[OpenBIOS] [PATCH 2/4] SPARC64: reduce client interface stack usage

[Mark Cave-Ayland]

Currently the client interface entrypoint uses the existing client stack to
save state before invoking the main C implementation function. Unfortunately
some clients such as OpenBSD have a very small stack available which can be
exhausted by internal OpenBIOS calls.

Reduce the stack space required by just saving the globals onto the existing
stack and instead switching to a separate stack when invoking the OpenBIOS
client interface.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland at ilande.co.uk>
---
 openbios-devel/arch/sparc64/call-client.S |   67 ++++++++++++++++++++---------
 1 file changed, 46 insertions(+), 21 deletions(-)

diff --git a/openbios-devel/arch/sparc64/call-client.S b/openbios-devel/arch/sparc64/call-client.S
index d15f177..18de704 100644
--- a/openbios-devel/arch/sparc64/call-client.S
+++ b/openbios-devel/arch/sparc64/call-client.S
@@ -2,8 +2,12 @@
 
 	.data
 	.align	8
-client_globals:
-	.skip 64
+
+	.skip	16384
+openbios_stack:
+
+client_stack:
+	.xword	0
 
 	.text
 	.align	4
@@ -19,26 +23,47 @@ client_globals:
 sparc64_of_client_interface:
 	/* make sure caller's windows are on caller's stack */
 	flushw
-	save %sp, -248, %sp
-	stx	    %g1, [%sp + 2047 + 192 +  0]
-	stx	    %g2, [%sp + 2047 + 192 +  8]
-	stx	    %g3, [%sp + 2047 + 192 + 16]
-	stx	    %g4, [%sp + 2047 + 192 + 24]
-	stx	    %g5, [%sp + 2047 + 192 + 32]
-	stx	    %g6, [%sp + 2047 + 192 + 40]
-	stx	    %g7, [%sp + 2047 + 192 + 48]
+
+	/* Save globals on callers stack */
+	add	%sp, -56, %sp
+
+	stx	%g1, [%sp + 2047 + 0]
+	stx	%g2, [%sp + 2047 + 8]
+	stx	%g3, [%sp + 2047 + 16]
+	stx	%g4, [%sp + 2047 + 24]
+	stx	%g5, [%sp + 2047 + 32]
+	stx	%g6, [%sp + 2047 + 40]
+	stx	%g7, [%sp + 2047 + 48]
+
+	/* Save existing stack and move to openbios stack */
+	setx	client_stack, %g6, %g7
+	stx	%sp, [%g7]
+	setx	openbios_stack - 2047 - 192, %g6, %g7
+	mov	%g7, %sp
+
+	/* Call client inteface */
+	save	%sp, -192, %sp
 
 	call of_client_interface
 	 mov %i0, %o0
-	mov %o0, %i0
-
-	ldx	    [%sp + 2047 + 192 +  0], %g1
-	ldx	    [%sp + 2047 + 192 +  8], %g2
-	ldx	    [%sp + 2047 + 192 + 16], %g3
-	ldx	    [%sp + 2047 + 192 + 24], %g4
-	ldx	    [%sp + 2047 + 192 + 32], %g5
-	ldx	    [%sp + 2047 + 192 + 40], %g6
-	ldx	    [%sp + 2047 + 192 + 48], %g7
-	return  %i7+8
-	 nop
 
+	mov	%o0, %i0
+	restore	%sp, 192, %sp
+
+	/* Restore stack */
+	setx	client_stack, %g6, %g7
+	ldx	[%g7], %sp
+
+	/* Restore globals */
+	ldx	[%sp + 2047 + 0], %g1
+	ldx	[%sp + 2047 + 8], %g2
+	ldx	[%sp + 2047 + 16], %g3
+	ldx	[%sp + 2047 + 24], %g4
+	ldx	[%sp + 2047 + 32], %g5
+	ldx	[%sp + 2047 + 40], %g6
+	ldx	[%sp + 2047 + 48], %g7
+
+	add	%sp, 56, %sp
+
+	jmp	%o7+8
+	 nop
-- 
1.7.10.4