From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Sun, 21 Jun 2020 09:35:04 +0000 (+1000)
Subject: software/microwatt: Fix copying data to RAM and clearing BSS
X-Git-Tag: 24jan2021_ls180~169^2
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=28ea4b3f4c16e880ee2f9246d915508398056f09;p=litex.git

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>
---

diff --git a/litex/soc/cores/cpu/microwatt/core.py b/litex/soc/cores/cpu/microwatt/core.py
index 45da6e69..ee6f8a66 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 e03ac0bb..0fc8868e 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 07021253..6ebd50cd 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. */