target/arm/arm-semi: Factor out implementation of SYS_CLOSE

Currently for the semihosting calls which take a file descriptor
(SYS_CLOSE, SYS_WRITE, SYS_READ, SYS_ISTTY, SYS_SEEK, SYS_FLEN)
we have effectively two implementations, one for real host files
and one for when we indirect via the gdbstub. We want to add a
third one to deal with the magic :semihosting-features file.

Instead of having a three-way if statement in each of these
cases, factor out the implementation of the calls to separate
functions which we dispatch to via function pointers selected
via the GuestFDType for the guest fd.

In this commit, we set up the framework for the dispatch,
and convert the SYS_CLOSE call to use it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190916141544.17540-8-peter.maydell@linaro.org

target/arm/arm-semi.c

@@ -109,6 +109,7 @@ static int open_modeflags[12] = {
 typedef enum GuestFDType {
     GuestFDUnused = 0,
     GuestFDHost = 1,
+    GuestFDGDB = 2,
 } GuestFDType;
 
 /*
@@ -172,14 +173,14 @@ static GuestFD *do_get_guestfd(int guestfd)
 /*
  * Associate the specified guest fd (which must have been
  * allocated via alloc_fd() and not previously used) with
- * the specified host fd.
+ * the specified host/gdb fd.
  */
 static void associate_guestfd(int guestfd, int hostfd)
 {
     GuestFD *gf = do_get_guestfd(guestfd);
 
     assert(gf);
-    gf->type = GuestFDHost;
+    gf->type = use_gdb_syscalls() ? GuestFDGDB : GuestFDHost;
     gf->hostfd = hostfd;
 }
 
@@ -376,6 +377,39 @@ static target_ulong arm_gdb_syscall(ARMCPU *cpu, gdb_syscall_complete_cb cb,
     return is_a64(env) ? env->xregs[0] : env->regs[0];
 }
 
+/*
+ * Types for functions implementing various semihosting calls
+ * for specific types of guest file descriptor. These must all
+ * do the work and return the required return value for the guest,
+ * setting the guest errno if appropriate.
+ */
+typedef uint32_t sys_closefn(ARMCPU *cpu, GuestFD *gf);
+
+static uint32_t host_closefn(ARMCPU *cpu, GuestFD *gf)
+{
+    CPUARMState *env = &cpu->env;
+
+    return set_swi_errno(env, close(gf->hostfd));
+}
+
+static uint32_t gdb_closefn(ARMCPU *cpu, GuestFD *gf)
+{
+    return arm_gdb_syscall(cpu, arm_semi_cb, "close,%x", gf->hostfd);
+}
+
+typedef struct GuestFDFunctions {
+    sys_closefn *closefn;
+} GuestFDFunctions;
+
+static const GuestFDFunctions guestfd_fns[] = {
+    [GuestFDHost] = {
+        .closefn = host_closefn,
+    },
+    [GuestFDGDB] = {
+        .closefn = gdb_closefn,
+    },
+};
+
 /* Read the input value from the argument block; fail the semihosting
  * call if the memory read fails.
  */
@@ -485,11 +519,7 @@ target_ulong do_arm_semihosting(CPUARMState *env)
             return set_swi_errno(env, -1);
         }
 
-        if (use_gdb_syscalls()) {
-            ret = arm_gdb_syscall(cpu, arm_semi_cb, "close,%x", gf->hostfd);
-        } else {
-            ret = set_swi_errno(env, close(gf->hostfd));
-        }
+        ret = guestfd_fns[gf->type].closefn(cpu, gf);
         dealloc_guestfd(arg0);
         return ret;
     case TARGET_SYS_WRITEC: