diff options
| author | Helge Deller <deller@gmx.de> | 2008-12-30 02:47:38 +0000 |
|---|---|---|
| committer | Kyle McMartin <kyle@mcmartin.ca> | 2009-03-31 02:51:35 +0000 |
| commit | c84c3a698f17ae5d55a6ecc76298fb894e106336 (patch) | |
| tree | 6b6d1de960a9f189f86bf1d28ec31be110a8b35e /arch/parisc/kernel/syscall.S | |
| parent | 8a1def457bab9f9654bd4dbb1e3eea6fedd26afa (diff) | |
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: Carlos O'Donell <carlos@systemhalted.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
Diffstat (limited to 'arch/parisc/kernel/syscall.S')
| -rw-r--r-- | arch/parisc/kernel/syscall.S | 58 |
1 files changed, 48 insertions, 10 deletions
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S index 69b6eebc466e..59fc1a43ec3e 100644 --- a/arch/parisc/kernel/syscall.S +++ b/arch/parisc/kernel/syscall.S @@ -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 |