On 5/19/2013 3:00 AM, rongqing.li@xxxxxxxxxxxxx wrote:
> From: "Roy.Li" <rongqing.li@xxxxxxxxxxxxx>
>
> On a number of arches, any fixed and shared mmap() mapping address must be
> aligned to 16k, or MIPS cpu askes that the address must be aligned to not
> violate cache aliasing constraints.
>
> If we create a shared memory like below:
>
> addr_orig = mmap (NULL, bytes, PROT_NONE,
> MAP_ANONYMOUS| MAP_PRIVATE, -1, 0);
>
> addr = mmap (addr_orig, bytes, PROT_READ | PROT_WRITE,
> MAP_FIXED | MAP_SHARED, fd, 0);
>
> If the first mmap() upper is not shared then the first mmap() will succeed
> because these restrictions do not apply to private mappings. The second
> mmap() wants a shared memory mapping but the address returned by the first
> one is only page-aligned and not aligned to 16k, or violate cache aliasing
> constraints on MIPS cpu, will lead to second mmap failure.
>
> Signed-off-by: Roy.Li <rongqing.li@xxxxxxxxxxxxx>
> ---
> configure.ac | 25 +++++++++++++++++++++++++
> exec/cpg.c | 13 +++++++++----
> lib/cpg.c | 10 ++++++++--
> 3 files changed, 42 insertions(+), 6 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index 523d2cf..d3a9c25 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -647,6 +647,31 @@ else
> AC_SUBST(VERSCRIPT_LDFLAGS, [""])
> fi
>
> +arch_force_shmlba=no
> +AC_MSG_CHECKING([for architecture in ${host_cpu}])
> +case $host_cpu in
> + sparc*)
> + AC_MSG_RESULT([${host_cpu}])
> + arch_force_shmlba=yes
> + ;;
> + arm*)
> + AC_MSG_RESULT([${host_cpu}])
> + arch_force_shmlba=yes
> + ;;
> + mips*)
> + AC_MSG_RESULT([${host_cpu}])
> + arch_force_shmlba=yes
> + ;;
> + *)
> + AC_MSG_RESULT([${host_cpu}])
> + ;;
> +esac
Hi,
this part of the patch is not ok. We spent a decent amount of time
dropping all hard coded architecture bits from configure.ac because they
are not portable.
You will need to find a more generic test to verify if shmlba is
necessary on a certain architecture/OS. Remember that we do support more
than just Linux for upstream.
Cheers
Fabio
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