lib/core: Use libdw to decode stack trace with debugging symbols, v2.

libdw is a new dependency built from the elfutils package. It provides
us a way to generate line numbers and file names from the instruction
pointer.

elfutils is LGPLv3 or GPLv2, so it's ok to link against it.

Before:
IGT-Version: 1.23-g8ae86abd419d (x86_64) (Linux: 4.16.0-1-amd64 x86_64)
Starting subtest: fail-result
(meta_test:29661) CRITICAL: Test assertion failure function test_result, file ../tests/meta_test.c:94:
(meta_test:29661) CRITICAL: Failed assertion: result == 1
(meta_test:29661) CRITICAL: error: 0 != 1
Stack trace:
  #0 [__igt_fail_assert+0x20a]
  #1 [test_result+0x7a]
  #2 [__real_main120+0x240]
  #3 [main+0x4a]
  #4 (../csu/libc-start.c) __libc_start_main:344
  #5 [_start+0x2a]

After:
IGT-Version: 1.23-g8ae86abd419d (x86_64) (Linux: 4.16.0-1-amd64 x86_64)
Starting subtest: fail-result
(meta_test:1357) CRITICAL: Test assertion failure function test_result, file ../tests/meta_test.c:94:
(meta_test:1357) CRITICAL: Failed assertion: result == 1
(meta_test:1357) CRITICAL: error: 0 != 1
Stack trace:
  #0 ../lib/igt_core.c:1467 __igt_fail_assert()
  #1 ../tests/meta_test.c:95 test_result()
  #2 ../tests/meta_test.c:137 __real_main120()
  #3 ../tests/meta_test.c:120 main()
  #4 ../csu/libc-start.c:344 __libc_start_main()
  #5 [_start+0x2a]

Changes since v1:
- Add libdw dependency to readme.
- Change backtrace format slightly.

Cc: Petri Latvala <petri.latvala@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
[mlankhorst: Add description about libdw in commit msg, name -> dwfl_name]
Reviewed-by: Petri Latvala <petri.latvala@intel.com>

1 files changed, 45 insertions, 5 deletions

diff --git a/lib/igt_core.c b/lib/igt_core.c
index c52c0818..23bb858f 100644
--- a/lib/igt_core.c
+++ b/lib/igt_core.c
@@ -73,6 +73,7 @@
 
 #define UNW_LOCAL_ONLY
 #include <libunwind.h>
+#include <elfutils/libdwfl.h>
 
 #ifdef HAVE_LIBGEN_H
 #include <libgen.h>   /* for basename() on Solaris */
@@ -1212,20 +1213,59 @@ static void print_backtrace(void)
 	unw_context_t uc;
 	int stack_num = 0;
 
+	Dwfl_Callbacks cbs = {
+		.find_elf = dwfl_linux_proc_find_elf,
+		.find_debuginfo = dwfl_standard_find_debuginfo,
+	};
+
+	Dwfl *dwfl = dwfl_begin(&cbs);
+
+	if (dwfl_linux_proc_report(dwfl, getpid())) {
+		dwfl_end(dwfl);
+		dwfl = NULL;
+	} else
+		dwfl_report_end(dwfl, NULL, NULL);
+
 	igt_info("Stack trace:\n");
 
 	unw_getcontext(&uc);
 	unw_init_local(&cursor, &uc);
 	while (unw_step(&cursor) > 0) {
 		char name[255];
-		unw_word_t off;
+		unw_word_t off, ip;
+		Dwfl_Module *mod = NULL;
 
-		if (unw_get_proc_name(&cursor, name, 255, &off) < 0)
-			strcpy(name, "<unknown>");
+		unw_get_reg(&cursor, UNW_REG_IP, &ip);
+
+		if (dwfl)
+			mod = dwfl_addrmodule(dwfl, ip);
 
-		igt_info("  #%d [%s+0x%x]\n", stack_num++, name,
-			 (unsigned int) off);
+		if (mod) {
+			const char *src, *dwfl_name;
+			Dwfl_Line *line;
+			int lineno;
+			GElf_Sym sym;
+
+			line = dwfl_module_getsrc(mod, ip);
+			dwfl_name = dwfl_module_addrsym(mod, ip, &sym, NULL);
+
+			if (line && dwfl_name) {
+				src = dwfl_lineinfo(line, NULL, &lineno, NULL, NULL, NULL);
+				igt_info("  #%d %s:%d %s()\n", stack_num++, src, lineno, dwfl_name);
+				continue;
+			}
+		}
+
+		if (unw_get_proc_name(&cursor, name, 255, &off) < 0)
+			igt_info("  #%d [<unknown>+0x%x]\n", stack_num++,
+				 (unsigned int) ip);
+		else
+			igt_info("  #%d [%s+0x%x]\n", stack_num++, name,
+				 (unsigned int) off);
 	}
+
+	if (dwfl)
+		dwfl_end(dwfl);
 }
 
 static const char hex[] = "0123456789abcdef";