The integrated assembler of Clang 10 and earlier do not allow to access
the VFP registers through the coprocessor load/store instructions:
arch/arm/vfp/vfpmodule.c:342:2: error: invalid operand for instruction
fmxr(FPEXC, fpexc &
~(FPEXC_EX|FPEXC_DEX|FPEXC_FP2V|FPEXC_VV|FPEXC_TRAP_MASK));
^
arch/arm/vfp/vfpinstr.h:79:6: note: expanded from macro 'fmxr'
asm("mcr p10, 7, %0, " vfpreg(_vfp_) ", cr0, 0 @ fmxr " #_vfp_ ", %0"
\
^
<inline asm>:1:6: note: instantiated into assembly here
mcr p10, 7, r0, cr8, cr0, 0 @ fmxr FPEXC, r0
^
This has been addressed with Clang 11 [0]. However, to support earlier
versions of Clang and for better readability use of VFP assembler
mnemonics still is preferred.
Ideally we would replace this code with the unified assembler language
mnemonics vmrs/vmsr on call sites along with .fpu assembler directives.
The GNU assembler supports the .fpu directive at least since 2.17 (when
documentation has been added). Since Linux requires binutils 2.21 it is
safe to use .fpu directive. However, binutils does not allow to use
FPINST or FPINST2 as an argument to vmrs/vmsr instructions up to
binutils 2.24 (see binutils commit 16d02dc907c5):
arch/arm/vfp/vfphw.S: Assembler messages:
arch/arm/vfp/vfphw.S:162: Error: operand 0 must be FPSID or FPSCR pr FPEXC --
`vmsr FPINST,r6'
arch/arm/vfp/vfphw.S:165: Error: operand 0 must be FPSID or FPSCR pr FPEXC --
`vmsr FPINST2,r8'
arch/arm/vfp/vfphw.S:235: Error: operand 1 must be a VFP extension System
Register -- `vmrs r3,FPINST'
arch/arm/vfp/vfphw.S:238: Error: operand 1 must be a VFP extension System
Register -- `vmrs r12,FPINST2'
Use as-instr in Kconfig to check if FPINST/FPINST2 can be used. If they
can be used make use of .fpu directives and UAL VFP mnemonics for
register access.
This allows to build vfpmodule.c with Clang and its integrated assembler.
[0] https://reviews.llvm.org/D59733
Link: https://github.com/ClangBuiltLinux/linux/issues/905
Signed-off-by: Stefan Agner <ste...@agner.ch>
---
Changes in v3:
- Reworded commit message, adding hint that Clang 11 won't have this
restriction any longer
Changes in v2:
- Check assembler capabilities in Kconfig instead of Makefile
arch/arm/Kconfig | 2 ++
arch/arm/Kconfig.assembler | 6 ++++++
arch/arm/include/asm/vfp.h | 2 ++
arch/arm/include/asm/vfpmacros.h | 12 +++++++++++-
arch/arm/vfp/vfphw.S | 1 +
arch/arm/vfp/vfpinstr.h | 23 +++++++++++++++++++----
6 files changed, 41 insertions(+), 5 deletions(-)
create mode 100644 arch/arm/Kconfig.assembler
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 2ac74904a3ce..911f55a11c63 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -2097,3 +2097,5 @@ source "drivers/firmware/Kconfig"
if CRYPTO
source "arch/arm/crypto/Kconfig"
endif
+
+source "arch/arm/Kconfig.assembler"
diff --git a/arch/arm/Kconfig.assembler b/arch/arm/Kconfig.assembler
new file mode 100644
index 000000000000..5cb31aae1188
--- /dev/null
+++ b/arch/arm/Kconfig.assembler
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config AS_VFP_VMRS_FPINST
+ def_bool $(as-instr,.fpu vfpv2\nvmrs r0$(comma)FPINST)
+ help
+ Supported by binutils >= 2.24 and LLVM integrated assembler.
