Messages in this thread | | | Date | Tue, 25 Aug 2015 09:18:44 +0200 | Subject | Re: [PATCH] arch/sh: provide unified syscall trap compatible with all SH models | From | Geert Uytterhoeven <> |
| |
Hi Rich,
On Tue, Aug 25, 2015 at 5:03 AM, Rich Felker <dalias@libc.org> wrote: > From: Rich Felker <dalias@libc.org> > > Historically SH-2 Linux (and originally uClinux) used a syscall > calling convention incompatible with the established SH-3/4 Linux ABI. > This choice was made because the trap range used by the existing ABI, > 0x10-0x17, overlaps with the hardware exception/interrupt trap range > reserved by SH-2, and in particular, with the SH-2A divide-by-zero and > division-overflow exceptions. > > Despite the documented syscall convention using the low bits of the > trap number to signal the number of arguments the kernel should > expect, no version of the kernel has ever used this information, nor > is it useful; all of the registers need to be saved anyway. Therefore, > it is possible to pick a new trap number, 0x1f, that is both supported > by all existing SH-3/4 kernels and unassigned as a hardware trap in > the SH-2 range. This makes it possible to produce SH-2 application > binaries that are forwards-compatible with running on SH-3/4 kernels > and to treat SH as a unified platform with varying ISA support levels > rather than multiple gratuitously-incompatible platforms. > > This patch adjusts the range checking SH-2 and SH-2A kernels make for > the syscall trap to accept the range 0x1f-0x2f rather than just > 0x20-0x2f. As a result, trap 0x1f now acts as a syscall for all SH > models. > > Signed-off-by: Rich Felker <dalias@libc.org>
> --- ../linux-4.2-rc6.orig/arch/sh/kernel/entry-common.S 2015-08-09 19:54:30.000000000 +0000 > +++ ./arch/sh/kernel/entry-common.S 2015-08-24 03:33:50.062683702 +0000 > @@ -268,19 +268,20 @@ debug_trap: > * Syscall #: R3 > * Arguments #0 to #3: R4--R7 > * Arguments #4 to #6: R0, R1, R2 > - * TRA: (number of arguments + ABI revision) x 4 > + * TRA>>2: 0x1f, or one of a model-specific set of legacy values: > * > - * This code also handles delegating other traps to the BIOS/gdb stub > - * according to: > - * > - * Trap number > * (TRA>>2) Purpose > * -------- ------- > * 0x00-0x0f original SH-3/4 syscall ABI (not in general use). > * 0x10-0x1f general SH-3/4 syscall ABI. > - * 0x20-0x2f syscall ABI for SH-2 parts. > - * 0x30-0x3f debug traps used by the kernel. > - * 0x40-0xff Not supported by all parts, so left unhandled.
Why did you remoe the two lines of documentation above?
> + * 0x20-0x2f original SH-2 syscall ABI. > + * > + * SH-2 originally used a separate trap range because several hardware > + * exceptions fell in the range used for the SH-3/4 syscall ABI. These > + * are still supported, but trap 0x1f is preferred because it is > + * compatible with all models. > + * > + * This code also handles delegating other traps to the BIOS/gdb stub. > * > * Note: When we're first called, the TRA value must be shifted > * right 2 bits in order to get the value that was used as the "trapa" Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
| |