Ping?
On Tue, Aug 25, 2015 at 05:23:11PM -0400, Rich Felker wrote: > From: Rich Felker <[email protected]> > > 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 <[email protected]> > > --- > > The original proposal for using 0x1f as a unified syscall trap was > reviewed by Jeff Dionne, Yoshinori Sato, and Shumpei Kawasaki for > conflicts with existing trap number assignments, and none were found. > I introduced this proposal as a way to add SH-2 support to musl libc > in a forwards-compatible way, treating SH as a unified architecture, > with the particular intent of supporting the Open Processor > Foundation's J2 Core (SH-2 ISA plus some extensions) and providing a > smooth upgrade path to the future J4 Core (SH-4 equivalent) and other > full-fledged SH platforms with MMU. > > There is also some interest in having glibc's SH port support SH-2/J2, > which is more practical with a common syscall ABI; whether this will > actually happen remains uncertain. > > Version 2 of the patch addresses issues raised by Geert Uytterhoeven > with the changes to comments in entry-common.S. > > Rich > > > > diff -urp ../linux-4.2-rc6.orig/arch/sh/kernel/cpu/sh2/entry.S > ./arch/sh/kernel/cpu/sh2/entry.S > --- ../linux-4.2-rc6.orig/arch/sh/kernel/cpu/sh2/entry.S 2015-08-09 > 19:54:30.000000000 +0000 > +++ ./arch/sh/kernel/cpu/sh2/entry.S 2015-08-24 03:23:34.159387924 +0000 > @@ -144,9 +144,9 @@ ENTRY(exception_handler) > mov #64,r8 > cmp/hs r8,r9 > bt interrupt_entry ! vec >= 64 is interrupt > - mov #32,r8 > + mov #31,r8 > cmp/hs r8,r9 > - bt trap_entry ! 64 > vec >= 32 is trap > + bt trap_entry ! 64 > vec >= 31 is trap > > mov.l 4f,r8 > mov r9,r4 > @@ -178,9 +178,9 @@ interrupt_entry: > > trap_entry: > mov #0x30,r8 > - cmp/ge r8,r9 ! vector 0x20-0x2f is systemcall > + cmp/ge r8,r9 ! vector 0x1f-0x2f is systemcall > bt 1f > - add #-0x10,r9 ! convert SH2 to SH3/4 ABI > + mov #0x1f,r9 ! convert to unified SH2/3/4 trap number > 1: > shll2 r9 ! TRA > bra system_call ! jump common systemcall entry > diff -urp ../linux-4.2-rc6.orig/arch/sh/kernel/cpu/sh2a/entry.S > ./arch/sh/kernel/cpu/sh2a/entry.S > --- ../linux-4.2-rc6.orig/arch/sh/kernel/cpu/sh2a/entry.S 2015-08-09 > 19:54:30.000000000 +0000 > +++ ./arch/sh/kernel/cpu/sh2a/entry.S 2015-08-24 03:23:58.849386418 +0000 > @@ -109,9 +109,9 @@ ENTRY(exception_handler) > mov #64,r8 > cmp/hs r8,r9 > bt interrupt_entry ! vec >= 64 is interrupt > - mov #32,r8 > + mov #31,r8 > cmp/hs r8,r9 > - bt trap_entry ! 64 > vec >= 32 is trap > + bt trap_entry ! 64 > vec >= 31 is trap > > mov.l 4f,r8 > mov r9,r4 > @@ -143,9 +143,9 @@ interrupt_entry: > > trap_entry: > mov #0x30,r8 > - cmp/ge r8,r9 ! vector 0x20-0x2f is systemcall > + cmp/ge r8,r9 ! vector 0x1f-0x2f is systemcall > bt 1f > - add #-0x10,r9 ! convert SH2 to SH3/4 ABI > + mov #0x1f,r9 ! convert to unified SH2/3/4 trap number > 1: > shll2 r9 ! TRA > bra system_call ! jump common systemcall entry > diff -urp ../linux-4.2-rc6.orig/arch/sh/kernel/entry-common.S > ./arch/sh/kernel/entry-common.S > --- ../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 2015-08-25 21:08:15.835463227 +0000 > @@ -268,20 +268,29 @@ 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: See following table. > * > - * 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. > + * 0x1f unified SH-2/3/4 syscall ABI (preferred). > + * 0x20-0x2f original SH-2 syscall ABI. > * 0x30-0x3f debug traps used by the kernel. > * 0x40-0xff Not supported by all parts, so left unhandled. > * > + * For making system calls, any trap number in the range for the > + * given cpu model may be used, but the unified trap number 0x1f is > + * preferred for compatibility with all models. > + * > + * The low bits of the trap number were once documented as matching > + * the number of arguments, but they were never actually used as such > + * by the kernel. SH-2 originally used its own separate trap range > + * because several hardware exceptions fell in the range used for the > + * SH-3/4 syscall ABI. > + * > + * 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" > * argument. > -- > To unsubscribe from this list: send the line "unsubscribe linux-sh" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
