From: Vincent Chen <vincent.chen@sifive.com>
To: Rich Felker <dalias@libc.org>
Cc: Florian Weimer <fweimer@redhat.com>,
GNU C Library <libc-alpha@sourceware.org>,
Andrew Waterman <andrew@sifive.com>
Subject: Re: [RFC patch 2/5] RISC-V: Reserve about 5K space in mcontext_t to support future ISA expansion.
Date: Thu, 16 Sep 2021 16:02:50 +0800 [thread overview]
Message-ID: <CABvJ_xjGZ3S0oAkT08x4DToQFdcUH06omk2OTT1EHDZRJ-2wKg@mail.gmail.com> (raw)
In-Reply-To: <20210913135247.GL13220@brightrain.aerifal.cx>
On Mon, Sep 13, 2021 at 9:52 PM Rich Felker <dalias@libc.org> wrote:
>
> On Mon, Sep 13, 2021 at 03:44:09PM +0200, Florian Weimer via Libc-alpha wrote:
> > * Vincent Chen:
> >
> > > Following the changes of struct sigcontext in Linux to reserve about 5K space
> > > to support future ISA expansion.
> > > ---
> > > sysdeps/unix/sysv/linux/riscv/sys/ucontext.h | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/sysdeps/unix/sysv/linux/riscv/sys/ucontext.h b/sysdeps/unix/sysv/linux/riscv/sys/ucontext.h
> > > index cfafa44..80caf07 100644
> > > --- a/sysdeps/unix/sysv/linux/riscv/sys/ucontext.h
> > > +++ b/sysdeps/unix/sysv/linux/riscv/sys/ucontext.h
> > > @@ -82,6 +82,8 @@ typedef struct mcontext_t
> > > {
> > > __riscv_mc_gp_state __gregs;
> > > union __riscv_mc_fp_state __fpregs;
> > > + /* 5K + 256 reserved for vector state and future expansion. */
> > > + unsigned char __reserved[5376] __attribute__ ((__aligned__ (16)));
> > > } mcontext_t;
> >
Hi Florian and Rich,
Sorry for the late reply and thank you for reminding me the
modification will cause ABI break.
> > This changes the size of struct ucontext_t, which is an ABI break
> > (getcontext callers are supposed to provide their own object).
> >
The riscv vector registers are all caller-saved registers except for
VCSR. Therefore, the struct mcontext_t needs to reserve a space for
it. In addition, RISCV ISA is growing, so I also hope the struct
mcontext_t has a space for future expansion. Based on the above ideas,
I reserved a 5K space here.
> > This shouldn't be necessary if the additional vector registers are
> > caller-saved.
Here I am a little confused about the usage of struct mcontext_t. As
far as I know, the struct mcontext_t is used to save the
machine-specific information in user context operation. Therefore, in
this case, the struct mcontext_t is allowed to reserve the space only
for saving caller-saved registers. However, in the signal handler, the
user seems to be allowed to use uc_mcontext whose data type is struct
mcontext_t to access the content of the signal context. In this case,
the struct mcontext_t may need to be the same as the struct sigcontext
defined at kernel. However, it will have a conflict with your
suggestion because the struct sigcontext cannot just reserve a space
for saving caller-saved registers. Could you help me point out my
misunderstanding? Thank you.
> Indeed, that was my first thought when I saw this too. Any late
> additions to the register file must be call-clobbered or else they are
> a new ABI. And mcontext_t does not need to represent any
> call-clobbered state.
