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 a1 and onward.
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) + 1))
 
 #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: