Fix a potential crash with tracing (sim_core.c) and add a check

for a null-pointer return from elf_strptr().
That should be a fix for Bug #303 - "segfault when running simduino.elf".

Author: ga

simavr/sim/sim_core.c

@@ -126,7 +126,7 @@ static const char *get_data_address_string(avr_t* avr, uint16_t addr)
 }
 
 #define DAS(addr) get_data_address_string(avr, addr)
-#define FAS(addr) (((addr >> 1) > avr->trace_data->codeline_size) ? \
+#define FAS(addr) (((addr >> 1) >= avr->trace_data->codeline_size) ? \
                    "[not loaded]" : avr->trace_data->codeline[addr >> 1])
 
 void crash(avr_t* avr)

simavr/sim/sim_elf.c

@@ -553,7 +553,7 @@ elf_read_firmware(
 		char * name = elf_strptr(elf, elf_header.e_shstrndx, shdr.sh_name);
 		//	printf("Walking elf section '%s'\n", name);
 
-		if (!strcmp(name, ".mmcu")) {
+		if (name && !strcmp(name, ".mmcu")) {
 			Elf_Data *s = elf_getdata(scn, NULL);
 
 			elf_parse_mmcu_section(firmware, s->d_buf, s->d_size);