From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>,
libc-alpha <libc-alpha@sourceware.org>,
Carlos O'Donell <carlos@redhat.com>,
Rich Felker <dalias@libc.org>,
linux-api <linux-api@vger.kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Will Deacon <will.deacon@arm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ben Maurer <bmaurer@fb.com>, Dave Watson <davejwatson@fb.com>,
Thomas Gleixner <tglx@linutronix.de>,
Paul <paulmck@linux.vnet.ibm.com>, Paul Turner <pjt@google.com>,
Joseph Myers <joseph@codesourcery.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>
Subject: Re: [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)
Date: Mon, 27 Apr 2020 16:27:37 -0400 (EDT) [thread overview]
Message-ID: <122741024.71528.1588019257574.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <2102127737.70791.1588008377292.JavaMail.zimbra@efficios.com>
----- On Apr 27, 2020, at 1:26 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
[...]
>>> We don't mind that user-space uses that pointer, but we never want the kernel
>>> to touch that pointer rather than the 32/64-bit-aware fields. One possibility
>>> would be to do:
>>>
>>> union
>>> {
>>> uint64_t ptr64;
>>> #ifdef __LP64__
>>> uint64_t ptr;
>>> #else
>>> struct
>>> {
>>> #if (defined (__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)) || defined
>>> (__BIG_ENDIAN)
>>> uint32_t padding; /* Initialized to zero. */
>>> uint32_t ptr32;
>>> #else /* LITTLE */
>>> uint32_t ptr32;
>>> uint32_t padding; /* Initialized to zero. */
>>> #endif /* ENDIAN */
>>> } ptr;
>>> #endif
>>>
>>> #ifndef __KERNEL__
>>> const struct rseq_cs *uptr;
>>> #endif
>>> } rseq_cs;
>>>
>>> in the union, so only user-space can see that field. Thoughts ?
>>
>> I think this depends on where the x32 question lands.
>
> x32 should not be an issue as explained above, so I'm very open to
> add this "uptr" for user-space only.
Actually, the snippet above is broken on 32-bit. It needs to be:
union
{
uint64_t ptr64;
#ifdef __LP64__
uint64_t ptr;
# ifndef __KERNEL__
const struct rseq_cs *uptr;
# endif
#else
struct
{
#if (defined (__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)) || defined (__BIG_ENDIAN)
uint32_t padding; /* Initialized to zero. */
uint32_t ptr32;
#else /* LITTLE */
uint32_t ptr32;
uint32_t padding; /* Initialized to zero. */
#endif /* ENDIAN */
} ptr;
# ifndef __KERNEL__
struct
{
# if (defined (__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)) || defined (__BIG_ENDIAN)
uint32_t padding; /* Initialized to zero. */
const struct rseq_cs *uptr32;
# else /* LITTLE */
const struct rseq_cs *uptr32;
uint32_t padding; /* Initialized to zero. */
# endif /* ENDIAN */
} uptr;
# endif
#endif
} rseq_cs;
I'll leave this out of the patchset for now as we'd need more feedback on its
usefulness.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2020-04-27 20:27 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200326155633.18236-1-mathieu.desnoyers@efficios.com>
2020-03-26 15:56 ` [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17) Mathieu Desnoyers
2020-04-27 9:11 ` Florian Weimer
2020-04-27 16:40 ` Mathieu Desnoyers
2020-04-27 16:54 ` Florian Weimer
2020-04-27 17:26 ` Mathieu Desnoyers
2020-04-27 20:27 ` Mathieu Desnoyers [this message]
2020-04-28 12:02 ` Florian Weimer
2020-04-28 12:33 ` Mathieu Desnoyers
2020-04-28 12:35 ` Florian Weimer
2020-04-28 12:43 ` Mathieu Desnoyers
2020-04-28 12:54 ` Florian Weimer
2020-04-28 14:58 ` Mathieu Desnoyers
2020-04-29 8:16 ` Szabolcs Nagy
2020-04-29 8:18 ` Florian Weimer
2020-04-29 8:52 ` Szabolcs Nagy
2020-04-28 12:56 ` Mathieu Desnoyers
2020-04-29 12:19 ` Florian Weimer
2020-04-27 11:59 ` Florian Weimer
2020-04-27 16:47 ` Mathieu Desnoyers
2020-04-27 16:59 ` Florian Weimer
2020-03-26 15:56 ` [PATCH glibc 6/9] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v7) Mathieu Desnoyers
2020-04-27 9:13 ` Florian Weimer
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