feat(inc/hypercall): introduce arch-specific hypercall in/out convention

This commit introduces a separation of input and output conventions for
hypercalls, addressing architecture-specific differences between ARM
and RISC-V. On ARM, the x0 register is used to pass both the extid,
fid, and the return value, while additional parameters (hypercalls arguments)
are passed via registers x1 to xn. On RISC-V, while the return value is
passed in a0, the extid and fid are handled by the a7 and a6 registers,
respectively. This means that the hypercall input arguments on RISC-V
should be passed through registers a0 to a5, while output hypercall
arguments are passed via a2 and onward (because all registers except
a0 and a1 must be preserved across an SBI call by the callee).
To accommodate these differences and provide a uniform interface,
two macros were introduced to abstract the handling of input and output
hypercall arguments across architectures.

Signed-off-by: João Peixoto <[email protected]>

Author: joaopeixoto13

src/arch/armv8/inc/arch/hypercall.h

@@ -6,6 +6,7 @@
 #ifndef ARCH_HYPERCALL_H
 #define ARCH_HYPERCALL_H
 
-#define HYPCALL_ARG_REG(ARG) ((ARG) + 1)
+#define HYPCALL_IN_ARG_REG(ARG)  ((ARG) + 1)
+#define HYPCALL_OUT_ARG_REG(ARG) (HYPCALL_IN_ARG_REG(ARG))
 
 #endif /* ARCH_HYPERCALL_H */

src/arch/riscv/inc/arch/hypercall.h

@@ -6,6 +6,7 @@
 #ifndef ARCH_HYPERCALL_H
 #define ARCH_HYPERCALL_H
 
-#define HYPCALL_ARG_REG(ARG) ((ARG) + REG_A0)
+#define HYPCALL_IN_ARG_REG(ARG)  ((ARG) + REG_A0)
+#define HYPCALL_OUT_ARG_REG(ARG) (HYPCALL_IN_ARG_REG((ARG) + 2))
 
 #endif /* ARCH_HYPERCALL_H */

src/core/hypercall.c

@@ -12,9 +12,9 @@ long int hypercall(unsigned long id)
 {
     long int ret = -HC_E_INVAL_ID;
 
-    unsigned long arg0 = vcpu_readreg(cpu()->vcpu, HYPCALL_ARG_REG(0));
-    unsigned long arg1 = vcpu_readreg(cpu()->vcpu, HYPCALL_ARG_REG(1));
-    unsigned long arg2 = vcpu_readreg(cpu()->vcpu, HYPCALL_ARG_REG(2));
+    unsigned long arg0 = vcpu_readreg(cpu()->vcpu, HYPCALL_IN_ARG_REG(0));
+    unsigned long arg1 = vcpu_readreg(cpu()->vcpu, HYPCALL_IN_ARG_REG(1));
+    unsigned long arg2 = vcpu_readreg(cpu()->vcpu, HYPCALL_IN_ARG_REG(2));
 
     switch (id) {
         case HC_IPC: