[PATCH 1/4] perf libdw: Find the CU by iterating all CUs when aranges are missing

[James Clark <james.clark@linaro.org>]

libdw__addr2line() finds the CU with dwfl_module_getsrc() and
dwfl_module_addrdie(), which use dwarf_getaranges(). In elfutils 0.190
this only reads .debug_aranges, which can be partial. For example, when
Perf is built with LLVM=1, clang doesn't emit .debug_aranges by default
so the lookup then fails and no source lines are found for most of the
Perf binary.

This used to be hidden by falling back to the next addr2line style, but
now missing information stops the fallback since commit (62d7cdc8d587
"perf libdw: Optimize fallback logic for missing DWARF").

find_cu_die() in annotate-data.c already handles partial aranges by
iterating all CUs in .debug_info and checking them with dwarf_haspc().
Move it to dwarf-aux.c, then look up the line in that CU with
dwarf_getsrc_die() and use the same CU for unwinding inlines. While
moving it, don't treat a dwarf_haspc() error as a match.

This fixes the "test addr2line inline unwinding" test when Perf is built
with LLVM:

  $ perf test -vvv "test addr2line inline unwinding"
  ...
  Inline unwinding fp verification test [Failed missing inlined functions]
  ...
  Inline unwinding dwarf verification test [Failed missing inlined functions]
  ...
  Inline unwinding lbr verification test [Failed missing inlined functions]
  ---- end(-1) ----
   79: test addr2line inline unwinding : FAILED!

Fixes: 88c51002d06f ("perf addr2line: Add a libdw implementation")
Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/perf/util/annotate-data.c | 27 +--------------------------
 tools/perf/util/dwarf-aux.c     | 37 +++++++++++++++++++++++++++++++++++++
 tools/perf/util/dwarf-aux.h     |  3 +++
 tools/perf/util/libdw.c         | 19 ++++++++++---------
 4 files changed, 51 insertions(+), 35 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 25e3169ea8ad..8092ef9d2045 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -523,31 +523,6 @@ static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
 	return result;
 }
 
-static bool find_cu_die(struct debuginfo *di, u64 pc, Dwarf_Die *cu_die)
-{
-	Dwarf_Off off, next_off;
-	size_t header_size;
-
-	if (dwarf_addrdie(di->dbg, pc, cu_die) != NULL)
-		return cu_die;
-
-	/*
-	 * There are some kernels don't have full aranges and contain only a few
-	 * aranges entries.  Fallback to iterate all CU entries in .debug_info
-	 * in case it's missing.
-	 */
-	off = 0;
-	while (dwarf_nextcu(di->dbg, off, &next_off, &header_size,
-			    NULL, NULL, NULL) == 0) {
-		if (dwarf_offdie(di->dbg, off + header_size, cu_die) &&
-		    dwarf_haspc(cu_die, pc))
-			return true;
-
-		off = next_off;
-	}
-	return false;
-}
-
 enum type_match_result {
 	PERF_TMR_UNKNOWN = 0,
 	PERF_TMR_OK,
@@ -1827,7 +1802,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
 	pc = map__rip_2objdump(dloc->ms->map, dloc->ip);
 
 	/* Get a compile_unit for this address */
-	if (!find_cu_die(dloc->di, pc, &cu_die)) {
+	if (!cu_find_by_addr(dloc->di->dbg, pc, &cu_die)) {
 		pr_debug_dtp("cannot find CU for address %"PRIx64"\n", pc);
 		ann_data_stat.no_cuinfo++;
 		return -1;
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 54f8b5ec74a2..742fccba5376 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -106,6 +106,43 @@ static Dwarf_Line *cu_getsrc_die(Dwarf_Die *cu_die, Dwarf_Addr addr)
 	return line;
 }
 
