[RFC PATCH 6/6] riscv: add floating point insn support to misaligned access emulation
From: Clément Léger
Date: Sat Jun 24 2023 - 08:21:28 EST
This support is partially based of openSBI misaligned emulation floating
point instruction support. It provides support for the existing
floating point instructions (both for 32/64 bits as well as compressed
ones). Since floating point registers are not aprt of the pt_regs
struct, we need to modify them directly using some assembly. We also
dirty the pt_regs status in case we modify them to be sure context
switch will save them. With this support, Linux is on par with openSBI
support.
Signed-off-by: Clément Léger <cleger@xxxxxxxxxxxx>
---
arch/riscv/kernel/fpu.S | 118 ++++++++++++++++++++++++
arch/riscv/kernel/traps_misaligned.c | 130 ++++++++++++++++++++++++++-
2 files changed, 244 insertions(+), 4 deletions(-)
diff --git a/arch/riscv/kernel/fpu.S b/arch/riscv/kernel/fpu.S
index dd2205473de7..27f2e35ce8c2 100644
--- a/arch/riscv/kernel/fpu.S
+++ b/arch/riscv/kernel/fpu.S
@@ -104,3 +104,121 @@ ENTRY(__fstate_restore)
csrc CSR_STATUS, t1
ret
ENDPROC(__fstate_restore)
+
+
+#define get_f32(which) fmv.x.s a0, which; j 2f
+#define put_f32(which) fmv.s.x which, a1; j 2f
+#if __riscv_xlen == 64
+# define get_f64(which) fmv.x.d a0, which; j 2f
+# define put_f64(which) fmv.d.x which, a1; j 2f
+#else
+# define get_f64(which) fsd which, 0(a1); j 2f
+# define put_f64(which) fld which, 0(a1); j 2f
+#endif
+
+.macro fp_access_prologue
+ /*
+ * Compute jump offset to store the correct FP register since we don't
+ * have indirect FP register access
+ */
+ sll t0, a0, 3
+ la t2, 1f
+ add t0, t0, t2
+ li t1, SR_FS
+ csrs CSR_STATUS, t1
+ jr t0
+1:
+.endm
+
+.macro fp_access_epilogue
+2:
+ csrc CSR_STATUS, t1
+ ret
+.endm
+
+#define fp_access_body(__access_func) \
+ __access_func(f0); \
+ __access_func(f1); \
+ __access_func(f2); \
+ __access_func(f3); \
+ __access_func(f4); \
+ __access_func(f5); \
+ __access_func(f6); \
+ __access_func(f7); \
+ __access_func(f8); \
+ __access_func(f9); \
+ __access_func(f10); \
+ __access_func(f11); \
+ __access_func(f12); \
+ __access_func(f13); \
+ __access_func(f14); \
+ __access_func(f15); \
+ __access_func(f16); \
+ __access_func(f17); \
+ __access_func(f18); \
+ __access_func(f19); \
+ __access_func(f20); \
+ __access_func(f21); \
+ __access_func(f22); \
+ __access_func(f23); \
+ __access_func(f24); \
+ __access_func(f25); \
+ __access_func(f26); \
+ __access_func(f27); \
+ __access_func(f28); \
+ __access_func(f29); \
+ __access_func(f30); \
+ __access_func(f31)
+
+
+/*
+ * Disable compressed instructions set to keep a constant offset between FP
+ * load/store/move instructions
+ */
+.option norvc
+/*
+ * put_f32_reg - Set a FP register from a register containing the value
+ * a0 = FP register index to be set
+ * a1 = value to be loaded in the FP register
+ */
+SYM_FUNC_START(put_f32_reg)
+ fp_access_prologue
+ fp_access_body(put_f32)
+ fp_access_epilogue
+SYM_FUNC_END(put_f32_reg)
+
+/*
+ * get_f32_reg - Get a FP register value and return it
+ * a0 = FP register index to be retrieved
+ */
+SYM_FUNC_START(get_f32_reg)
+ fp_access_prologue
+ fp_access_body(get_f32)
+ fp_access_epilogue
+SYM_FUNC_END(put_f32_reg)
+
+/*
+ * put_f64_reg - Set a 64 bits FP register from a value or a pointer.
+ * a0 = FP register index to be set
+ * a1 = value/pointer to be loaded in the FP register (when xlen == 32 bits, we
+ * load the value to a pointer).
+ */
+SYM_FUNC_START(put_f64_reg)
+ fp_access_prologue
+ fp_access_body(put_f64)
+ fp_access_epilogue
+SYM_FUNC_END(put_f64_reg)
+
+/*
+ * put_f64_reg - Get a 64 bits FP register value and returned it or store it to
+ * a pointer.
+ * a0 = FP register index to be retrieved
+ * a1 = If xlen == 32, pointer which should be loaded with the FP register value
+ * or unused if xlen == 64. In which case the FP register value is returned
+ * through a0
+ */
+SYM_FUNC_START(get_f64_reg)
+ fp_access_prologue
+ fp_access_body(get_f64)
+ fp_access_epilogue
+SYM_FUNC_END(get_f64_reg)
diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index b828a0f3d4f7..0c02d6ef6a85 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -153,6 +153,93 @@
#define PRECISION_S 0
#define PRECISION_D 1
+#ifdef CONFIG_FPU
+
+#define FP_GET_RD(insn) (insn >> 7 & 0x1F)
+
+extern void put_f32_reg(unsigned long fp_reg, unsigned long value);
+
+static inline void set_f32_rd(unsigned long insn, struct pt_regs *regs,
+ unsigned long val)
+{
+ unsigned long fp_reg = FP_GET_RD(insn);
+
+ put_f32_reg(fp_reg, val);
+ regs->status |= SR_FS_DIRTY;
+}
+
+extern void put_f64_reg(unsigned long fp_reg, unsigned long value);
+
+static inline void set_f64_rd(unsigned long insn, struct pt_regs *regs, u64 val)
+{
+ unsigned long fp_reg = FP_GET_RD(insn);
+ unsigned long value;
+
+#if __riscv_xlen == 32
+ value = (unsigned long) &val;
+#else
+ value = val;
+#endif
+ put_f64_reg(fp_reg, value);
+ regs->status |= SR_FS_DIRTY;
+}
+
+#if __riscv_xlen == 32
+extern void get_f64_reg(unsigned long fp_reg, u64 *value);
+
+static u64 get_f64_rs(unsigned long insn, u8 fp_reg_offset,
+ struct pt_regs *regs)
+{
+ unsigned long fp_reg = (insn >> fp_reg_offset) & 0x1F;
+ u64 val;
+
+ get_f64_reg(fp_reg, &val);
+ regs->status |= SR_FS_DIRTY;
+
+ return val;
+}
+#else
+
+extern unsigned long get_f64_reg(unsigned long fp_reg);
+
+static unsigned long get_f64_rs(unsigned long insn, u8 fp_reg_offset,
+ struct pt_regs *regs)
+{
+ unsigned long fp_reg = (insn >> fp_reg_offset) & 0x1F;
+ unsigned long val;
+
+ val = get_f64_reg(fp_reg);
+ regs->status |= SR_FS_DIRTY;
+
+ return val;
+}
+
+#endif
+
+#define GET_F64_RS2(insn, regs) (get_f64_rs(insn, 20, regs))
+#define GET_F64_RS2C(insn, regs) (get_f64_rs(insn, 2, regs))
+#define GET_F64_RS2S(insn, regs) (get_f64_rs(RVC_RS2S(insn), 0, regs))
+
+extern unsigned long get_f32_reg(unsigned long fp_reg);
+
+static unsigned long get_f32_rs(unsigned long insn, u8 fp_reg_offset,
