Re: [PATCH] arch/sh: provide unified syscall trap compatible with all SH models
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 wrote: > > From: Rich Felker > > > > 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 > > > --- ../linux-4.2-rc6.orig/arch/sh/kernel/entry-common.S 2015-08-09 > > 19:54:30.0 + > > +++ ./arch/sh/kernel/entry-common.S 2015-08-24 03:33:50.062683702 + > > @@ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] arch/sh: provide unified syscall trap compatible with all SH models
Hi Rich,
On Tue, Aug 25, 2015 at 5:03 AM, Rich Felker wrote:
> From: Rich Felker
>
> 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
> --- ../linux-4.2-rc6.orig/arch/sh/kernel/entry-common.S 2015-08-09
> 19:54:30.0 +
> +++ ./arch/sh/kernel/entry-common.S 2015-08-24 03:33:50.062683702 +
> @@ -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 -- ge...@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
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[PATCH] arch/sh: provide unified syscall trap compatible with all SH models
From: Rich Felker 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 --- 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. 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.S2015-08-09 19:54:30.0 + +++ ./arch/sh/kernel/cpu/sh2/entry.S2015-08-24 03:23:34.159387924 + @@ -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 19:54:30.0 + +++ ./arch/sh/kernel/cpu/sh2a/entry.S 2015-08-24 03:23:58.849386418 + @@ -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 19:54:30.0 + +++ ./arch/sh/kernel/entry-common.S 2015-08-24 03:33:50.062683702 + @@ -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 * --
