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Re: [Qemu-devel] [PATCH] linux-user: Fix do_store_exclusive for shared m
From: |
Emilio G. Cota |
Subject: |
Re: [Qemu-devel] [PATCH] linux-user: Fix do_store_exclusive for shared memory of interprocess. |
Date: |
Sun, 16 Oct 2016 16:34:46 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
(Adding Richard to Cc)
On Sat, Oct 15, 2016 at 23:53:48 +0800, Heiher wrote:
> From: Heiher <address@hidden>
>
> test case: http://pastebin.com/raw/x2GW4xNW
You should check out this patchset and use it as a base for working on this
topic:
http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg02341.html
In particular, the added tests/atomic_add-bench does a very similar thing
to what you're doing with your test case -- although with pthreads instead of
mmap(MAP_SHARED) + fork.
(more comments below)
> Signed-off-by: Heiher <address@hidden>
> ---
> linux-user/main.c | 24 ++++++++++++++++++++++--
> 1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 0e31dad..81b0a49 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -2312,6 +2312,23 @@ static const uint8_t mips_syscall_args[] = {
> # undef MIPS_SYS
> # endif /* O32 */
>
> +#define cmpxchg_user(old, new, gaddr, target_type) \
> +({ \
> + abi_ulong __gaddr = (gaddr); \
> + target_type *__hptr; \
> + abi_long __ret = 0;
> \
> + if ((__hptr = lock_user(VERIFY_WRITE, __gaddr, sizeof(target_type), 0)))
> { \
> + if ((old) != atomic_cmpxchg(__hptr, (old), (new))) \
> + __ret = -TARGET_EAGAIN; \
> + unlock_user(__hptr, __gaddr, sizeof(target_type)); \
> + } else \
> + __ret = -TARGET_EFAULT;
> \
> + __ret; \
> +})
> +
> +#define cmpxchg_user_u32(old, new, gaddr) cmpxchg_user((old), (new),
> (gaddr), uint32_t)
> +#define cmpxchg_user_u64(old, new, gaddr) cmpxchg_user((old), (new),
> (gaddr), uint64_t)
> +
> static int do_store_exclusive(CPUMIPSState *env)
> {
> target_ulong addr;
> @@ -2342,12 +2359,15 @@ static int do_store_exclusive(CPUMIPSState *env)
> env->active_tc.gpr[reg] = 0;
> } else {
> if (d) {
> - segv = put_user_u64(env->llnewval, addr);
> + segv = cmpxchg_user_u64(env->llval, env->llnewval, addr);
> } else {
> - segv = put_user_u32(env->llnewval, addr);
> + segv = cmpxchg_user_u32(env->llval, env->llnewval, addr);
> }
> if (!segv) {
> env->active_tc.gpr[reg] = 1;
> + } else if (-TARGET_EAGAIN == segv) {
> + segv = 0;
> + env->active_tc.gpr[reg] = 0;
> }
> }
> }
With the atomic cmpxchg patch series referenced above, we should directly
translate to cmpxchg, thereby removing the exception--just like this
patch does for the Alpha architecture:
http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg02373.html
Thanks
Emilio