[Xen-devel] [PATCH 06/14] fuzz/x86_emulate: Implement dread() and davail()

[George Dunlap <george.dunlap@xxxxxxxxxx>]

Rather than open-coding the "read" from the input file.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---
CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
---
 tools/fuzz/x86_instruction_emulator/fuzz-emul.c | 31 ++++++++++++++++++-------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/tools/fuzz/x86_instruction_emulator/fuzz-emul.c 
b/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
index 7f9a369421..0f5ff0b265 100644
--- a/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
+++ b/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
@@ -52,6 +52,22 @@ struct fuzz_state
     struct x86_emulate_ops ops;
 };
 
+static inline int davail(struct fuzz_state *s, size_t size)
+{
+    return s->data_index + size < s->data_num;
+}
+
+static inline int dread(struct fuzz_state *s, void *dst, size_t size)
+{
+    if ( !davail(s, size) )
+        return 0;
+
+    memcpy(dst, &s->corpus->data[s->data_index], size);
+    s->data_index += size;
+
+    return 1;
+}
+
 char *x86emul_return_string[] = {
     [X86EMUL_OKAY]="X86EMUL_OKAY",
     [X86EMUL_UNHANDLEABLE]="X86EMUL_UNHANDLEABLE",
@@ -68,10 +84,10 @@ static int maybe_fail(struct x86_emulate_ctxt *ctxt,
                       const char *why, bool exception)
 {
     struct fuzz_state *s = ctxt->data;
-    const struct fuzz_corpus *c = s->corpus;
+    unsigned char c;
     int rc;
 
-    if ( s->data_index >= s->data_num )
+    if ( !dread(s, &c, sizeof(c)) )
         rc = X86EMUL_EXCEPTION;
     else
     {
@@ -80,13 +96,12 @@ static int maybe_fail(struct x86_emulate_ctxt *ctxt,
          * 25% unhandlable
          * 25% exception
          */
-        if ( c->data[s->data_index] > 0xc0 )
+        if ( c > 0xc0 )
             rc = X86EMUL_EXCEPTION;
-        else if ( c->data[s->data_index] > 0x80 )
+        else if ( c > 0x80 )
             rc = X86EMUL_UNHANDLEABLE;
         else
             rc = X86EMUL_OKAY;
-        s->data_index++;
     }
 
     if ( rc == X86EMUL_EXCEPTION && !exception )
@@ -106,11 +121,10 @@ static int data_read(struct x86_emulate_ctxt *ctxt,
                      const char *why, void *dst, unsigned int bytes)
 {
     struct fuzz_state *s = ctxt->data;
-    const struct fuzz_corpus *c = s->corpus;
     unsigned int i;
     int rc;
 
-    if ( s->data_index + bytes > s->data_num )
+    if ( !davail(s, bytes) )
     {
         /*
          * Fake up a segment limit violation.  System segment limit volations
@@ -128,8 +142,7 @@ static int data_read(struct x86_emulate_ctxt *ctxt,
 
     if ( rc == X86EMUL_OKAY )
     {
-        memcpy(dst, &c->data[s->data_index], bytes);
-        s->data_index += bytes;
+        dread(s, dst, bytes);
 
         printf("%s: ", why);
         for ( i = 0; i < bytes; i++ )
-- 
2.14.1


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