RISC-V: vector: export VLENB csr in __sc_riscv_v_state

VLENB is critical for callers of ptrace to reconstruct Vector register
files from the register dump of NT_RISCV_VECTOR. Also, future systems
may will have a writable VLENB, so add it now to potentially save future
compatibility issue.

Fixes: 0c59922 ("riscv: Add ptrace vector support")
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20230816155450.26200-3-andy.chiu@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/vector.h

@@ -70,8 +70,9 @@ static __always_inline void __vstate_csr_save(struct __riscv_v_ext_state *dest)
 		"csrr	%1, " __stringify(CSR_VTYPE) "\n\t"
 		"csrr	%2, " __stringify(CSR_VL) "\n\t"
 		"csrr	%3, " __stringify(CSR_VCSR) "\n\t"
+		"csrr	%4, " __stringify(CSR_VLENB) "\n\t"
 		: "=r" (dest->vstart), "=r" (dest->vtype), "=r" (dest->vl),
-		  "=r" (dest->vcsr) : :);
+		  "=r" (dest->vcsr), "=r" (dest->vlenb) : :);
 }
 
 static __always_inline void __vstate_csr_restore(struct __riscv_v_ext_state *src)

arch/riscv/include/uapi/asm/ptrace.h

@@ -97,6 +97,7 @@ struct __riscv_v_ext_state {
 	unsigned long vl;
 	unsigned long vtype;
 	unsigned long vcsr;
+	unsigned long vlenb;
 	void *datap;
 	/*
 	 * In signal handler, datap will be set a correct user stack offset