From 44e92e0364adfd7b6759084e02a550d06336d896 Mon Sep 17 00:00:00 2001 From: Vincent Chen Date: Thu, 22 Nov 2018 11:14:36 +0800 Subject: nds32: support denormalized result through FP emulator Currently, the nds32 FPU dose not support the arithmetic of denormalized number. When the nds32 FPU finds the result of the instruction is a denormlized number, the nds32 FPU considers it to be an underflow condition and rounds the result to an appropriate number. It may causes some loss of precision. This commit proposes a solution to re-execute the instruction by the FPU emulator to enhance the precision. To transfer calculations from user space to kernel space, this feature will enable the underflow exception trap by default. Enabling this feature may cause some side effects: 1. Performance loss due to extra FPU exception 2. Need another scheme to control real underflow trap A new parameter, UDF_trap, which is belong to FPU context is used to control underflow trap. User can configure this feature via CONFIG_SUPPORT_DENORMAL_ARITHMETIC Signed-off-by: Vincent Chen Acked-by: Greentime Hu Signed-off-by: Greentime Hu --- arch/nds32/include/uapi/asm/auxvec.h | 7 +++++++ arch/nds32/include/uapi/asm/sigcontext.h | 9 +++++++++ arch/nds32/include/uapi/asm/udftrap.h | 13 +++++++++++++ arch/nds32/include/uapi/asm/unistd.h | 2 ++ 4 files changed, 31 insertions(+) create mode 100644 arch/nds32/include/uapi/asm/udftrap.h (limited to 'arch/nds32/include/uapi/asm') diff --git a/arch/nds32/include/uapi/asm/auxvec.h b/arch/nds32/include/uapi/asm/auxvec.h index 56043ce4972f..2d3213f5e595 100644 --- a/arch/nds32/include/uapi/asm/auxvec.h +++ b/arch/nds32/include/uapi/asm/auxvec.h @@ -4,6 +4,13 @@ #ifndef __ASM_AUXVEC_H #define __ASM_AUXVEC_H +/* + * This entry gives some information about the FPU initialization + * performed by the kernel. + */ +#define AT_FPUCW 18 /* Used FPU control word. */ + + /* VDSO location */ #define AT_SYSINFO_EHDR 33 diff --git a/arch/nds32/include/uapi/asm/sigcontext.h b/arch/nds32/include/uapi/asm/sigcontext.h index 1257a78e3ae1..58afc416473e 100644 --- a/arch/nds32/include/uapi/asm/sigcontext.h +++ b/arch/nds32/include/uapi/asm/sigcontext.h @@ -12,6 +12,15 @@ struct fpu_struct { unsigned long long fd_regs[32]; unsigned long fpcsr; + /* + * UDF_trap is used to recognize whether underflow trap is enabled + * or not. When UDF_trap == 1, this process will be traped and then + * get a SIGFPE signal when encountering an underflow exception. + * UDF_trap is only modified through setfputrap syscall. Therefore, + * UDF_trap needn't be saved or loaded to context in each context + * switch. + */ + unsigned long UDF_trap; }; struct zol_struct { diff --git a/arch/nds32/include/uapi/asm/udftrap.h b/arch/nds32/include/uapi/asm/udftrap.h new file mode 100644 index 000000000000..433f79d679c0 --- /dev/null +++ b/arch/nds32/include/uapi/asm/udftrap.h @@ -0,0 +1,13 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) 2005-2018 Andes Technology Corporation */ +#ifndef _ASM_SETFPUTRAP +#define _ASM_SETFPUTRAP + +/* + * Options for setfputrap system call + */ +#define DISABLE_UDFTRAP 0 /* disable underflow exception trap */ +#define ENABLE_UDFTRAP 1 /* enable undeflos exception trap */ +#define GET_UDFTRAP 2 /* only get undeflos exception trap status */ + +#endif /* _ASM_CACHECTL */ diff --git a/arch/nds32/include/uapi/asm/unistd.h b/arch/nds32/include/uapi/asm/unistd.h index 603e826e0449..c2c3a3e34083 100644 --- a/arch/nds32/include/uapi/asm/unistd.h +++ b/arch/nds32/include/uapi/asm/unistd.h @@ -9,4 +9,6 @@ /* Additional NDS32 specific syscalls. */ #define __NR_cacheflush (__NR_arch_specific_syscall) +#define __NR_udftrap (__NR_arch_specific_syscall + 1) __SYSCALL(__NR_cacheflush, sys_cacheflush) +__SYSCALL(__NR_udftrap, sys_udftrap) -- cgit v1.2.3