On Tue, Sep 14, 2021 at 3:54 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > 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. > > Guenter > > --- > Test code I had used: > > #include <stddef.h> > #include <stdio.h> > > typedef unsigned int u32; > > struct mdesc_hdr { > u32 version; /* Transport version */ > u32 node_sz; /* node block size */ > u32 name_sz; /* name block size */ > u32 data_sz; /* data block size */ > } __attribute__((aligned(16))); > > struct mdesc_hdr2 { > u32 version; /* Transport version */ > u32 node_sz; /* node block size */ > u32 name_sz; /* name block size */ > u32 data_sz; /* data block size */ > char data[0]; > } __attribute__((aligned(16))); > > int main() > { > printf("%ld %ld\n", sizeof(struct mdesc_hdr), sizeof(struct mdesc_hdr2)); > > return 0; > } used the code above on my sparc64 installation: copy-paste code to 123.c file $ gcc-11 123.c $ ./a.out 16 16 $ uname -a Linux ttip 5.15.0-rc1 #273 SMP Mon Sep 13 12:47:14 MSK 2021 sparc64 GNU/Linux
