> -----Original Message----- > From: Guenter Roeck <groeck7@xxxxxxxxx> On Behalf Of Guenter Roeck > Sent: 13 September 2021 19:53 > To: Sam Ravnborg <sam@xxxxxxxxxxxx> > Cc: David S . Miller <davem@xxxxxxxxxxxxx>; sparclinux@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > Arnd Bergmann <arnd@xxxxxxxxxx> > Subject: Re: [PATCH] sparc: mdesc: Fix compile error seen with gcc 11.x > > On 9/13/21 11:02 AM, Sam Ravnborg wrote: > > Hi Guenter, > > > > On Mon, Sep 13, 2021 at 09:37:12AM -0700, Guenter Roeck 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@xxxxxxxxxx> > >> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> > >> --- > >> My apologies if a similar patch was submitted already; I was unable to find it. > >> I did find the following patch: > >> https://git.busybox.net/buildroot/commit/?id=6e1106b4a9aee25d1556310d5cd1cb6dde2e6e3f > >> but I failed to find it in patchwork or on lore.kernel.org, and it > >> seems to be more expensive than the solution suggested here. > >> > >> 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..c67bdcc23727 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[0]; > >> } __attribute__((aligned(16))); > > > > I do not think this will works. > > See following comment: > > * mdesc_hdr and mdesc_elem describe the layout of the data structure > > * we get from the Hypervisor. > > > > With the above change you increased the size from 16 to 32 bytes, > > and any code using sizeof(struct mdesc_hdr) will now point too far in > > memory for the second and subsequent entries. > > > > I did not take any closer look, but this was from a quick analysis. > > > > Sorry, I didn't realize that a field of size 0 increases the structure size > on sparc. I had checked the size of the old and the new structure with gcc > on x86_64 and didn't see a field size increase. clang output doesn't change: https://godbolt.org/z/bTeeq19j1 gcc ought to generate the same size. It ought to be 'char data[];' though. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