+/**
+ * cu_find_by_addr - Find the CU DIE that contains an address
+ * @dbg: a Dwarf handle
+ * @addr: An address
+ * @cu_die: a buffer to store the found CU DIE
+ *
+ * Find the CU DIE whose ranges contain @addr. dwarf_addrdie() uses
+ * dwarf_getaranges() which didn't work until elfutils 0.191. Release notes:
+ *
+ *   * NEWS *
+ *   libdw: dwarf_addrdie now supports binaries lacking a .debug_aranges
+ *   section.
+ *
+ * Clang doesn't emit them by default, so fall back to iterating all CUs in
+ * case it's missing.
+ *
+ * Return @cu_die if found, otherwise NULL.
+ */
+Dwarf_Die *cu_find_by_addr(Dwarf *dbg, Dwarf_Addr addr, Dwarf_Die *cu_die)
+{
+	Dwarf_Off off = 0, next_off;
+	size_t header_size;
+
+	if (dwarf_addrdie(dbg, addr, cu_die) && dwarf_haspc(cu_die, addr) == 1)
+		return cu_die;
+
+	while (dwarf_nextcu(dbg, off, &next_off, &header_size,
+			    NULL, NULL, NULL) == 0) {
+		if (dwarf_offdie(dbg, off + header_size, cu_die) &&
+		    dwarf_haspc(cu_die, addr) == 1)
+			return cu_die;
+
+		off = next_off;
+	}
+	return NULL;
+}
+
 /**
  * cu_find_lineinfo - Get a line number and file name for given address
  * @cu_die: a CU DIE
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 6f9145510adc..cc3fd61374c4 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -23,6 +23,9 @@ const char *cu_find_realpath(Dwarf_Die *cu_die, const char *fname);
 /* Get DW_AT_comp_dir (should be NULL with older gcc) */
 const char *cu_get_comp_dir(Dwarf_Die *cu_die);
 
+/* Find the CU DIE that contains the given address */
+Dwarf_Die *cu_find_by_addr(Dwarf *dbg, Dwarf_Addr addr, Dwarf_Die *cu_die);
+
 /* Get a line number and file name for given address */
 int cu_find_lineinfo(Dwarf_Die *cudie, Dwarf_Addr addr,
 		     const char **fname, int *lineno);
diff --git a/tools/perf/util/libdw.c b/tools/perf/util/libdw.c
index e660623338d5..90767361f485 100644
--- a/tools/perf/util/libdw.c
+++ b/tools/perf/util/libdw.c
@@ -170,7 +170,9 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
 {
 	Dwfl *dwfl;
 	Dwfl_Module *mod;
-	Dwfl_Line *dwline;
+	Dwarf_Line *dwline;
+	Dwarf_Die cu_mem, *cudie;
+	Dwarf *dw;
 	Dwarf_Addr bias;
 	const char *src;
 	int lineno = 0;
@@ -197,7 +199,8 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
 	 * between the regular ELF addr2line addresses and those to use with
 	 * libdw.
 	 */
-	if (!dwfl_module_getdwarf(mod, &bias)) {
+	dw = dwfl_module_getdwarf(mod, &bias);
+	if (!dw) {
 		/*
 		 * Free the Dwfl session so the mmap'd ELF binary is unmapped
 		 * immediately, and mark the DSO as lacking srcline/DWARF info
@@ -211,7 +214,8 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
 	}
 
 	/* Find source line information for the address. */
-	dwline = dwfl_module_getsrc(mod, addr + bias);
+	cudie = cu_find_by_addr(dw, addr, &cu_mem);
+	dwline = cudie ? dwarf_getsrc_die(cudie, addr) : NULL;
 	if (!dwline) {
 		/* conclusively missing information -> abort fallbacks */
 		ret = 0;
@@ -219,8 +223,8 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
 	}
 
 	/* Get line information. */
-	src = dwfl_lineinfo(dwline, /*addr=*/NULL, &lineno, /*col=*/NULL, /*mtime=*/NULL,
-			    /*length=*/NULL);
+	src = dwarf_linesrc(dwline, /*mtime=*/NULL, /*length=*/NULL);
+	dwarf_lineno(dwline, &lineno);
 
 	if (file)
 		*file = src ? strdup(src) : NULL;
@@ -229,8 +233,6 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
 
 	/* Optionally unwind inline function call chain. */
 	if (unwind_inlines && node) {
-		Dwarf_Addr unused_bias;
-		Dwarf_Die *cudie = dwfl_module_addrdie(mod, addr + bias, &unused_bias);
 		struct libdw_a2l_cb_args args = {
 			.dso = dso,
 			.sym = sym,
@@ -248,8 +250,7 @@ int libdw__addr2line(u64 addr, char **file, unsigned int *line_nr,
 		}
 
 		/* Walk from the parent down to the leaf. */
-		if (cudie)
-			cu_walk_functions_at(cudie, addr, libdw_a2l_cb, &args);
+		cu_walk_functions_at(cudie, addr, libdw_a2l_cb, &args);
 
 		if (!args.leaf_srcline_used)
 			free(args.leaf_srcline);

-- 
2.43.0