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 <knnspeed@xxxxxxx>
To: kuninori.morimoto.gx <kuninori.morimoto.gx@xxxxxxxxxxx>; geert <geert@xxxxxxxxxxxxxx>
Cc: ysato <ysato@xxxxxxxxxxxxxxxxxxxx>; dalias <dalias@xxxxxxxx>; linux-sh <linux-sh@xxxxxxxxxxxxxxx>; linux-renesas-soc <linux-renesas-soc@xxxxxxxxxxxxxxx>
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 <kuninori.morimoto.gx@xxxxxxxxxxx>
To: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>; Rich Felker <dalias@xxxxxxxx>; Linux-SH <linux-sh@xxxxxxxxxxxxxxx>; Linux-Renesas <linux-renesas-soc@xxxxxxxxxxxxxxx>
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