diff --git a/arch/arm/include/asm/vfp.h b/arch/arm/include/asm/vfp.h
index 7157d2a30a49..19928bfb4f9c 100644
--- a/arch/arm/include/asm/vfp.h
+++ b/arch/arm/include/asm/vfp.h
@@ -9,6 +9,7 @@
#ifndef __ASM_VFP_H
#define __ASM_VFP_H
+#ifndef CONFIG_AS_VFP_VMRS_FPINST
#define FPSID cr0
#define FPSCR cr1
#define MVFR1 cr6
@@ -16,6 +17,7 @@
#define FPEXC cr8
#define FPINST cr9
#define FPINST2 cr10
+#endif
/* FPSID bits */
#define FPSID_IMPLEMENTER_BIT (24)
diff --git a/arch/arm/include/asm/vfpmacros.h b/arch/arm/include/asm/vfpmacros.h
index 947ee5395e1f..ba0d4cb5377e 100644
--- a/arch/arm/include/asm/vfpmacros.h
+++ b/arch/arm/include/asm/vfpmacros.h
@@ -8,7 +8,16 @@
#include <asm/vfp.h>
-@ Macros to allow building with old toolkits (with no VFP support)
+#ifdef CONFIG_AS_VFP_VMRS_FPINST
+ .macro VFPFMRX, rd, sysreg, cond
+ vmrs\cond \rd, \sysreg
+ .endm
+
+ .macro VFPFMXR, sysreg, rd, cond
+ vmsr\cond \sysreg, \rd
+ .endm
+#else
+ @ Macros to allow building with old toolkits (with no VFP support)
.macro VFPFMRX, rd, sysreg, cond
MRC\cond p10, 7, \rd, \sysreg, cr0, 0 @ FMRX \rd, \sysreg
.endm
@@ -16,6 +25,7 @@
.macro VFPFMXR, sysreg, rd, cond
MCR\cond p10, 7, \rd, \sysreg, cr0, 0 @ FMXR \sysreg, \rd
.endm
+#endif
@ read all the working registers back into the VFP
.macro VFPFLDMIA, base, tmp
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index 29ed36b99d1d..4fcff9f59947 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -78,6 +78,7 @@
ENTRY(vfp_support_entry)
DBGSTR3 "instr %08x pc %08x state %p", r0, r2, r10
+ .fpu vfpv2
ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions
and r3, r3, #MODE_MASK @ are supported in kernel mode
teq r3, #USR_MODE
diff --git a/arch/arm/vfp/vfpinstr.h b/arch/arm/vfp/vfpinstr.h
index 38dc154e39ff..3c7938fd40aa 100644
--- a/arch/arm/vfp/vfpinstr.h
+++ b/arch/arm/vfp/vfpinstr.h
@@ -62,10 +62,23 @@
#define FPSCR_C (1 << 29)
#define FPSCR_V (1 << 28)
-/*
- * Since we aren't building with -mfpu=vfp, we need to code
- * these instructions using their MRC/MCR equivalents.
- */
+#ifdef CONFIG_AS_VFP_VMRS_FPINST
+
+#define fmrx(_vfp_) ({ \
+ u32 __v; \
+ asm(".fpu vfpv2\n" \
+ "vmrs %0, " #_vfp_ \
+ : "=r" (__v) : : "cc"); \
+ __v; \
+ })
+
+#define fmxr(_vfp_,_var_) \
+ asm(".fpu vfpv2\n" \
+ "vmsr " #_vfp_ ", %0" \
+ : : "r" (_var_) : "cc")
+
+#else
+
#define vfpreg(_vfp_) #_vfp_
#define fmrx(_vfp_) ({ \
@@ -79,6 +92,8 @@
asm("mcr p10, 7, %0, " vfpreg(_vfp_) ", cr0, 0 @ fmxr " #_vfp_ ", %0"
\
: : "r" (_var_) : "cc")
+#endif
+
u32 vfp_single_cpdo(u32 inst, u32 fpscr);
u32 vfp_single_cprt(u32 inst, u32 fpscr, struct pt_regs *regs);
--
2.27.0
