sparc64/ofwboot: initialize BSS before entering

tech@,

OpenBIOS's init-program ELF loader claims p_memsz bytes for each
segment, but copies only p_filesz bytes and leaves the remaining memory
untouched. This lets stale firmware memory appear as initialized BSS.

This became visible after shrinking ofwboot by using not -O2 to build it
with LLVM toolchain, tested with -Oz, -Os and -O1.

As result, freelist head moved twelve bytes beyond the file-backed
PT_LOAD range and contained an unaligned garbage pointer, causing
T_ALIGN in alloc().

Ok?

Index: sys/arch/sparc64/stand/ofwboot/srt0.s
===================================================================
RCS file: /home/cvs/src/sys/arch/sparc64/stand/ofwboot/srt0.s,v
diff -u -p -r1.8 srt0.s
--- sys/arch/sparc64/stand/ofwboot/srt0.s	14 Nov 2025 19:17:13 -0000	1.8
+++ sys/arch/sparc64/stand/ofwboot/srt0.s	17 Aug 2026 23:23:37 -0000
@@ -92,6 +92,13 @@ _start:
 	clr	%g4		! Point %g4 to start of data segment
 				! only problem is that apparently the
 				! start of the data segment is 0
+
+	/* OpenBIOS init-program does not clear the ELF BSS. */
+	set	__bss_start, %o0
+	clr	%o1
+	set	_end, %o2
+	call	memset
+	 sub	%o2, %o0, %o2
 	
 	/*
 	 * XXXXXXXX Need to determine what params are passed


-- 
wbr, Kirill