* [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x
@ 2021-09-14 22:47 Guenter Roeck
2021-09-15 8:38 ` David Laight
2021-09-15 14:04 ` Arnd Bergmann
0 siblings, 2 replies; 3+ messages in thread
From: Guenter Roeck @ 2021-09-14 22:47 UTC (permalink / raw)
To: David S . Miller
Cc: sparclinux, linux-kernel, Guenter Roeck, Arnd Bergmann,
David Laight, Anatoly Pugachev, Sam Ravnborg
sparc64 images fail to compile with gcc 11.x, reporting the following
errors.
arch/sparc/kernel/mdesc.c:647:22: error:
'strcmp' reading 1 or more bytes from a region of size 0
arch/sparc/kernel/mdesc.c:692:22: error:
'strcmp' reading 1 or more bytes from a region of size 0
arch/sparc/kernel/mdesc.c:719:21:
error: 'strcmp' reading 1 or more bytes from a region of size 0
The underlying problem is that node_block() returns a pointer beyond
the end of struct mdesc_hdr. gcc 11.x detects that and reports the error.
Adding an additional zero-length field to struct mdesc_hdr and pointing
to that field fixes the problem.
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Anatoly Pugachev <matorola@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: data[0] => data[]
I am not sure if there was agreement to accept this patch or not, but
I was asked to resend it with the above change, so here it is. An open
question was if it is acceptable to have a structure named xxx_hdr
include an element pointing to the data following that header.
If this patch is not acceptable, the patch in buildbot may be a possible
alternative to consider.
https://git.busybox.net/buildroot/commit/?id=6e1106b4a9aee25d1556310d5cd1cb6dde2e6e3f
arch/sparc/kernel/mdesc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index 8e645ddac58e..83e1f699bc32 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -39,6 +39,7 @@ struct mdesc_hdr {
u32 node_sz; /* node block size */
u32 name_sz; /* name block size */
u32 data_sz; /* data block size */
+ char data[];
} __attribute__((aligned(16)));
struct mdesc_elem {
@@ -612,7 +613,7 @@ EXPORT_SYMBOL(mdesc_get_node_info);
static struct mdesc_elem *node_block(struct mdesc_hdr *mdesc)
{
- return (struct mdesc_elem *) (mdesc + 1);
+ return (struct mdesc_elem *) (mdesc->data);
}
static void *name_block(struct mdesc_hdr *mdesc)
--
2.33.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* RE: [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x
2021-09-14 22:47 [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x Guenter Roeck
@ 2021-09-15 8:38 ` David Laight
2021-09-15 14:04 ` Arnd Bergmann
1 sibling, 0 replies; 3+ messages in thread
From: David Laight @ 2021-09-15 8:38 UTC (permalink / raw)
To: 'Guenter Roeck', David S . Miller
Cc: sparclinux, linux-kernel, Arnd Bergmann, Anatoly Pugachev, Sam Ravnborg
From: Guenter Roeck
> Sent: 14 September 2021 23:47
...
> I am not sure if there was agreement to accept this patch or not, but
> I was asked to resend it with the above change, so here it is. An open
> question was if it is acceptable to have a structure named xxx_hdr
> include an element pointing to the data following that header.
It may be a pragmatic solution to the problem.
But it isn't 'correct'.
OTOH I think gcc is broken.
It ought to at least give a sane method of getting the warning
ignored in specific cases.
> If this patch is not acceptable, the patch in buildbot may be a possible
> alternative to consider.
> https://git.busybox.net/buildroot/commit/?id=6e1106b4a9aee25d1556310d5cd1cb6dde2e6e3f
>
> arch/sparc/kernel/mdesc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
> index 8e645ddac58e..83e1f699bc32 100644
> --- a/arch/sparc/kernel/mdesc.c
> +++ b/arch/sparc/kernel/mdesc.c
> @@ -39,6 +39,7 @@ struct mdesc_hdr {
> u32 node_sz; /* node block size */
> u32 name_sz; /* name block size */
> u32 data_sz; /* data block size */
> + char data[];
> } __attribute__((aligned(16)));
>
> struct mdesc_elem {
> @@ -612,7 +613,7 @@ EXPORT_SYMBOL(mdesc_get_node_info);
>
> static struct mdesc_elem *node_block(struct mdesc_hdr *mdesc)
> {
> - return (struct mdesc_elem *) (mdesc + 1);
> + return (struct mdesc_elem *) (mdesc->data);
> }
In order for gcc to consider (mdesc + 1) to have size 0
I think it must have tracked the pointer from a structure
that has another field (or structure end) following 'mdesc'.
If that is the case then it should also know that the data[]
must also be size 0.
So the warning may reappear with the next gcc version.
The busybox patch has:
+@@ -75,6 +75,7 @@ struct mdesc_handle {
+ refcount_t refcnt;
+ unsigned int handle_size;
+ struct mdesc_hdr mdesc;
++ char data[];
+ };
Which really ought to be more than enough.
Although the extra space could be considered to even be
outside that structure.
But the gcc folks suggested a completely brain-dead change
that requires taking the offset from the outer structure.
-- return (struct mdesc_elem *) (mdesc + 1);
++ return (struct mdesc_elem *) hp + offsetof(struct mdesc_handle, data);
which is probably missing a (char *) cast.
I wonder if it might be better to 'launder' the pointer
so that gcc can't track its size.
It may be that:
return (struct mdesc_elem *)(ulong)(mdesc + 1);
is enough.
Otherwise it will need to be passed into an asm block.
But gcc is getting stupid for system programming.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x
2021-09-14 22:47 [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x Guenter Roeck
2021-09-15 8:38 ` David Laight
@ 2021-09-15 14:04 ` Arnd Bergmann
1 sibling, 0 replies; 3+ messages in thread
From: Arnd Bergmann @ 2021-09-15 14:04 UTC (permalink / raw)
To: Guenter Roeck
Cc: David S . Miller, sparclinux, Linux Kernel Mailing List,
David Laight, Anatoly Pugachev, Sam Ravnborg
On Wed, Sep 15, 2021 at 12:47 AM Guenter Roeck <linux@roeck-us.net> wrote:
>
> sparc64 images fail to compile with gcc 11.x, reporting the following
> errors.
>
> arch/sparc/kernel/mdesc.c:647:22: error:
> 'strcmp' reading 1 or more bytes from a region of size 0
> arch/sparc/kernel/mdesc.c:692:22: error:
> 'strcmp' reading 1 or more bytes from a region of size 0
> arch/sparc/kernel/mdesc.c:719:21:
> error: 'strcmp' reading 1 or more bytes from a region of size 0
>
> The underlying problem is that node_block() returns a pointer beyond
> the end of struct mdesc_hdr. gcc 11.x detects that and reports the error.
> Adding an additional zero-length field to struct mdesc_hdr and pointing
> to that field fixes the problem.
>
> Cc: Arnd Bergmann <arnd@kernel.org>
> Cc: David Laight <David.Laight@ACULAB.COM>
> Cc: Anatoly Pugachev <matorola@gmail.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> v2: data[0] => data[]
>
> I am not sure if there was agreement to accept this patch or not, but
> I was asked to resend it with the above change, so here it is. An open
> question was if it is acceptable to have a structure named xxx_hdr
> include an element pointing to the data following that header.
>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-09-15 14:04 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-14 22:47 [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x Guenter Roeck
2021-09-15 8:38 ` David Laight
2021-09-15 14:04 ` Arnd Bergmann
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).