From 28ea4b3f4c16e880ee2f9246d915508398056f09 Mon Sep 17 00:00:00 2001
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Sun, 21 Jun 2020 19:35:04 +1000
Subject: [PATCH] software/microwatt: Fix copying data to RAM and clearing BSS

This also makes us use the "small" memory model to avoid having to
use more complex constructs and adds the TOC to the linker script

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 litex/soc/cores/cpu/microwatt/core.py |  1 +
 litex/soc/cores/cpu/microwatt/crt0.S  | 42 +++++++++++++++++++++++----
 litex/soc/software/bios/linker.ld     |  1 +
 3 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/litex/soc/cores/cpu/microwatt/core.py b/litex/soc/cores/cpu/microwatt/core.py
index 45da6e69d..ee6f8a66e 100644
--- a/litex/soc/cores/cpu/microwatt/core.py
+++ b/litex/soc/cores/cpu/microwatt/core.py
@@ -41,6 +41,7 @@ class Microwatt(CPU):
         flags += "-mlittle-endian "
         flags += "-mstrict-align "
         flags += "-fno-stack-protector "
+        flags += "-mcmodel=small "
         flags += "-D__microwatt__ "
         return flags
 
diff --git a/litex/soc/cores/cpu/microwatt/crt0.S b/litex/soc/cores/cpu/microwatt/crt0.S
index e03ac0bb4..0fc8868ef 100644
--- a/litex/soc/cores/cpu/microwatt/crt0.S
+++ b/litex/soc/cores/cpu/microwatt/crt0.S
@@ -41,12 +41,44 @@
 _start:
 	FIXUP_ENDIAN
 
+	/* Grab our own address */
+	bcl	20,31,$+4
+0:	mflr	%r12
+
+	/* Get our TOC */
+	addis	%r2,%r12,(.TOC.-0b)@h
+	addi	%r2,%r2,(.TOC.-0b)@l
+
+	/* Copy data from ROM to SRAM */
+	ld	%r3,_fdata@got(%r2)
+	ld	%r4,_edata@got(%r2)
+	ld	%r5,_fdata_rom@got(%r2)
+	subf	%r6,%r3,%r4
+	srdi.	%r6,%r6,3
+	beq	1f
+	li	%r10,0
+	mtctr	%r6
+0:	ldx	%r0,%r10,%r5
+	stdx	%r0,%r10,%r3
+	addi	%r10,%r10,8
+	bdnz	0b
+1:
+	/* Clear BSS */
+	ld	%r3,_fbss@got(%r2)
+	ld	%r4,_ebss@got(%r2)
+	subf	%r6,%r3,%r4
+	srdi.	%r6,%r6,3
+	beq	1f
+	li	%r0,0
+	subi	%r3,%r3,8
+	mtctr	%r6
+0:	stdu	%r0,8(%r3)
+	bdnz	0b
+1:
 	/* setup stack */
-	LOAD_IMM64(%r1, _fstack - 0x100)
-	LOAD_IMM64(%r12, main)
-	mtctr	%r12,
-	bctrl
-	b .
+	ld	%r1,_fstack@got(%r2)
+	bl	main
+	b	.
 
 #define EXCEPTION(nr)		\
 	.=  nr;      \
diff --git a/litex/soc/software/bios/linker.ld b/litex/soc/software/bios/linker.ld
index 070212538..6ebd50cdd 100644
--- a/litex/soc/software/bios/linker.ld
+++ b/litex/soc/software/bios/linker.ld
@@ -25,6 +25,7 @@ SECTIONS
 		*(.rodata .rodata.* .gnu.linkonce.r.*)
 		*(.rodata1)
 		*(.got .got.*)
+		*(.toc .toc.*)
 
 		/* Make sure the file is aligned on disk as well
 		   as in memory; CRC calculation requires that. */