[RFC] cacheflush.2: Document different prototypes for different architectures

Fri Dec 11 23:52:18 GMT 2020

On 12/11/20 10:09 PM, Alejandro Colomar (man-pages) wrote:
> Hi Michael,
>
> Continuing with the changes in this thread:
> https://lore.kernel.org/linux-man/747d56e0-c102-ab40-add4-530a48a43a4d@gmx.de/T/#t
>
> I researched the architectures that have this syscall.  I found some
> that clearly provide the syscall, and some that seem to have something,
> but I didn't find a definition in the kernel (i.e., ARM, MicroBlaze
> (glibc only)?)

arch/arm/include/uapi/asm/unistd.h:35:
#define __ARM_NR_cacheflush               (__ARM_NR_BASE+2)

arch/arm64/include/asm/unistd.h:37:
#define __ARM_NR_compat_cacheflush   (__ARM_NR_COMPAT_BASE + 2)

These syscalls are marked as private. So you should not use them from
user space.

The compilers seem not to care about these syscalls being private:

https://github.com/gcc-mirror/gcc/blob/master/libgcc/config/arm/lib1funcs.S#L1512
https://github.com/llvm-mirror/compiler-rt/blob/master/lib/builtins/clear_cache.c

Best regards

Heinrich

>
> Research:
>
> $ grep -rn cacheflush glibc/
> glibc/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist:324:GLIBC_2.0
> cacheflush F
> glibc/sysdeps/unix/sysv/linux/m68k/Versions:13:    cacheflush;
> glibc/sysdeps/unix/sysv/linux/m68k/arch-syscall.h:17:#define
> __NR_cacheflush 123
> glibc/sysdeps/unix/sysv/linux/m68k/syscalls.list:18:cacheflush	EXTRA
> cacheflush	i:iiii	__cacheflush	cacheflush
> glibc/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist:744:GLIBC_2.4
> cacheflush F
> glibc/sysdeps/unix/sysv/linux/arc/Versions:10:    cacheflush;
> glibc/sysdeps/unix/sysv/linux/arc/sys/cachectl.h:1:/* cacheflush - flush
> contents of instruction and/or data cache.
> glibc/sysdeps/unix/sysv/linux/arc/sys/cachectl.h:30:extern int
> cacheflush (void *__addr, int __nbytes, int __op) __THROW;
> glibc/sysdeps/unix/sysv/linux/arc/arch-syscall.h:13:#define
> __NR_cacheflush 244
> glibc/sysdeps/unix/sysv/linux/arc/syscalls.list:3:cacheflush	-
> cacheflush	i:pii	_flush_cache	cacheflush
> glibc/sysdeps/unix/sysv/linux/arc/Makefile:10:# MIPS/Tile-style
> cacheflush routine
> glibc/sysdeps/unix/sysv/linux/arc/Makefile:12:sysdep_routines += cacheflush
> glibc/sysdeps/unix/sysv/linux/arc/libc.abilist:574:GLIBC_2.32 cacheflush F
> glibc/sysdeps/unix/sysv/linux/csky/Versions:3:    cacheflush;
> glibc/sysdeps/unix/sysv/linux/csky/sys/cachectl.h:30:extern int
> cacheflush (void *__addr, const int __nbytes,
> glibc/sysdeps/unix/sysv/linux/csky/arch-syscall.h:10:#define
> __NR_cacheflush 245
> glibc/sysdeps/unix/sysv/linux/csky/syscalls.list:2:cacheflush	-
> cacheflush	i:pii	_flush_cache	cacheflush
> glibc/sysdeps/unix/sysv/linux/csky/Makefile:2:sysdep_routines += cacheflush
> glibc/sysdeps/unix/sysv/linux/csky/libc.abilist:594:GLIBC_2.29 cacheflush F
> glibc/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist:322:GLIBC_2.0
> cacheflush F
> glibc/sysdeps/unix/sysv/linux/mips/mips32/arch-syscall.h:19:#define
> __NR_cacheflush 4147
> glibc/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist:322:GLIBC_2.0
> cacheflush F