+ struct pt_regs *regs)
+{
+ unsigned long fp_reg = (insn >> fp_reg_offset) & 0x1F;
+ unsigned long val;
+
+ val = get_f32_reg(fp_reg);
+ regs->status |= SR_FS_DIRTY;
+
+ return val;
+}
+
+#define GET_F32_RS2(insn, regs) (get_f32_rs(insn, 20, regs))
+#define GET_F32_RS2C(insn, regs) (get_f32_rs(insn, 2, regs))
+#define GET_F32_RS2S(insn, regs) (get_f32_rs(RVC_RS2S(insn), 0, regs))
+
+#endif
+
#ifdef CONFIG_RISCV_M_MODE
static inline int load_u8(const u8 *addr, u8 *r_val)
{
@@ -347,15 +434,21 @@ int handle_misaligned_load(struct pt_regs *regs)
return -1;
}
+ if (!IS_ENABLED(CONFIG_FPU) && fp)
+ return -1;
+
val.data_u64 = 0;
for (i = 0; i < len; i++) {
if (load_u8((void *)(addr + i), &val.data_bytes[i]))
return -1;
}
- if (fp)
- return -1;
- SET_RD(insn, regs, val.data_ulong << shift >> shift);
+ if (!fp)
+ SET_RD(insn, regs, val.data_ulong << shift >> shift);
+ else if (len == 8)
+ set_f64_rd(insn, regs, val.data_u64);
+ else
+ set_f32_rd(insn, regs, val.data_ulong);
regs->epc = epc + INSN_LEN(insn);
@@ -368,7 +461,7 @@ int handle_misaligned_store(struct pt_regs *regs)
unsigned long epc = regs->epc;
unsigned long insn;
unsigned long addr;
- int i, len = 0;
+ int i, len = 0, fp = 0;
/*
* When running in supervisor mode, we only handle misaligned accesses
@@ -394,6 +487,14 @@ int handle_misaligned_store(struct pt_regs *regs)
} else if ((insn & INSN_MASK_SD) == INSN_MATCH_SD) {
len = 8;
#endif
+ } else if ((insn & INSN_MASK_FSD) == INSN_MATCH_FSD) {
+ fp = 1;
+ len = 8;
+ val.data_u64 = GET_F64_RS2(insn, regs);
+ } else if ((insn & INSN_MASK_FSW) == INSN_MATCH_FSW) {
+ fp = 1;
+ len = 4;
+ val.data_ulong = GET_F32_RS2(insn, regs);
} else if ((insn & INSN_MASK_SH) == INSN_MATCH_SH) {
len = 2;
#if defined(CONFIG_64BIT)
@@ -412,11 +513,32 @@ int handle_misaligned_store(struct pt_regs *regs)
((insn >> SH_RD) & 0x1f)) {
len = 4;
val.data_ulong = GET_RS2C(insn, regs);
+ } else if ((insn & INSN_MASK_C_FSD) == INSN_MATCH_C_FSD) {
+ fp = 1;
+ len = 8;
+ val.data_u64 = GET_F64_RS2S(insn, regs);
+ } else if ((insn & INSN_MASK_C_FSDSP) == INSN_MATCH_C_FSDSP) {
+ fp = 1;
+ len = 8;
+ val.data_u64 = GET_F64_RS2C(insn, regs);
+#if !defined(CONFIG_64BIT)
+ } else if ((insn & INSN_MASK_C_FSW) == INSN_MATCH_C_FSW) {
+ fp = 1;
+ len = 4;
+ val.data_ulong = GET_F32_RS2S(insn, regs);
+ } else if ((insn & INSN_MASK_C_FSWSP) == INSN_MATCH_C_FSWSP) {
+ fp = 1;
+ len = 4;
+ val.data_ulong = GET_F32_RS2C(insn, regs);
+#endif
} else {
regs->epc = epc;
return -1;
}
+ if (!IS_ENABLED(CONFIG_FPU) && fp)
+ return -1;
+
for (i = 0; i < len; i++) {
if (store_u8((void *)(addr + i), val.data_bytes[i]))
return -1;
--
2.40.1