[v3,3/3] capstone: Add s390x skipdata callback

Commit Message

Richard Henderson Oct. 15, 2019, 5:51 p.m. UTC

Capstone assumes any 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.

Signed-off-by: Richard Henderson <[e-mail]>
---
 disas.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

Comments

Thomas Huth Oct. 15, 2019, 6:46 p.m. UTC | #1

On 15/10/2019 19.51, Richard Henderson wrote:
> Capstone assumes any 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.
> 
> Signed-off-by: Richard Henderson <[e-mail]>
> ---
>  disas.c | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/disas.c b/disas.c
> index 51c71534a3..2a000cbeb0 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;
> +}

The kernel has also a nice function to calculate this:

static inline int insn_length(unsigned char code)
{
        return ((((int) code + 64) >> 7) + 1) << 1;
}

... but the switch-case is likely easier to read, so anyway:

Reviewed-by: Thomas Huth <[e-mail]>

Richard Henderson Oct. 15, 2019, 7:22 p.m. UTC | #2

On 10/15/19 11:46 AM, Thomas Huth wrote:
>> +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;
>> +}
> 
> The kernel has also a nice function to calculate this:
> 
> static inline int insn_length(unsigned char code)
> {
>         return ((((int) code + 64) >> 7) + 1) << 1;
> }
> 
> ... but the switch-case is likely easier to read, so anyway:

Clever.

I don't mind swapping to the kernel version, so long as we convert the
target/s390x/internal.h function as well.


r~

Patch

diff --git a/disas.c b/disas.c
index 51c71534a3..2a000cbeb0 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) {