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 45da6e69d635c75ac8d6fed003a998d50534b539..ee6f8a66e73845370fa4fb53e8dd6b68d6cff79f 100644 (file)
--- 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 e03ac0bb4be6e07239efb0cbb9c7724c3badf3c2..0fc8868ef0c2269e4f4bcd978a61243c7b521d62 100644 (file)
--- 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 070212538958d9ace8e8ff0c9c6738ebd8ac8491..6ebd50cdd709fc0fd6b529cdc384dc10811ec56a 100644 (file)
--- 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. */