> glibc/sysdeps/unix/sysv/linux/mips/Versions:19:    cachectl; cacheflush;
> glibc/sysdeps/unix/sysv/linux/mips/sys/cachectl.h:35:extern int
> cacheflush (void *__addr, const int __nbytes, const int __op) __THROW;
> glibc/sysdeps/unix/sysv/linux/mips/mips64/n64/arch-syscall.h:16:#define
> __NR_cacheflush 5197
> glibc/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist:320:GLIBC_2.0
> cacheflush F
> glibc/sysdeps/unix/sysv/linux/mips/mips64/n32/arch-syscall.h:16:#define
> __NR_cacheflush 6197
> glibc/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist:322:GLIBC_2.0
> cacheflush F
> glibc/sysdeps/unix/sysv/linux/mips/syscalls.list:8:cacheflush	-
> cacheflush	i:pii	_flush_cache	cacheflush
> glibc/sysdeps/unix/sysv/linux/mips/Makefile:6:sysdep_routines +=
> cachectl cacheflush sysmips _test_and_set
> glibc/sysdeps/unix/sysv/linux/sh/arch-syscall.h:16:#define
> __NR_cacheflush 123
> glibc/sysdeps/unix/sysv/linux/nios2/Versions:4:    cacheflush;
> glibc/sysdeps/unix/sysv/linux/nios2/sys/cachectl.h:1:/* cacheflush -
> flush contents of instruction and/or data cache.
> glibc/sysdeps/unix/sysv/linux/nios2/sys/cachectl.h:27:extern int
> cacheflush (void *__addr, const int __nbytes, const int __op) __THROW;
> glibc/sysdeps/unix/sysv/linux/nios2/arch-syscall.h:10:#define
> __NR_cacheflush 244
> glibc/sysdeps/unix/sysv/linux/nios2/cacheflush.c:1:/* cacheflush system
> call for Nios II Linux.
> glibc/sysdeps/unix/sysv/linux/nios2/cacheflush.c:27:  return
> INLINE_SYSCALL (cacheflush, 3, addr, nbytes, op);
> glibc/sysdeps/unix/sysv/linux/nios2/cacheflush.c:29:weak_alias
> (_flush_cache, cacheflush)
> glibc/sysdeps/unix/sysv/linux/nios2/Makefile:6:# MIPS-style cacheflush
> routine
> glibc/sysdeps/unix/sysv/linux/nios2/Makefile:8:sysdep_routines += cacheflush
> glibc/sysdeps/unix/sysv/linux/nios2/libc.abilist:663:GLIBC_2.21 cacheflush F
> glibc/sysdeps/unix/sysv/linux/arm/dl-machine.h:23:
> INTERNAL_SYSCALL_CALL (cacheflush, (BEG), (END), 0)
> glibc/sysdeps/unix/sysv/linux/arm/arch-syscall.h:17:#define
> __NR_cacheflush 983042
> glibc/sysdeps/unix/sysv/linux/arm/fixup-asm-unistd.h:19:#ifndef
> __NR_cacheflush
> glibc/sysdeps/unix/sysv/linux/arm/fixup-asm-unistd.h:20:# define
> __NR_cacheflush __ARM_NR_cacheflush
> glibc/sysdeps/unix/sysv/linux/microblaze/syscalls.list:3:cacheflush
> EXTRA	cacheflush	i:iiii	__cacheflush	cacheflush
> glibc/sysdeps/unix/sysv/linux/syscall-names.list:60:cacheflush
> glibc/benchtests/strcoll-inputs/filelist#en_US.UTF-8:1417:cacheflush.c
> glibc/benchtests/strcoll-inputs/filelist#en_US.UTF-8:1744:cacheflush.c
> glibc/ChangeLog.old/ChangeLog.7:7489:	* sysdeps/mach/mips/cacheflush.c:
> Likewise.
> glibc/ChangeLog.old/ChangeLog.7:9422:	*
> sysdeps/unix/sysv/linux/m68k/syscalls.list: Add cacheflush.
> glibc/ChangeLog.old/ChangeLog.4:205:	* sysdeps/mach/mips/cacheflush.c:
> New file.
> glibc/ChangeLog.old/ChangeLog.18:40858:	*
> sysdeps/unix/sysv/linux/nios2/cacheflush.c: New file.
> glibc/ChangeLog.old/ChangeLog.ports-tile:700:	*
> sysdeps/unix/sysv/linux/tile/cacheflush.c: New file.
> grep: glibc/.git/index: binary file matches
>
> $ grep -rn -e 'sys_cacheflush' -e 'SYSCALL_DEFINE.(cacheflush,' linux/ |
> grep -v -e '/arc/' -e '/csky/' -e '/mips/' -e '/nios2/'
