Messages in this thread | | | Date | Tue, 25 Aug 2015 03:22:46 -0400 | From | Rich Felker <> | Subject | Re: [PATCH] arch/sh: provide unified syscall trap compatible with all SH models |
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On Tue, Aug 25, 2015 at 09:18:44AM +0200, Geert Uytterhoeven wrote: > 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?
It was an unintended side-effect of restructuring the table to be a list of legacy values. While the actual functional work of this patch was done months ago, I just noticed that the comments should be changed yesterday while preparing the patch for submission. I can rework them to avoid dropping the useful information.
Thanks for the quick initial review!
Rich
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