > check.
> 
> Hmm, this looks like a bug in gcc.

Yes, we're getting a lot of such reports.  I don't think current gcc is
ready for this patch so I'll drop it, sorry.
Arnd Bergmann Jan. 9, 2020, 10:18 p.m. UTC | #5
On Thu, Jan 9, 2020 at 11:02 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed, 8 Jan 2020 10:26:02 +0900 Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > Hi Arnd,
> >
> > On Tue,  7 Jan 2020 22:40:26 +0100
> > Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > > gcc -O3 produces some really odd warnings for this file:
> > >
> > > kernel/kallsyms.c: In function 'sprint_symbol':
> > > kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> > >    strcpy(buffer, name);
> > >    ^~~~~~~~~~~~~~~~~~~~
> > > kernel/kallsyms.c: In function 'sprint_symbol_no_offset':
> > > kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> > >    strcpy(buffer, name);
> > >    ^~~~~~~~~~~~~~~~~~~~
> > > kernel/kallsyms.c: In function 'sprint_backtrace':
> > > kernel/kallsyms.c:369:3: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> > >    strcpy(buffer, name);
> > >    ^~~~~~~~~~~~~~~~~~~~
> > >
> > > This obviously cannot be since it is preceded by an 'if (name != buffer)'
> > > check.
> >
> > Hmm, this looks like a bug in gcc.
>
> Yes, we're getting a lot of such reports.  I don't think current gcc is
> ready for this patch so I'll drop it, sorry.

I've been building with gcc-8 and got around 20 false positive
warnings, three real bugs
and a few files that introduce increased stack usage. I have sent
patches for every one
of these and have a clean randconfig builds again on arm, arm64 and
x86 (a few thousand
so far).

Most of the false-positive warnings are for understandable reasons and easy to
work around, the one above is probably the most blatant screwup by gcc.

My feeling is that we can deal with the warnings here and I wouldn't
mind getting
it enabled in mainline from that perspective, but there are two caveats:

- v5.6 is probably too early since we're close to the merge window and a lot of
  my fixups have not been merged yet

- I have no good estimate of how many runtime failures there will be.
  Oleksandr hasn't found any issues after running with -O3 kernels for
  a longer time, but any significant change to the toolchain likely causes
  problems for somebody.

        Arnd
diff mbox series

Patch

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index d812b90f4c86..726b8eeb223e 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -366,7 +366,7 @@  static int __sprint_symbol(char *buffer, unsigned long address,
 		return sprintf(buffer, "0x%lx", address - symbol_offset);
 
 	if (name != buffer)
-		strcpy(buffer, name);
+		sprintf(buffer, "%s", name);
 	len = strlen(buffer);
 	offset -= symbol_offset;