Messages in this thread | | | From | Guenter Roeck <> | Subject | Re: [PATCH] sparc: mdesc: Fix compile error seen with gcc 11.x | Date | Mon, 13 Sep 2021 11:52:52 -0700 |
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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@kernel.org> >> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >> --- >> 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; }
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