Fix freeze with empty NatFeats NF_STDERR("") string

Fixes: b2a81850 (introduced in 2.3.0)

Thanks to Matthias Arndt for reporting the issue, and Christian Zietz
for debugging the cause for it!

4 files changed, 11 insertions, 8 deletions

diff --git a/doc/release-notes.txt b/doc/release-notes.txt
index d8db37f..7133303 100644
--- a/doc/release-notes.txt
+++ b/doc/release-notes.txt
@@ -103,6 +103,8 @@ Emulator improvements:
 - Command line:
   - Support "off" as alias for "none" when disabling DSP, FPU,
     Joysticks and VME, for consistency with HW on/off options
+- NatFeats:
+  - Fix: freeze with NF_STDERR("")
 - Debugger:
   - Fix: profile header so that profile data post-processor knows how
     to parse built-in WinAUE CPU core ("uae") disassembly output, not
diff --git a/src/debug/natfeats.c b/src/debug/natfeats.c
index 517ed1e..8d4e163 100644
--- a/src/debug/natfeats.c
+++ b/src/debug/natfeats.c
@@ -1,7 +1,7 @@
 /*
  * Hatari - natfeats.c
  * 
- * Copyright (C) 2012-2016, 2019 by Eero Tamminen
+ * Copyright (C) 2012-2016, 2019-2022 by Eero Tamminen
  *
  * This file is distributed under the GNU General Public License, version 2
  * or at your option any later version. Read the file gpl.txt for details.
@@ -46,7 +46,7 @@ const char Natfeats_fileid[] = "Hatari natfeats.c";
  * Check whether given string address is valid
  * and whether strings is of "reasonable" length.
  *
- * Returns string length or zero for error.
+ * Returns string length or negative value for error.
  */
 static int mem_string_ok(Uint32 addr)
 {
@@ -56,7 +56,7 @@ static int mem_string_ok(Uint32 addr)
 	if (!STMemory_CheckAreaType(addr, 1, ABFLAG_RAM | ABFLAG_ROM)) {
 		/* invalid starting address -> error */
 		M68000_BusError(addr, BUS_ERROR_READ, BUS_ERROR_SIZE_BYTE, BUS_ERROR_ACCESS_DATA, 0);
-		return 0;
+		return -1;
 	}
 	buf = (const char *)STMemory_STAddrToPointer(addr);
 	if (STMemory_CheckAreaType(addr, NF_MAX_STRING, ABFLAG_RAM | ABFLAG_ROM)) {
@@ -66,19 +66,19 @@ static int mem_string_ok(Uint32 addr)
 				return i;
 			}
 		}
-		return 0;
+		return -1;
 	}
 	for (i = 0; i < NF_MAX_STRING; i++) {
 		if (!STMemory_CheckAreaType(addr, 1, ABFLAG_RAM | ABFLAG_ROM)) {
 			/* ends in invalid area -> error */
 			M68000_BusError(addr, BUS_ERROR_READ, BUS_ERROR_SIZE_BYTE, BUS_ERROR_ACCESS_DATA, 0);
-			return 0;
+			return -1;
 		}
 		if (!buf[i]) {
 			return i;
 		}
 	}
-	return 0;
+	return -1;
 }
 
 /**
@@ -143,7 +143,7 @@ static bool nf_stderr(Uint32 stack, Uint32 subid, Uint32 *retval)
 		/* unrecognized subid, nothing printed */
 		return true;
 	}
-	if (!mem_string_ok(ptr)) {
+	if (mem_string_ok(ptr) < 0) {
 		return false;
 	}
 	str = (const char *)STMemory_STAddrToPointer (ptr);
@@ -258,7 +258,7 @@ static bool nf_command(Uint32 stack, Uint32 subid, Uint32 *retval)
 		return true;
 	}
 	ptr = STMemory_ReadLong(stack);
-	if (!mem_string_ok(ptr)) {
+	if (mem_string_ok(ptr) < 0) {
 		return false;
 	}
 	buffer = (const char *)STMemory_STAddrToPointer(ptr);
diff --git a/tests/natfeats/natfeats.c b/tests/natfeats/natfeats.c
index 0b455b8..7ea2f49 100644
--- a/tests/natfeats/natfeats.c
+++ b/tests/natfeats/natfeats.c
@@ -200,6 +200,7 @@ int main()
 	old_ff = nf_fastforward(1);
 	nf_print("Emulator name:\n");
 	nf_showname();
+	nf_print(""); /* check regression b2a81850 + its fix */
 	nf_print("Invoking debugger...\n");
 	nf_debugger();
 	nf_print("Restoring fastforward & shutting down...\n");
diff --git a/tests/natfeats/nf_ahcc.tos b/tests/natfeats/nf_ahcc.tos
index dfbc971..ff93ab0 100644
--- a/tests/natfeats/nf_ahcc.tos
+++ b/tests/natfeats/nf_ahcc.tos