[PATCH] sh: lib: Restore r4 in shift helpers

[PATCH] sh: lib: Restore r4 in shift helpers

[Florian Fuchs]

Commit 940d4113f330 ("sh: New gcc support") added new shift helpers
that use r4 as a scratch register while dispatching to the selected shift
sequence. But, the helpers return without restoring r4. With GCC 17, the
register allocator can keep a live value in r4 across the helper call.
Clobbering it results in runtime data corruption. Restore r4 before
jumping to the selected shift sequence.

Fixes: 940d4113f330 ("sh: New gcc support")
Signed-off-by: Florian Fuchs <fuchsfl@gmail.com>
---
Without the patch, the early boot on e.g J2 gets a kernel BUG at
mm/percpu.c:2604 / "can't handle more than one group."
        PCPU_SETUP_BUG_ON(pcpu_verify_alloc_info(ai) < 0);
As the static condition in mm/percpu-km.c wasn't true:
        ai->nr_groups != 1
nr_groups contained 60 - the clobbered value from the shift helper.

This change was tested on the J2 core on the Mimas v2 board. It can
theoretically also target other SH2 devices, but I don't have any other
than J2 sadly.

The flow of operations matches now the state in the libgcc, see also
in gcc: libgcc/config/sh/lib1funcs.S
---
 arch/sh/lib/ashlsi3.S | 3 ++-
 arch/sh/lib/ashrsi3.S | 3 ++-
 arch/sh/lib/lshrsi3.S | 3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/sh/lib/ashlsi3.S b/arch/sh/lib/ashlsi3.S
index 4df4401cdf31..73a9d709b169 100644
--- a/arch/sh/lib/ashlsi3.S
+++ b/arch/sh/lib/ashlsi3.S
@@ -63,8 +63,9 @@ __ashlsi3_r0:
 	mova	ashlsi3_table,r0
 	mov.b	@(r0,r4),r4
 	add	r4,r0
+	mov.l	@r15+,r4
 	jmp	@r0
-	mov.l	@r15+,r0
+	mov	r4,r0
 
 	.align	2
 ashlsi3_table:
diff --git a/arch/sh/lib/ashrsi3.S b/arch/sh/lib/ashrsi3.S
index bf3c4e03e6ff..9962d7c587df 100644
--- a/arch/sh/lib/ashrsi3.S
+++ b/arch/sh/lib/ashrsi3.S
@@ -62,8 +62,9 @@ __ashrsi3_r0:
 	mova	ashrsi3_table,r0
 	mov.b	@(r0,r4),r4
 	add	r4,r0
+	mov.l	@r15+,r4
 	jmp	@r0
-	mov.l	@r15+,r0
+	mov	r4,r0
 
 	.align	2
 ashrsi3_table:
diff --git a/arch/sh/lib/lshrsi3.S b/arch/sh/lib/lshrsi3.S
index b79b8170061f..9218f0bad1cc 100644
--- a/arch/sh/lib/lshrsi3.S
+++ b/arch/sh/lib/lshrsi3.S
@@ -62,8 +62,9 @@ __lshrsi3_r0:
 	mova	lshrsi3_table,r0
 	mov.b	@(r0,r4),r4
 	add	r4,r0
+	mov.l	@r15+,r4
 	jmp	@r0
-	mov.l	@r15+,r0
+	mov	r4,r0
 
 	.align	2
 lshrsi3_table:
-- 
2.43.0