MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS

Userland code may be built using an ABI which permits linking to objects
that have more restrictive floating point requirements. For example,
userland code may be built to target the O32 FPXX ABI. Such code may be
linked with other FPXX code, or code built for either one of the more
restrictive FP32 or FP64. When linking with more restrictive code, the
overall requirement of the process becomes that of the more restrictive
code. The kernel has no way to know in advance which mode the process
will need to be executed in, and indeed it may need to change during
execution. The dynamic loader is the only code which will know the
overall required mode, and so it needs to have a means to instruct the
kernel to switch the FP mode of the process.

This patch introduces 2 new options to the prctl syscall which provide
such a capability. The FP mode of the process is represented as a
simple bitmask combining a number of mode bits mirroring those present
in the hardware. Userland can either retrieve the current FP mode of
the process:

  mode = prctl(PR_GET_FP_MODE);

or modify the current FP mode of the process:

  err = prctl(PR_SET_FP_MODE, new_mode);

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Matthew Fortune <matthew.fortune@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8899/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

3 files changed, 16 insertions, 0 deletions

diff --git a/arch/mips/include/asm/mmu.h b/arch/mips/include/asm/mmu.h
index c436138945a8..1afa1f986df8 100644
--- a/arch/mips/include/asm/mmu.h
+++ b/arch/mips/include/asm/mmu.h
@@ -1,9 +1,12 @@
 #ifndef __ASM_MMU_H
 #define __ASM_MMU_H
 
+#include <linux/atomic.h>
+
 typedef struct {
 	unsigned long asid[NR_CPUS];
 	void *vdso;
+	atomic_t fp_mode_switching;
 } mm_context_t;
 
 #endif /* __ASM_MMU_H */
diff --git a/arch/mips/include/asm/mmu_context.h b/arch/mips/include/asm/mmu_context.h
index 2f82568a3ee4..87f11072f557 100644
--- a/arch/mips/include/asm/mmu_context.h
+++ b/arch/mips/include/asm/mmu_context.h
@@ -132,6 +132,8 @@ init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 	for_each_possible_cpu(i)
 		cpu_context(i, mm) = 0;
 
+	atomic_set(&mm->context.fp_mode_switching, 0);
+
 	return 0;
 }
 
diff --git a/arch/mips/include/asm/processor.h b/arch/mips/include/asm/processor.h
index f1df4cb4a286..9daa38608cd8 100644
--- a/arch/mips/include/asm/processor.h
+++ b/arch/mips/include/asm/processor.h
@@ -399,4 +399,15 @@ unsigned long get_wchan(struct task_struct *p);
 
 #endif
 
+/*
+ * Functions & macros implementing the PR_GET_FP_MODE & PR_SET_FP_MODE options
+ * to the prctl syscall.
+ */
+extern int mips_get_process_fp_mode(struct task_struct *task);
+extern int mips_set_process_fp_mode(struct task_struct *task,
+				    unsigned int value);
+
+#define GET_FP_MODE(task)		mips_get_process_fp_mode(task)
+#define SET_FP_MODE(task,value)		mips_set_process_fp_mode(task, value)
+
 #endif /* _ASM_PROCESSOR_H */