[Qemu-devel] [PATCH 12/13] target/arm/arm-semi: Implement SH_EXT_STDOUT_STDERR extension

[Peter Maydell]

SH_EXT_STDOUT_STDERR is a v2.0 semihosting extension: the guest
can open ":tt" with a file mode requesting append access in
order to open stderr, in addition to the existing "open for
read for stdin or write for stdout". Implement this and
report it via the :semihosting-features data.

Signed-off-by: Peter Maydell <address@hidden>
---
 target/arm/arm-semi.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
index 531084b7799..0df8d4d69d6 100644
--- a/target/arm/arm-semi.c
+++ b/target/arm/arm-semi.c
@@ -476,12 +476,16 @@ static uint32_t gdb_flenfn(TaskState *ts, ARMCPU *cpu, 
GuestFD *gf)
 #define SHFB_MAGIC_2 0x46
 #define SHFB_MAGIC_3 0x42
 
+/* Feature bits reportable in feature byte 0 */
+#define SH_EXT_EXIT_EXTENDED (1 << 0)
+#define SH_EXT_STDOUT_STDERR (1 << 1)
+
 static const uint8_t featurefile_data[] = {
     SHFB_MAGIC_0,
     SHFB_MAGIC_1,
     SHFB_MAGIC_2,
     SHFB_MAGIC_3,
-    0, /* Feature byte 0 */
+    SH_EXT_STDOUT_STDERR, /* Feature byte 0 */
 };
 
 static void init_featurefile_guestfd(int guestfd)
@@ -674,7 +678,21 @@ target_ulong do_arm_semihosting(CPUARMState *env)
         }
 
         if (strcmp(s, ":tt") == 0) {
-            int result_fileno = arg1 < 4 ? STDIN_FILENO : STDOUT_FILENO;
+            int result_fileno;
+
+            /*
+             * We implement SH_EXT_STDOUT_STDERR, so:
+             *  open for read == stdin
+             *  open for write == stdout
+             *  open for append == stderr
+             */
+            if (arg1 < 4) {
+                result_fileno = STDIN_FILENO;
+            } else if (arg1 < 8) {
+                result_fileno = STDOUT_FILENO;
+            } else {
+                result_fileno = STDERR_FILENO;
+            }
             associate_guestfd(guestfd, result_fileno);
             unlock_user(s, arg0, 0);
             return guestfd;
-- 
2.20.1