From mboxrd@z Thu Jan 1 00:00:00 1970 From: Karl Nasrallah Date: Tue, 17 Dec 2019 22:16:28 +0000 Subject: Re: can someone solve string_32.h issue for SH ? Message-Id: <1933127148.546436.1576620988364@mail.yahoo.com> List-Id: References: <87h81zh4ap.wl-kuninori.morimoto.gx@renesas.com> <871rt3gwri.wl-kuninori.morimoto.gx@renesas.com> <1850003495.209647.1576573784839@mail.yahoo.com> In-Reply-To: <1850003495.209647.1576573784839@mail.yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: kuninori.morimoto.gx@renesas.com, geert@linux-m68k.org Cc: ysato@users.sourceforge.jp, dalias@libc.org, linux-sh@vger.kernel.org, linux-renesas-soc@vger.kernel.org Hello! I have a strncpy for you. static inline char *strncpy(char *__dest, const char *__src, size_t __n) { char * retval = __dest; const char * __dest_end = __dest + __n - 1; // size_t is always unsigned if(__n == 0) { return retval; } __asm__ __volatile__ ( "strncpy_start:\n\t" "mov.b @%[src]+,r0\n\t" "cmp/eq #0,r0\n\t" // cmp/eq #imm8,r0 is its own instruction "bt.s strncpy_pad\n\t" // Done with the string "cmp/eq %[dest],%[dest_end]\n\t" // This takes care of the size parameter in only one instruction ;) "bt.s strncpy_end\n\t" "mov.b r0,@%[dest]\n\t" "bra strncpy_start\n\t" "add #1,%[dest]\n\t" // mov.b R0,@Rn+ is SH2A only, but we can fill the delay slot with the offset "strncpy_pad:\n\t" "bt.s strncpy_end\n\t" "mov.b r0,@%[dest]\n\t" "add #1,%[dest]\n\t" "bra strncpy_pad\n\t" "cmp/eq %[dest],%[dest_end]\n\t" "strncpy_end:\n\t" // All done : [src] "+r" (__src), [dest] "+r" (__dest) : [dest_end] "r" (__dest_end) : "t" ); return retval; } Tested with sh4-elf-gcc 9.2.0 on a real SH7750/SH7750R-compatible system. No warnings, behaves exactly as per linux (dot) die (dot) net/man/3/strncpy and I optimized it with some tricks I devised from writing extremely optimized x86. If there are any doubts as to the authenticity, note that I am the sole author of this project: github (dot) com/KNNSpeed/AVX-Memmove Hope this helps! -Karl (P.S. Consider this code public domain. If for whatever reason that doesn't fly, then I give the Linux kernel community explicit permission to use it as they see fit.) -----Original Message----- From: Karl Nasrallah To: kuninori.morimoto.gx ; geert Cc: ysato ; dalias ; linux-sh ; linux-renesas-soc Sent: Tue, Dec 17, 2019 4:09 am Subject: Re: can someone solve string_32.h issue for SH ? Hello, Give me a day or so and I can do the following things: 1) Write you all a brand new standards-conforming strncpy in SH4 asm like this that is easier to read 2) Compile it with sh4-elf-GCC 9.2 3) Test it on a real SH4 (SH7750/SH7750R-like) The warning, if it shows up in my test, would likely then be a GCC thing--I have an idea of what it's doing, but I'll be sure after that. Unfortunately it's 4AM here on the other side of the world right now... -Karl -----Original Message----- From: Kuninori Morimoto To: Geert Uytterhoeven Cc: Yoshinori Sato ; Rich Felker ; Linux-SH ; Linux-Renesas Sent: Tue, Dec 17, 2019 3:51 am Subject: Re: can someone solve string_32.h issue for SH ? Hi Geert Cc Yoshinori-san > > --- a/arch/sh/include/asm/string_32.h > > +++ b/arch/sh/include/asm/string_32.h > > @@ -40,15 +40,15 @@ static inline char *strncpy(char *__dest, const > > char *__src, size_t __n) > >         __asm__ __volatile__( > >                 "1:\n" > >                 "mov.b  @%1+, %2\n\t" > > -               "mov.b  %2, @%0\n\t" > > +               "mov.b  %2, @%0+\n\t" > >                 "cmp/eq #0, %2\n\t" > >                 "bt/s   2f\n\t" > > -               " cmp/eq        %5,%1\n\t" > > +               " cmp/eq        %5,%0\n\t" > >                 "bf/s   1b\n\t" > > -               " add   #1, %0\n" > > +               " nop\n" > >                 "2:" > >                 : "=r" (__dest), "=r" (__src), "=&z" (__dummy) > > -               : "0" (__dest), "1" (__src), "r" (__src+__n) > > +               : "0" (__dest), "1" (__src), "r" (__dest+__n) > >                 : "memory", "t"); > > > >         return __xdest; > > > > Does this make sense? > > Can it be improved, by putting something useful in the delay slot? > > BTW, there seems to be a serious security issue with this strncpy() > implementation: while it never writes more than n bytes in the > destination buffer, it doesn't pad the destination buffer with zeroes if > the source string is shorter than the buffer size.  This will leak > data. Yeah... I can only do is "Reporting issue" to SH ML, unfortunately... Thank you for your help !! Best regards --- Kuninori Morimoto