>
> Rich
next prev parent reply other threads:[~2021-09-16 8:03 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 1:41 [RFC patch 0/5] RISC-V: Add vector ISA support Vincent Chen
2021-09-13 1:41 ` [RFC patch 1/5] RISC-V: Remove riscv-specific sigcontext.h Vincent Chen
2021-09-13 1:41 ` [RFC patch 2/5] RISC-V: Reserve about 5K space in mcontext_t to support future ISA expansion Vincent Chen
2021-09-13 13:44 ` Florian Weimer via Libc-alpha
2021-09-13 13:52 ` Rich Felker
2021-09-16 8:02 ` Vincent Chen [this message]
2021-09-16 8:14 ` Florian Weimer via Libc-alpha
2021-09-18 3:04 ` Vincent Chen
2022-12-09 3:39 ` RISCV kernel struct sigcontext expansion for V regs and potential glibc ABI break (was Re: [RFC patch 2/5] RISC-V: Reserve about 5K space in mcontext_t to support future ISA expansion.) Vineet Gupta
2022-12-09 4:03 ` Vineet Gupta
2022-12-20 20:05 ` Adding V-ext regs to signal context w/o expanding kernel struct sigcontext to avoid glibc ABI break Vineet Gupta
2022-12-21 15:53 ` Vincent Chen
2022-12-21 19:45 ` Vineet Gupta
2022-12-21 19:52 ` Vineet Gupta
2022-12-22 3:37 ` Vincent Chen
2022-12-22 19:25 ` Vineet Gupta
2022-12-23 2:27 ` Vincent Chen
2022-12-23 19:42 ` Vineet Gupta
2022-12-22 5:32 ` Richard Henderson via Libc-alpha
2022-12-22 18:33 ` Andy Chiu
2022-12-22 20:27 ` Vineet Gupta
2022-12-28 10:53 ` Andy Chiu
2023-01-03 19:17 ` Vineet Gupta
2023-01-04 16:34 ` Andy Chiu
2023-01-04 20:46 ` Vineet Gupta
2023-01-04 21:29 ` Philipp Tomsich
2023-01-04 21:37 ` Andrew Waterman
2023-01-04 22:43 ` Vineet Gupta
2023-01-09 13:33 ` Kito Cheng
2023-01-09 19:16 ` Vineet Gupta
2023-01-10 13:21 ` Kito Cheng
2023-01-10 18:07 ` Auto-enabling V unit and/or use of elf attributes (was Re: Adding V-ext regs to signal context w/o expanding kernel struct sigcontext to avoid glibc ABI break) Vineet Gupta
2023-01-11 1:22 ` Richard Henderson via Libc-alpha
2023-01-11 4:28 ` Jeff Law
2023-01-11 4:57 ` Richard Henderson via Libc-alpha
2023-01-11 5:07 ` Jeff Law
2023-01-11 6:00 ` Andy Chiu
2023-01-11 6:20 ` Jeff Law
2023-01-11 9:28 ` Andy Chiu
2023-01-11 12:13 ` Andy Chiu
2023-01-23 12:17 ` Conor Dooley via Libc-alpha
2023-01-23 13:29 ` Andy Chiu
2023-01-11 5:05 ` Anup Patel
2023-01-11 5:23 ` Richard Henderson via Libc-alpha
2022-12-22 22:33 ` Adding V-ext regs to signal context w/o expanding kernel struct sigcontext to avoid glibc ABI break Richard Henderson via Libc-alpha
2022-12-22 23:47 ` Conor Dooley via Libc-alpha
2022-12-22 23:58 ` Vineet Gupta
2022-12-22 20:30 ` Vineet Gupta
2022-12-22 21:38 ` Andrew Waterman
2022-12-22 1:50 ` Vincent Chen
2022-12-22 5:34 ` Richard Henderson via Libc-alpha
2021-09-16 23:56 ` [RFC patch 2/5] RISC-V: Reserve about 5K space in mcontext_t to support future ISA expansion Ben Woodard via Libc-alpha
2021-09-18 3:15 ` Vincent Chen
2021-09-20 16:41 ` DJ Delorie via Libc-alpha
2021-09-20 17:10 ` Florian Weimer via Libc-alpha
2021-10-01 1:43 ` Vincent Chen
2021-10-01 12:08 ` Adhemerval Zanella via Libc-alpha
2021-09-17 17:03 ` Rich Felker
2021-09-18 3:19 ` Vincent Chen
2021-09-13 1:41 ` [RFC patch 3/5] RISC-V: Save and restore VCSR when doing user context switch Vincent Chen
2021-09-14 23:48 ` Joseph Myers
2021-09-15 0:13 ` Andrew Waterman
2021-09-16 9:20 ` Vincent Chen
2021-10-01 13:04 ` Adhemerval Zanella via Libc-alpha
2021-09-13 1:41 ` [RFC patch 4/5] RISC-V: Extend MINSIGSTKSZ and SIGSTKSZ to backup RVV registers Vincent Chen
2021-09-13 13:51 ` Rich Felker
2021-09-16 9:25 ` Vincent Chen
2021-09-13 1:41 ` [RFC 5/5] RISC-V: Expand PTHREAD_STACK_MIN to support RVV environment Vincent Chen
2021-09-14 23:43 ` Joseph Myers
2021-09-15 10:42 ` Florian Weimer via Libc-alpha
2021-09-15 14:31 ` H.J. Lu via Libc-alpha
2021-09-16 10:21 ` Vincent Chen
2021-09-13 19:11 ` [RFC patch 0/5] RISC-V: Add vector ISA support Vineet Gupta via Libc-alpha
2021-09-15 19:37 ` Jim Wilson
2021-11-09 19:21 ` Darius Rad
2021-11-09 19:30 ` Andrew Waterman
2021-11-09 22:03 ` Darius Rad
2021-11-09 22:18 ` Andrew Waterman
2021-11-10 11:39 ` Darius Rad
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