Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit c84c3a69 authored by Helge Deller's avatar Helge Deller Committed by Kyle McMartin
Browse files

parisc: document light weight syscall ABI 



Document the LWS ABI including implementation notes for
userspace, and comment cleanup.

Remove extraneous .align 16 after lws_lock_start.

Signed-off-by: default avatarCarlos O'Donell <carlos@systemhalted.org>
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
Signed-off-by: default avatarKyle McMartin <kyle@mcmartin.ca>
parent 8a1def45

arch/parisc/kernel/syscall.S

+48 −10
Original line number Diff line number Diff line
@@ -365,17 +365,51 @@ tracesys_sigexit: 




	/*********************************************************

		Light-weight-syscall code

		32/64-bit Light-Weight-Syscall ABI



		r20 - lws number

		r26,r25,r24,r23,r22 - Input registers

		r28 - Function return register

		r21 - Error code.

		* - Indicates a hint for userspace inline asm

		implementations.



		Scracth: Any of the above that aren't being

		currently used, including r1. 

		Syscall number (caller-saves)

	        - %r20

	        * In asm clobber.



		Return pointer: r31 (Not usable)

		Argument registers (caller-saves)

	        - %r26, %r25, %r24, %r23, %r22

	        * In asm input.



		Return registers (caller-saves)

	        - %r28 (return), %r21 (errno)

	        * In asm output.



		Caller-saves registers

	        - %r1, %r27, %r29

	        - %r2 (return pointer)

	        - %r31 (ble link register)

	        * In asm clobber.



		Callee-saves registers

	        - %r3-%r18

	        - %r30 (stack pointer)

	        * Not in asm clobber.



		If userspace is 32-bit:

		Callee-saves registers

	        - %r19 (32-bit PIC register)



		Differences from 32-bit calling convention:

		- Syscall number in %r20

		- Additional argument register %r22 (arg4)

		- Callee-saves %r19.



		If userspace is 64-bit:

		Callee-saves registers

		- %r27 (64-bit PIC register)



		Differences from 64-bit calling convention:

		- Syscall number in %r20

		- Additional argument register %r22 (arg4)

		- Callee-saves %r27.



		Error codes returned by entry path:
@@ -473,7 +507,8 @@ lws_compare_and_swap64: 
	b,n	lws_compare_and_swap

#else

	/* If we are not a 64-bit kernel, then we don't

	 * implement having 64-bit input registers

	 * have 64-bit input registers, and calling

	 * the 64-bit LWS CAS returns ENOSYS.

	 */

	b,n	lws_exit_nosys

#endif
@@ -635,12 +670,15 @@ END(sys_call_table64) 
	/*

		All light-weight-syscall atomic operations 

		will use this set of locks 



		NOTE: The lws_lock_start symbol must be

		at least 16-byte aligned for safe use

		with ldcw.

	*/

	.section .data

	.align	PAGE_SIZE

ENTRY(lws_lock_start)

	/* lws locks */

	.align 16

	.rept 16

	/* Keep locks aligned at 16-bytes */

	.word 1