From: "Zhangjian (Bamvor)" Subject: Re: [RFC PATCH] sys_read: add a compat_sys_read for 64bit system Date: Wed, 8 Jun 2016 10:14:41 +0800 Message-ID: <57577F91.5080308@huawei.com> References: <575775FA.1080009@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <575775FA.1080009@huawei.com> Sender: linux-kernel-owner@vger.kernel.org To: Weidong Wang , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, viro@zeniv.linux.org.uk, arnd@arndb.de Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Hanjun Guo , "Zhangjian (Bamvor)" , Linux-Api List-Id: linux-api@vger.kernel.org Hi, On 2016/6/8 9:33, Weidong Wang wrote: > Test 32 progress and 64 progress on the 64bit system with > this progress: > > int main(int argc, char **argv) > { > int fd = 0; > int i, ret = 0; > char buf[512]; > unsigned long count = -1; > > fd = open("/tmp", O_RDONLY); > if (fd < -1) { > printf("Pls check the directory is exist?\n"); > return -1; > } > errno = 0; > ret = read(fd, NULL, count); > printf("Ret is %d errno %d\n", ret, errno); > close(fd); > > return 0; > } > > we get the different errno. The 64 progress we get errno is -14 while > the 32 progress is -21. > > The reason is that, the user progress would use a 32bit count, while > the sys_read size_t in kernel is 64bit. When the uesrspace count is > -1(0xffffffff), it goes to the sys_read, it would be change to a positive > number. > > So I think we should add a compat_sys_read for the read syscall. I test it > on x86 or arm64 platform. The patch works well. As weidong said, we tested on x86, x86_64, aarch64 ilp32, aarch64 lp64. We do not familiar with other architecture, cc linux-api, hope could get more input. Regards Bamvor > > As well this patch may do work for the 'tile' 64 system. > I think it may enter the same result on mips/parisc/powerpc/sparc. > The s390 do the compat_sys_s390_read for the compat sys_read. > > Signed-off-by: Weidong Wang > --- > arch/x86/entry/syscalls/syscall_32.tbl | 2 +- > fs/read_write.c | 8 ++++++++ > include/linux/compat.h | 2 ++ > include/uapi/asm-generic/unistd.h | 2 +- > 4 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl > index 4cddd17..ebc24e3 100644 > --- a/arch/x86/entry/syscalls/syscall_32.tbl > +++ b/arch/x86/entry/syscalls/syscall_32.tbl > @@ -9,7 +9,7 @@ > 0 i386 restart_syscall sys_restart_syscall > 1 i386 exit sys_exit > 2 i386 fork sys_fork sys_fork > -3 i386 read sys_read > +3 i386 read sys_read compat_sys_read > 4 i386 write sys_write > 5 i386 open sys_open compat_sys_open > 6 i386 close sys_close > diff --git a/fs/read_write.c b/fs/read_write.c > index 933b53a..d244848 100644 > --- a/fs/read_write.c > +++ b/fs/read_write.c > @@ -613,6 +613,14 @@ SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf, > return ret; > } > > +#ifdef CONFIG_COMPAT > +COMPAT_SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, > + compat_size_t, count) > +{ > + return sys_read(fd, buf, (compat_ssize_t)count); > +} > +#endif > + > SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf, > size_t, count, loff_t, pos) > { > diff --git a/include/linux/compat.h b/include/linux/compat.h > index f964ef7..d88ccad 100644 > --- a/include/linux/compat.h > +++ b/include/linux/compat.h > @@ -332,6 +332,8 @@ asmlinkage long compat_sys_keyctl(u32 option, > u32 arg2, u32 arg3, u32 arg4, u32 arg5); > asmlinkage long compat_sys_ustat(unsigned dev, struct compat_ustat __user *u32); > > +asmlinkage ssize_t compat_sys_read(unsigned int fd, > + char __user * buf, compat_size_t count); > asmlinkage ssize_t compat_sys_readv(compat_ulong_t fd, > const struct compat_iovec __user *vec, compat_ulong_t vlen); > asmlinkage ssize_t compat_sys_writev(compat_ulong_t fd, > diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h > index a26415b..745818a 100644 > --- a/include/uapi/asm-generic/unistd.h > +++ b/include/uapi/asm-generic/unistd.h > @@ -201,7 +201,7 @@ __SC_COMP(__NR_getdents64, sys_getdents64, compat_sys_getdents64) > #define __NR3264_lseek 62 > __SC_3264(__NR3264_lseek, sys_llseek, sys_lseek) > #define __NR_read 63 > -__SYSCALL(__NR_read, sys_read) > +__SC_COMP(__NR_read, sys_read, compat_sys_read) > #define __NR_write 64 > __SYSCALL(__NR_write, sys_write) > #define __NR_readv 65 >