[PULL 3/3] capstone: Add skipdata hook for s390x

[Richard Henderson <richard.henderson@linaro.org>]

Capstone assumes any s390x unknown instruction is 2 bytes.
Instead, use the ilen field in the first two bits of
the instruction to stay in sync with the insn stream.

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 disas.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/disas.c b/disas.c
index 845c40fca8..1095bad049 100644
--- a/disas.c
+++ b/disas.c
@@ -178,6 +178,39 @@ static int print_insn_od_target(bfd_vma pc, disassemble_info *info)
    to share this across calls and across host vs target disassembly.  */
 static __thread cs_insn *cap_insn;
 
+/*
+ * The capstone library always skips 2 bytes for S390X.
+ * This is less than ideal, since we can tell from the first two bits
+ * the size of the insn and thus stay in sync with the insn stream.
+ */
+static size_t CAPSTONE_API
+cap_skipdata_s390x_cb(const uint8_t *code, size_t code_size,
+                      size_t offset, void *user_data)
+{
+    size_t ilen;
+
+    /* See get_ilen() in target/s390x/internal.h.  */
+    switch (code[offset] >> 6) {
+    case 0:
+        ilen = 2;
+        break;
+    case 1:
+    case 2:
+        ilen = 4;
+        break;
+    default:
+        ilen = 6;
+        break;
+    }
+
+    return ilen;
+}
+
+static const cs_opt_skipdata cap_skipdata_s390x = {
+    .mnemonic = ".byte",
+    .callback = cap_skipdata_s390x_cb
+};
+
 /* Initialize the Capstone library.  */
 /* ??? It would be nice to cache this.  We would need one handle for the
    host and one for the target.  For most targets we can reset specific
@@ -208,6 +241,10 @@ static cs_err cap_disas_start(disassemble_info *info, csh *handle)
 
     /* "Disassemble" unknown insns as ".byte W,X,Y,Z".  */
     cs_option(*handle, CS_OPT_SKIPDATA, CS_OPT_ON);
+    if (info->cap_arch == CS_ARCH_SYSZ) {
+        cs_option(*handle, CS_OPT_SKIPDATA_SETUP,
+                  (uintptr_t)&cap_skipdata_s390x);
+    }
 
     /* Allocate temp space for cs_disasm_iter.  */
     if (cap_insn == NULL) {
-- 
2.20.1