Check for installations of libelf and libdwarf when building and

adjust build to suit.

Makefile

@@ -14,7 +14,7 @@ PREFIX = ${DESTDIR}
 
 all:	build-simavr build-tests build-examples build-parts
 
-build-simavr:
+build-simavr: Libs.mk
 	$(MAKE) -C simavr RELEASE=$(RELEASE)
 
 build-tests: build-simavr
@@ -34,6 +34,28 @@ install-simavr:
 install-parts:
 	$(MAKE) -C examples/parts install RELEASE=$(RELEASE) DESTDIR=$(DESTDIR) PREFIX=$(PREFIX)
 
+
+# Find whether libelf and libdwarf are available.
+
+Libs.mk:
+	@echo CONF $@
+	@echo "# Autogenerated: do not edit." > $@
+	@if \
+	  echo  "#include <libelf.h>" > testit.c && \
+	  $(CC) -E $(CFLAGS) ${AVR_CPPFLAGS} testit.c  > /dev/null 2>&1 ; \
+	then  \
+	  echo CFLAGS += -DHAVE_LIBELF >> $@ ; \
+	  echo LDFLAGS += -lelf >> $@ ; \
+	  if \
+	    echo  "#include <dwarf.h>" > testit.c && \
+	    $(CC) -E $(CFLAGS) ${AVR_CPPFLAGS} testit.c > /dev/null 2>&1 ; \
+	  then  \
+	    echo CFLAGS += -DHAVE_LIBDWARF >> $@ ; \
+	    echo LDFLAGS += -ldwarf >> $@ ; \
+	  fi \
+	fi
+	@rm -f testit.c
+
 doc:
 	$(MAKE) -C doc RELEASE=$(RELEASE)
 
@@ -43,4 +65,5 @@ clean:
 	$(MAKE) -C examples clean
 	$(MAKE) -C examples/parts clean
 	$(MAKE) -C doc clean
+	rm -f Libs.mk
 

Makefile.common

@@ -114,7 +114,13 @@ OBJ 		:= obj-${shell $(CC) -dumpmachine}
 LIBDIR		:= ${shell pwd}/${SIMAVR}/${OBJ}
 LDFLAGS 	+= -L${LIBDIR} -lsimavr -lm
 
-LDFLAGS 	+= -lelf -ldwarf
+# Are libelf and/or libdwarf installed?
+# The included file is created when running "make" at the top level.
+
+ifeq ($(shell test -f $(SIMAVR)/../Libs.mk || echo Exists), Exists)
+$(warning Missing library configuration file.  Make from top level to create it.)
+endif
+-include $(SIMAVR)/../Libs.mk
 
 ifeq (${WIN}, Msys)
 LDFLAGS      += -lws2_32

simavr/sim/sim_dwarf.c

@@ -5,7 +5,7 @@
 	Extract debug symbols and line numbers from  .elf file for use
         by gdb ("info io_registers" command) and tracing.
 
-	Copyright 2021, Giles Atkinson
+	Copyright 2021, 2022 Giles Atkinson
 
  	This file is part of simavr.
 
@@ -23,6 +23,8 @@
 	along with simavr.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifdef HAVE_LIBDWARF
+
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -349,3 +351,8 @@ int avr_read_dwarf(avr_t *avr, const char *filename)
     close(fd);
     return 0;
 }
+
+# else // No libdwarf
+#include "sim_avr.h"
+int avr_read_dwarf(avr_t *avr, const char *filename) { return 0; }
+#endif

simavr/sim/sim_elf.c

@@ -29,8 +29,14 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+
+#ifdef HAVE_LIBELF
 #include <libelf.h>
 #include <gelf.h>
+#else
+#undef ELF_SYMBOLS
+#define ELF_SYMBOLS 0
+#endif
 
 #include "sim_elf.h"
 #include "sim_vcd_file.h"
@@ -91,12 +97,13 @@ avr_load_firmware(
 		avr->avcc = firmware->avcc;
 	if (firmware->aref)
 		avr->aref = firmware->aref;
-#if CONFIG_SIMAVR_TRACE && ELF_SYMBOLS
+#if ELF_SYMBOLS
+#if CONFIG_SIMAVR_TRACE
 	/* Store the symbols read from the ELF file. */
 
 	int           scount = firmware->flashsize >> 1;
 	uint32_t      addr;
-        const char ** table;
+	const char ** table;
 
 	// Allocate table of Flash address strings.
 
@@ -157,6 +164,7 @@ avr_load_firmware(
 		avr_read_dwarf(avr, firmware->dwarf_file);
 	free(firmware->dwarf_file);
 #endif
+#endif // ELF_SYMBOLS
 
 	avr_loadcode(avr, firmware->flash,
 			firmware->flashsize, firmware->flashbase);
@@ -270,6 +278,7 @@ avr_load_firmware(
 		avr_vcd_start(avr->vcd);
 }
 
+#ifdef HAVE_LIBELF
 static void
 elf_parse_mmcu_section(
 		elf_firmware_t * firmware,
@@ -623,3 +632,11 @@ elf_read_firmware(
 	close(fd);
 	return 0;
 }
+#else //  HAVE_LIBELF not defined.
+int
+elf_read_firmware(const char * file, elf_firmware_t * firmware)
+{
+	AVR_LOG(NULL, LOG_ERROR, "ELF format is not supported by this build.\n");
+	return -1;
+}
+#endif