tests: fix build on musl-based systems

Musl libc does not provide the backtrace functions in its implementation.
These functions are typically provided by glibc's <execinfo.h>.

As a fallback for musl-based systems, support linking against the external
libunwind library and using dladdr() to obtain similar stack trace info.

Note that the usage of dladdr() is similar to that of backtrace_symbols in
glibc, and it can be used with glibc as well.

Signed-off-by: Alexey Kodanev <aleksei.kodanev@bell-sw.com>

Author: akodanev

include/test.mk

@@ -13,6 +13,17 @@ DEBUG_PRINTS ?= 0
 OPTIMIZATIONS=-O2 -ggdb
 CFLAGS_LTO =
 CFLAGS_GCOV =
+LIBS = -lefivar
+BACKTRACE_DEFINES ?=
+
+INCL_LIBUNWIND = '\#include <libunwind.h>'
+HAVE_LIBUNWIND := $(shell echo $(INCL_LIBUNWIND) | $(CC) -E - >/dev/null 2>&1 && echo 1 || echo 0)
+
+ifeq ($(HAVE_LIBUNWIND),1)
+BACKTRACE_DEFINES = -DHAVE_LIBUNWIND
+LIBS += -lunwind
+endif
+
 CFLAGS = $(OPTIMIZATIONS) -std=gnu11 \
 	 -isystem $(TOPDIR)/include/system \
 	 $(EFI_INCLUDES) \
@@ -44,7 +55,8 @@ CFLAGS = $(OPTIMIZATIONS) -std=gnu11 \
 	 -DEFI_FUNCTION_WRAPPER \
 	 -DGNU_EFI_USE_MS_ABI -DPAGE_SIZE=4096 \
 	 -DSHIM_UNIT_TEST \
-	 "-DDEFAULT_DEBUG_PRINT_STATE=$(DEBUG_PRINTS)"
+	 "-DDEFAULT_DEBUG_PRINT_STATE=$(DEBUG_PRINTS)" \
+	 $(BACKTRACE_DEFINES)
 
 # On some systems (e.g. Arch Linux), limits.h is in the "include-fixed" instead
 # of the "include" directory
@@ -109,7 +121,7 @@ tests := $(patsubst %.c,%,$(wildcard test-*.c))
 $(tests) :: test-% : | libefi-test.a
 
 $(tests) :: test-% : test.c test-%.c $(test-%_FILES)
-	$(CC) $(CFLAGS) -o $@ $(sort $^ $(wildcard $*.c) $(test-$*_FILES)) libefi-test.a -lefivar
+	$(CC) $(CFLAGS) -o $@ $(sort $^ $(wildcard $*.c) $(test-$*_FILES)) libefi-test.a $(LIBS)
 	$(VALGRIND) ./$@
 
 test : $(tests)

test-load-options.c

@@ -14,7 +14,6 @@
 
 #include "shim.h"
 
-#include <execinfo.h>
 #include <stdio.h>
 #include <efivar/efivar.h>
 

test.c

@@ -6,10 +6,20 @@
 
 #include "shim.h"
 
-#include <execinfo.h>
 #include <stdio.h>
 #include <string.h>
 
+#if defined(__GLIBC__)
+#include <execinfo.h>
+#elif defined(HAVE_LIBUNWIND)
+#include <stddef.h>
+#include <dlfcn.h>
+/* no backtrace() prototype in libunwind.h, however the library adds the symbol */
+extern int backtrace(void **buffer, int size);
+#else
+static int backtrace(void **buffer, int size) { (void)buffer; (void)size; return 0; }
+#endif
+
 #define BT_BUF_SIZE (4096/sizeof(void *))
 
 static void *frames[BT_BUF_SIZE] = { 0, };
@@ -20,19 +30,33 @@ int debug = DEFAULT_DEBUG_PRINT_STATE;
 void
 print_traceback(int skip)
 {
-	int nptrs;
-	char **strings;
-
-	nptrs = backtrace(frames, BT_BUF_SIZE);
-	if (nptrs < skip)
+	int nptrs = backtrace(frames, BT_BUF_SIZE);
+	if (nptrs <= skip)
 		return;
 
-	strings = backtrace_symbols(frames, nptrs);
-	for (int i = skip; strings != NULL && i < nptrs; i++) {
+#if defined(__GLIBC__)
+	char **strings = backtrace_symbols(frames, nptrs);
+	for (int i = skip; strings != NULL && i < nptrs; i++)
 		printf("%p %s\n", (void *)frames[i], strings[i]);
+	free(strings);
+#elif defined(HAVE_LIBUNWIND)
+	for (int i = skip; i < nptrs; ++i) {
+		void *addr = frames[i];
+		Dl_info dlinfo;
+
+		if (!dladdr(addr, &dlinfo)) {
+			printf("%p\n", addr);
+			continue;
+		}
+
+		ptrdiff_t offset = addr - dlinfo.dli_saddr;
+		printf("%p %s(%s%c%#tx)\n", addr,
+			dlinfo.dli_fname ?: "",
+			dlinfo.dli_sname ?: "",
+			offset < 0 ? '-' : '+',
+			offset < 0 ? -offset : offset);
 	}
-	if (strings)
-		free(strings);
+#endif
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"