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Commit 57e26e57 authored by Vineet Gupta's avatar Vineet Gupta
Browse files

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: default avatarNoam Camus <noamc@ezchip.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 3aa4f80e

arch/arc/kernel/ctx_sw.c

+12 −1
Original line number Diff line number Diff line
@@ -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 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task) 
#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 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task) 
		/* 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"

	);

arch/arc/kernel/ctx_sw_asm.S

+9 −2
Original line number Diff line number Diff line
@@ -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 @@ __switch_to: 
	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.