ARC: [SMP] Fix build failures for large NR_CPUS
ST.as only takes S9 (255) for offset. This was going out of range when
accessing a task_struct field with 4k NR_CPUS (due to 128b of coumaks
itself in there).
Workaround by using an intermediate register to do the address scaling.
There is some duplication of fix for ctx_sw.c and ctx_sw_asm.S however
given that C version will go away soon I'm not bothering to factor out
the common code.
Reported-by: Noam Camus <noamc@ezchip.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
index 34410eb..c14a5be 100644
--- a/arch/arc/kernel/ctx_sw.c
+++ b/arch/arc/kernel/ctx_sw.c
@@ -17,6 +17,8 @@
#include <asm/asm-offsets.h>
#include <linux/sched.h>
+#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
+
struct task_struct *__sched
__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
{
@@ -45,7 +47,16 @@
#endif
/* set ksp of outgoing task in tsk->thread.ksp */
+#if KSP_WORD_OFF <= 255
"st.as sp, [%3, %1] \n\t"
+#else
+ /*
+ * Workaround for NR_CPUS=4k
+ * %1 is bigger than 255 (S9 offset for st.as)
+ */
+ "add2 r24, %3, %1 \n\t"
+ "st sp, [r24] \n\t"
+#endif
"sync \n\t"
@@ -97,7 +108,7 @@
/* FP/BLINK restore generated by gcc (standard func epilogue */
: "=r"(tmp)
- : "n"((TASK_THREAD + THREAD_KSP) / 4), "r"(next), "r"(prev)
+ : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
: "blink"
);
diff --git a/arch/arc/kernel/ctx_sw_asm.S b/arch/arc/kernel/ctx_sw_asm.S
index d897234..65690e7 100644
--- a/arch/arc/kernel/ctx_sw_asm.S
+++ b/arch/arc/kernel/ctx_sw_asm.S
@@ -14,6 +14,8 @@
#include <asm/asm-offsets.h>
#include <asm/linkage.h>
+#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
+
;################### Low Level Context Switch ##########################
.section .sched.text,"ax",@progbits
@@ -28,8 +30,13 @@
SAVE_CALLEE_SAVED_KERNEL
/* Save the now KSP in task->thread.ksp */
- st.as sp, [r0, (TASK_THREAD + THREAD_KSP)/4]
-
+#if KSP_WORD_OFF <= 255
+ st.as sp, [r0, KSP_WORD_OFF]
+#else
+ /* Workaround for NR_CPUS=4k as ST.as can only take s9 offset */
+ add2 r24, r0, KSP_WORD_OFF
+ st sp, [r24]
+#endif
/*
* Return last task in r0 (return reg)
* On ARC, Return reg = First Arg reg = r0.