Re: [Bug 221820] New: sparc64 mmap() returns EINVAL for non-MAP_FIXED hint within VA_EXCLUDE_START...END

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On Sat, 01 Aug 2026 09:41:47 +0000 [email protected] wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=221820
> 
>             Bug ID: 221820
>            Summary: sparc64 mmap() returns EINVAL for non-MAP_FIXED hint
>                     within VA_EXCLUDE_START...END
>            Product: Memory Management
>            Version: 2.5
>           Hardware: Sparc64
>                 OS: Linux
>             Status: NEW
>           Severity: normal
>           Priority: P3
>          Component: Other
>           Assignee: [email protected]
>           Reporter: [email protected]
>         Regression: No
> 
> Repro:
> 
>     alexrp@niagara:~$ uname -a
>     Linux niagara 7.1.3.1-sparc64-smp #1 SMP Debian 7.1.3-1+sunvdc (2026-07-12)
> sparc64 GNU/Linux
>     alexrp@niagara:~$ cat bug.c
>     #include <errno.h>
>     #include <stdio.h>
>     #include <string.h>
>     #include <sys/mman.h>
>     #include <unistd.h>
>     int main() {
>         long pgsz = sysconf(_SC_PAGE_SIZE);
>         void *addr = mmap((void *)0xfff80000fffc6000, pgsz, PROT_READ |
> PROT_WRITE, \
>           MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>         printf("%p (%s)\n", addr, strerror(errno));
>     }
>     alexrp@niagara:~$ cc bug.c
>     alexrp@niagara:~$ ./a.out
>     0xffffffffffffffff (Invalid argument)
> 
> I find this fairly surprising. I could understand if I had specified MAP_FIXED
> because in that case the kernel is unable to satisfy the requirements I've
> specified. But without MAP_FIXED, 0xfff80000fffc6000 is merely a hint and
> should be ignored if it falls within a VA range that the kernel considers
> off-limits.

Thanks.

That does seem wrong.  It works for me on x86_64 so yes, it does appear
to be a sparc thing.

The test code does have a few glitches which I don't think matter here, but below
is chatgpt's fixed-up version.  Could someone in sparcland please take a quick
look?

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

int main(void)
{
    long pgsz = sysconf(_SC_PAGE_SIZE);

    void *addr = mmap((void *)0xfff80000fffc6000,
                      pgsz,
                      PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANONYMOUS,
                      -1,
                      0);

    if (addr == MAP_FAILED) {
        fprintf(stderr, "mmap failed: %s\n", strerror(errno));
        return 1;
    }

    printf("mapped at %p\n", addr);

    munmap(addr, pgsz);
    return 0;
}