disas: use result of ->read_memory_func

This gets especially confusing if you start plugging in host addresses
from a trace and you wonder why the output keeps changing. Report when
read_memory_func fails instead of blindly disassembling the buffer
contents.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220929114231.583801-35-alex.bennee@linaro.org>

disas.c

@@ -83,18 +83,18 @@ static int print_insn_objdump(bfd_vma pc, disassemble_info *info,
                               const char *prefix)
 {
     int i, n = info->buffer_length;
-    uint8_t *buf = g_malloc(n);
-
-    info->read_memory_func(pc, buf, n, info);
-
-    for (i = 0; i < n; ++i) {
-        if (i % 32 == 0) {
-            info->fprintf_func(info->stream, "\n%s: ", prefix);
+    g_autofree uint8_t *buf = g_malloc(n);
+
+    if (info->read_memory_func(pc, buf, n, info) == 0) {
+        for (i = 0; i < n; ++i) {
+            if (i % 32 == 0) {
+                info->fprintf_func(info->stream, "\n%s: ", prefix);
+            }
+            info->fprintf_func(info->stream, "%02x", buf[i]);
         }
-        info->fprintf_func(info->stream, "%02x", buf[i]);
+    } else {
+        info->fprintf_func(info->stream, "unable to read memory");
     }
-
-    g_free(buf);
     return n;
 }
 

disas/capstone.c

@@ -191,37 +191,43 @@ bool cap_disas_target(disassemble_info *info, uint64_t pc, size_t size)
         size_t tsize = MIN(sizeof(cap_buf) - csize, size);
         const uint8_t *cbuf = cap_buf;
 
-        info->read_memory_func(pc + csize, cap_buf + csize, tsize, info);
-        csize += tsize;
-        size -= tsize;
+        if (info->read_memory_func(pc + csize, cap_buf + csize, tsize, info) == 0) {
+            csize += tsize;
+            size -= tsize;
 
-        while (cs_disasm_iter(handle, &cbuf, &csize, &pc, insn)) {
-            cap_dump_insn(info, insn);
-        }
+            while (cs_disasm_iter(handle, &cbuf, &csize, &pc, insn)) {
+                cap_dump_insn(info, insn);
+            }
+
+            /* If the target memory is not consumed, go back for more... */
+            if (size != 0) {
+                /*
+                 * ... taking care to move any remaining fractional insn
+                 * to the beginning of the buffer.
+                 */
+                if (csize != 0) {
+                    memmove(cap_buf, cbuf, csize);
+                }
+                continue;
+            }
 
-        /* If the target memory is not consumed, go back for more... */
-        if (size != 0) {
             /*
-             * ... taking care to move any remaining fractional insn
-             * to the beginning of the buffer.
+             * Since the target memory is consumed, we should not have
+             * a remaining fractional insn.
              */
             if (csize != 0) {
-                memmove(cap_buf, cbuf, csize);
+                info->fprintf_func(info->stream,
+                                   "Disassembler disagrees with translator "
+                                   "over instruction decoding\n"
+                                   "Please report this to qemu-devel@nongnu.org\n");
             }
-            continue;
-        }
+            break;
 
-        /*
-         * Since the target memory is consumed, we should not have
-         * a remaining fractional insn.
-         */
-        if (csize != 0) {
+        } else {
             info->fprintf_func(info->stream,
-                "Disassembler disagrees with translator "
-                "over instruction decoding\n"
-                "Please report this to qemu-devel@nongnu.org\n");
+                               "0x%08" PRIx64 ": unable to read memory\n", pc);
+            break;
         }
-        break;
     }
 
     cs_close(&handle);
@@ -286,16 +292,23 @@ bool cap_disas_monitor(disassemble_info *info, uint64_t pc, int count)
 
         /* Make certain that we can make progress.  */
         assert(tsize != 0);
-        info->read_memory_func(pc + csize, cap_buf + csize, tsize, info);
-        csize += tsize;
-
-        if (cs_disasm_iter(handle, &cbuf, &csize, &pc, insn)) {
-            cap_dump_insn(info, insn);
-            if (--count <= 0) {
-                break;
+        if (info->read_memory_func(pc + csize, cap_buf + csize,
+                                   tsize, info) == 0)
+        {
+            csize += tsize;
+
+            if (cs_disasm_iter(handle, &cbuf, &csize, &pc, insn)) {
+                cap_dump_insn(info, insn);
+                if (--count <= 0) {
+                    break;
+                }
             }
+            memmove(cap_buf, cbuf, csize);
+        } else {
+            info->fprintf_func(info->stream,
+                               "0x%08" PRIx64 ": unable to read memory\n", pc);
+            break;
         }
-        memmove(cap_buf, cbuf, csize);
     }
 
     cs_close(&handle);