linux-kernel - Re: [PATCH RESEND 0/2] RISC-V: Handle the siginfo

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Message-ID: <CAK8P3a2NmdoHzFGKrzw4CBYDOBtZHDQCGsWE_L0UbG+w0bGWkA@mail.gmail.com>
Date:   Thu, 4 Jul 2019 11:19:13 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andreas Schwab <schwab@...e.de>
Cc:     Alistair Francis <alistair23@...il.com>,
        Alistair Francis <alistair.francis@....com>,
        linux-riscv@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND 0/2] RISC-V: Handle the siginfo_t offset problem

On Thu, Jul 4, 2019 at 9:20 AM Andreas Schwab <schwab@...e.de> wrote:
>
> On Jul 03 2019, Alistair Francis <alistair23@...il.com> wrote:
>
> > On Wed, Jul 3, 2019 at 12:08 AM Andreas Schwab <schwab@...e.de> wrote:
> >>
> >> On Jul 02 2019, Alistair Francis <alistair.francis@....com> wrote:
> >>
> >> > In the RISC-V 32-bit glibc port [1] the siginfo_t struct in the kernel
> >> > doesn't line up with the struct in glibc. In glibc world the _sifields
> >> > union is 8 byte alligned (although I can't figure out why)
> >>
> >> Try ptype/o in gdb.
> >
> > That's a useful tip, I'll be sure to use that next time.
>
> It was a serious note.  If the structs don't line up then there is a
> mismatch in types that cannot be solved by adding spurious padding.  You
> need to fix the types instead.

Would it be an option to align all the basic typedefs (off_t, time_t,
clock_t, ...)
between glibc and kernel then, and just use the existing
sysdeps/unix/sysv/linux/generic/bits/typesizes.h after all to avoid
surprises like this?

As of v2 the functional difference is

-#define __INO_T_TYPE        __ULONGWORD_TYPE
+#define __INO_T_TYPE    __UQUAD_TYPE
 #define __INO64_T_TYPE        __UQUAD_TYPE
 #define __MODE_T_TYPE        __U32_TYPE
-#define __NLINK_T_TYPE        __U32_TYPE
-#define __OFF_T_TYPE        __SLONGWORD_TYPE
+#define __NLINK_T_TYPE    __UQUAD_TYPE
+#define __OFF_T_TYPE    __SQUAD_TYPE
 #define __OFF64_T_TYPE        __SQUAD_TYPE
-#define __RLIM_T_TYPE        __ULONGWORD_TYPE
+#define __RLIM_T_TYPE      __UQUAD_TYPE
 #define __RLIM64_T_TYPE        __UQUAD_TYPE
-#define    __BLKCNT_T_TYPE        __SLONGWORD_TYPE
+#define __BLKCNT_T_TYPE    __SQUAD_TYPE
 #define    __BLKCNT64_T_TYPE    __SQUAD_TYPE
-#define    __FSBLKCNT_T_TYPE    __ULONGWORD_TYPE
+#define __FSBLKCNT_T_TYPE  __UQUAD_TYPE
 #define    __FSBLKCNT64_T_TYPE    __UQUAD_TYPE
-#define    __FSFILCNT_T_TYPE    __ULONGWORD_TYPE
+#define __FSFILCNT_T_TYPE  __UQUAD_TYPE
 #define    __FSFILCNT64_T_TYPE    __UQUAD_TYPE
-#define    __FSWORD_T_TYPE        __SWORD_TYPE
+#define __FSWORD_T_TYPE   __SQUAD_TYPE
-#define __CLOCK_T_TYPE        __SLONGWORD_TYPE
-#define __TIME_T_TYPE        __SLONGWORD_TYPE
+#define __CLOCK_T_TYPE     __SQUAD_TYPE
+#define __TIME_T_TYPE      __SQUAD_TYPE
 #define __USECONDS_T_TYPE    __U32_TYPE
-#define __SUSECONDS_T_TYPE    __SLONGWORD_TYPE
+#define __SUSECONDS_T_TYPE __SQUAD_TYPE
-#define __BLKSIZE_T_TYPE    __S32_TYPE
+#define __BLKSIZE_T_TYPE   __SQUAD_TYPE
 #define __FSID_T_TYPE        struct { int __val[2]; }
 #define __SSIZE_T_TYPE        __SWORD_TYPE
-#define __SYSCALL_SLONG_TYPE    __SLONGWORD_TYPE
-#define __SYSCALL_ULONG_TYPE    __ULONGWORD_TYPE
-#define __CPU_MASK_TYPE     __ULONGWORD_TYPE
+#define __SYSCALL_SLONG_TYPE __SQUAD_TYPE
+#define __SYSCALL_ULONG_TYPE __UQUAD_TYPE
+#define __CPU_MASK_TYPE    __UQUAD_TYPE

-#ifdef __LP64__
 # define __RLIM_T_MATCHES_RLIM64_T    1
-#else
-# define __RLIM_T_MATCHES_RLIM64_T    0
-#endif

+#define __ASSUME_TIME64_SYSCALLS 1
+#define __ASSUME_RLIM64_SYSCALLS 1

Since the sysdeps/unix/sysv/linux/generic/bits/typesizes.h definitions
generally match the kernel, anything diverging from that has the potential
of breaking it, so the difference should probably be kept to the absolute
minimum.

I think these ones are wrong and will cause bugs similar to the clock_t
issue if they are used with kernel interfaces:
__NLINK_T_TYPE, __FSWORD_T_TYPE, __CLOCK_T_TYPE,
__BLKSIZE_T_TYPE, __SYSCALL_ULONG_TYPE,
__SYSCALL_SLONG_TYPE, __CPU_MASK_TYPE

These are fine as long as they are only used in user space and to
wrap kernel syscalls, but I think most of them can end up being
passed to the kernel, so it seems safer not to have rv32 diverge
without a good reason.

The remaining ones (__INO_T_TYPE, __OFF_T_TYPE, __BLKCNT_T_TYPE,
__FSBLKCNT_T_TYPE, __FSFILCNT_T_TYPE, __TIME_T_TYPE) all
follow the pattern where the kernel has an old 32-bit type and a new
64-bit type, but the kernel tries not to expose the 32-bit interfaces
to user space on new architectures and only provide the 64-bit
replacements, but there are a couple of interfaces that never got
replaced, typically in driver and file system ioctls.

Since glibc already has code to deal with the 64-bit types and that
is well tested, it would seem safer to me to just #undef the old
types completely rather than defining them to 64-bit, which would
make them incompatible with the kernel's types.

       Arnd