1 files changed, 108 insertions, 1 deletions

diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
index 87c911f018..57491740d7 100644
--- a/target/arm/arm-semi.c
+++ b/target/arm/arm-semi.c
@@ -110,6 +110,7 @@ typedef enum GuestFDType {
     GuestFDUnused = 0,
     GuestFDHost = 1,
     GuestFDGDB = 2,
+    GuestFDFeatureFile = 3,
 } GuestFDType;
 
 /*
@@ -118,7 +119,10 @@ typedef enum GuestFDType {
  */
 typedef struct GuestFD {
     GuestFDType type;
-    int hostfd;
+    union {
+        int hostfd;
+        target_ulong featurefile_offset;
+    };
 } GuestFD;
 
 static GArray *guestfd_array;
@@ -504,6 +508,89 @@ static uint32_t gdb_flenfn(ARMCPU *cpu, GuestFD *gf)
                            gf->hostfd, arm_flen_buf(cpu));
 }
 
+#define SHFB_MAGIC_0 0x53
+#define SHFB_MAGIC_1 0x48
+#define SHFB_MAGIC_2 0x46
+#define SHFB_MAGIC_3 0x42
+
+static const uint8_t featurefile_data[] = {
+    SHFB_MAGIC_0,
+    SHFB_MAGIC_1,
+    SHFB_MAGIC_2,
+    SHFB_MAGIC_3,
+    0, /* Feature byte 0 */
+};
+
+static void init_featurefile_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = GuestFDFeatureFile;
+    gf->featurefile_offset = 0;
+}
+
+static uint32_t featurefile_closefn(ARMCPU *cpu, GuestFD *gf)
+{
+    /* Nothing to do */
+    return 0;
+}
+
+static uint32_t featurefile_writefn(ARMCPU *cpu, GuestFD *gf,
+                                    target_ulong buf, uint32_t len)
+{
+    /* This fd can never be open for writing */
+    CPUARMState *env = &cpu->env;
+
+    errno = EBADF;
+    return set_swi_errno(env, -1);
+}
+
+static uint32_t featurefile_readfn(ARMCPU *cpu, GuestFD *gf,
+                                   target_ulong buf, uint32_t len)
+{
+    uint32_t i;
+#ifndef CONFIG_USER_ONLY
+    CPUARMState *env = &cpu->env;
+#endif
+    char *s;
+
+    s = lock_user(VERIFY_WRITE, buf, len, 0);
+    if (!s) {
+        return len;
+    }
+
+    for (i = 0; i < len; i++) {
+        if (gf->featurefile_offset >= sizeof(featurefile_data)) {
+            break;
+        }
+        s[i] = featurefile_data[gf->featurefile_offset];
+        gf->featurefile_offset++;
+    }
+
+    unlock_user(s, buf, len);
+
+    /* Return number of bytes not read */
+    return len - i;
+}
+
+static uint32_t featurefile_isattyfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return 0;
+}
+
+static uint32_t featurefile_seekfn(ARMCPU *cpu, GuestFD *gf,
+                                   target_ulong offset)
+{
+    gf->featurefile_offset = offset;
+    return 0;
+}
+
+static uint32_t featurefile_flenfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return sizeof(featurefile_data);
+}
+
 typedef struct GuestFDFunctions {
     sys_closefn *closefn;
     sys_writefn *writefn;
@@ -530,6 +617,14 @@ static const GuestFDFunctions guestfd_fns[] = {
         .seekfn = gdb_seekfn,
         .flenfn = gdb_flenfn,
     },
+    [GuestFDFeatureFile] = {
+        .closefn = featurefile_closefn,
+        .writefn = featurefile_writefn,
+        .readfn = featurefile_readfn,
+        .isattyfn = featurefile_isattyfn,
+        .seekfn = featurefile_seekfn,
+        .flenfn = featurefile_flenfn,
+    },
 };
 
 /* Read the input value from the argument block; fail the semihosting
@@ -616,6 +711,18 @@ target_ulong do_arm_semihosting(CPUARMState *env)
             unlock_user(s, arg0, 0);
             return guestfd;
         }
+        if (strcmp(s, ":semihosting-features") == 0) {
+            unlock_user(s, arg0, 0);
+            /* We must fail opens for modes other than 0 ('r') or 1 ('rb') */
+            if (arg1 != 0 && arg1 != 1) {
+                dealloc_guestfd(guestfd);
+                errno = EACCES;
+                return set_swi_errno(env, -1);
+            }
+            init_featurefile_guestfd(guestfd);
+            return guestfd;
+        }
+
         if (use_gdb_syscalls()) {
             arm_semi_open_guestfd = guestfd;
             ret = arm_gdb_syscall(cpu, arm_semi_open_cb, "open,%s,%x,1a4", arg0,