s390/boot: workaround llvm IAS bug

For at least the mvc and clc instructions llvm's integrated assembler can
generate incorrect code. In particular this happens with decompressor boot
code. The reason seems to be that relocations for the second displacement
of each instruction are at incorrect locations (-/+: gas vs llvm IAS):

mvc     __LC_IO_NEW_PSW(16),.Lnewpsw

results in

        4:      d2 0f 01 f0 00 00       mvc     496(16,%r0),0
-                       8: R_390_12     .head.text+0x10
+		       6: R_390_12     .head.text+0x10

and
clc     0(3,%r4),.L_hdr
results in

      258:      d5 02 40 00 00 00       clc     0(3,%r4),0
-                       25c: R_390_12   .head.text+0x324
+		       25a: R_390_12   .head.text+0x324

Workaround this by writing the code in a different way.

Tested-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://github.com/llvm/llvm-project/issues/55411
Link: https://lore.kernel.org/r/20220511120532.2228616-7-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/boot/head.S

@@ -42,7 +42,8 @@ ipl_start:
 # subroutine to wait for end I/O
 #
 .Lirqwait:
-	mvc	__LC_IO_NEW_PSW(16),.Lnewpsw	# set up IO interrupt psw
+	larl	%r13,.Lnewpsw		# set up IO interrupt psw
+	mvc	__LC_IO_NEW_PSW(16),0(%r13)
 	lpsw	.Lwaitpsw
 .Lioint:
 	br	%r14
@@ -155,9 +156,11 @@ ipl_start:
 	lr	%r2,%r3
 .Lnotrunc:
 	l	%r4,.Linitrd
-	clc	0(3,%r4),.L_hdr		# if it is HDRx
+	larl	%r13,.L_hdr
+	clc	0(3,%r4),0(%r13)	# if it is HDRx
 	bz	.Lagain1		# skip dataset header
-	clc	0(3,%r4),.L_eof		# if it is EOFx
+	larl	%r13,.L_eof
+	clc	0(3,%r4),0(%r13)	# if it is EOFx
 	bz	.Lagain1		# skip dateset trailer
 
 	lr	%r5,%r2
@@ -181,9 +184,11 @@ ipl_start:
 .Lrdcont:
 	l	%r2,.Linitrd
 
-	clc	0(3,%r2),.L_hdr		# skip HDRx and EOFx
+	larl	%r13,.L_hdr		# skip HDRx and EOFx
+	clc	0(3,%r2),0(%r13)
 	bz	.Lagain2
-	clc	0(3,%r2),.L_eof
+	larl	%r13,.L_eof
+	clc	0(3,%r2),0(%r13)
 	bz	.Lagain2
 
 #
@@ -260,20 +265,23 @@ SYM_CODE_START_LOCAL(startup_normal)
 	.fill	16,4,0x0
 0:	lmh	%r0,%r15,0(%r13)	# clear high-order half of gprs
 	sam64				# switch to 64 bit addressing mode
-	basr	%r13,0			# get base
+	larl	%r13,.Lext_new_psw
-.LPG0:
+	mvc	__LC_EXT_NEW_PSW(16),0(%r13)
-	mvc	__LC_EXT_NEW_PSW(16),.Lext_new_psw-.LPG0(%r13)
+	larl	%r13,.Lpgm_new_psw
-	mvc	__LC_PGM_NEW_PSW(16),.Lpgm_new_psw-.LPG0(%r13)
+	mvc	__LC_PGM_NEW_PSW(16),0(%r13)
-	mvc	__LC_IO_NEW_PSW(16),.Lio_new_psw-.LPG0(%r13)
+	larl	%r13,.Lio_new_psw
+	mvc	__LC_IO_NEW_PSW(16),0(%r13)
 	xc	0x200(256),0x200	# partially clear lowcore
 	xc	0x300(256),0x300
 	xc	0xe00(256),0xe00
 	xc	0xf00(256),0xf00
-	lctlg	%c0,%c15,.Lctl-.LPG0(%r13)	# load control registers
+	larl	%r13,.Lctl
+	lctlg	%c0,%c15,0(%r13)	# load control registers
 	stcke	__LC_BOOT_CLOCK
 	mvc	__LC_LAST_UPDATE_CLOCK(8),__LC_BOOT_CLOCK+1
-	spt	6f-.LPG0(%r13)
+	larl	%r13,6f
-	mvc	__LC_LAST_UPDATE_TIMER(8),6f-.LPG0(%r13)
+	spt	0(%r13)
+	mvc	__LC_LAST_UPDATE_TIMER(8),0(%r13)
 	larl	%r15,_stack_end-STACK_FRAME_OVERHEAD
 	brasl	%r14,sclp_early_setup_buffer
 	brasl	%r14,verify_facilities