> tools/testing/selftests/futex/functional/usr/include/linux/capability.h:251:/*
> Allow flushing all cache on m68k (sys_cacheflush) */
> include/uapi/linux/capability.h:253:/* Allow flushing all cache on m68k
> (sys_cacheflush) */
> arch/m68k/kernel/sys_m68k.c:376:/* sys_cacheflush -- flush (part of) the
> processor cache.  */
> arch/m68k/kernel/sys_m68k.c:378:sys_cacheflush (unsigned long addr, int
> scope, int cache, unsigned long len)
> arch/m68k/kernel/sys_m68k.c:531:/* sys_cacheflush -- flush (part of) the
> processor cache.  */
> arch/m68k/kernel/sys_m68k.c:533:sys_cacheflush (unsigned long addr, int
> scope, int cache, unsigned long len)
> arch/m68k/kernel/syscalls/syscall.tbl:133:123	common	cacheflush
> sys_cacheflush
> arch/sh/kernel/sys_sh.c:57:/* sys_cacheflush -- flush (part of) the
> processor cache.  */
> arch/sh/kernel/sys_sh.c:58:asmlinkage int sys_cacheflush(unsigned long
> addr, unsigned long len, int op)
> arch/sh/kernel/syscalls/syscall.tbl:133:123	common	cacheflush
> sys_cacheflush
> arch/arm/include/asm/cacheflush.h:263: * This is used for the ARM
> private sys_cacheflush system call.
> arch/nds32/include/uapi/asm/unistd.h:15:__SYSCALL(__NR_cacheflush,
> sys_cacheflush)
> arch/nds32/include/asm/syscalls.h:7:asmlinkage long
> sys_cacheflush(unsigned long addr, unsigned long len, unsigned int op);
> arch/nds32/kernel/sys_nds32.c:29:SYSCALL_DEFINE3(cacheflush, unsigned
> int, start, unsigned int, end, int, cache)
>
> Rendered page (NOTES only):
>
> [
> NOTES
>     Architecture-specific variants
>         Glibc  provides a wrapper for this system call, with the pro‐
>         totype shown in SYNOPSIS, for  the  following  architectures:
>         ARC, CSKY, MIPS, and NIOS2. // lowercase?
>
>         On  some other architectures, Linux provides this system call
>         with different arguments:
>
>         M68K:
>
>             int cacheflush(unsigned long addr, int scope, int cache,
>                            unsigned long len);
>
>         SH:
>
>             int cacheflush(unsigned long addr, unsigned long len, int op);
>
>         NDS32:
>
>             int cacheflush(unsigned int start, unsigned int end, int cache);
>
>         // ARM??
>
>     GCC alternative
>         Unless you need the finer grained control  that  this  system
>         call  provides,  you  probably  want  to use the GCC built-in
>         function __builtin___clear_cache(), which provides a portable
>         interface  across  platforms  supported by GCC and compatible
>         compilers:
>
>             void __builtin___clear_cache(void *begin, void *end);
>
>         On platforms that don't require  instruction  cache  flushes,
>         __builtin___clear_cache() has no effect.
>
>         Note:  On  some  GCC-compatible compilers, such as clang, the
>         prototype for this function uses char * instead of void * for
>         the parameters.
>
> ]
>
> 'GCC alternative' is the name I gave to the NOTES from the other thread,
> which aren't yet merged (I'll send the patches after the weekend, probably).
>
> Subsections based on:
> fadvise64(2)
>
> Can you review this?
>
> Thanks,
>
> Alex
>