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-rw-r--r--src/common/linux/dwarf_line_to_module.cc8
-rw-r--r--src/common/linux/dwarf_line_to_module.h62
-rw-r--r--src/common/linux/dwarf_line_to_module_unittest.cc72
3 files changed, 142 insertions, 0 deletions
diff --git a/src/common/linux/dwarf_line_to_module.cc b/src/common/linux/dwarf_line_to_module.cc
index bc1cd507..c740fa30 100644
--- a/src/common/linux/dwarf_line_to_module.cc
+++ b/src/common/linux/dwarf_line_to_module.cc
@@ -102,6 +102,14 @@ void DwarfLineToModule::AddLine(uint64 address, uint64 length,
if (address + length < address)
length = -address;
+ // Should we omit this line? (See the comments for omitted_line_end_.)
+ if (address == 0 || address == omitted_line_end_) {
+ omitted_line_end_ = address + length;
+ return;
+ } else {
+ omitted_line_end_ = 0;
+ }
+
// Find the source file being referred to.
Module::File *file = files_[file_num];
if (!file) {
diff --git a/src/common/linux/dwarf_line_to_module.h b/src/common/linux/dwarf_line_to_module.h
index ab8bf11d..7ff466d7 100644
--- a/src/common/linux/dwarf_line_to_module.h
+++ b/src/common/linux/dwarf_line_to_module.h
@@ -52,6 +52,62 @@ namespace google_breakpad {
// uses it to produce a vector of google_breakpad::Module::Line
// objects, referring to google_breakpad::Module::File objects added
// to a particular google_breakpad::Module.
+//
+// GNU toolchain omitted sections support:
+// ======================================
+//
+// Given the right options, the GNU toolchain will omit unreferenced
+// functions from the final executable. Unfortunately, when it does so, it
+// does not remove the associated portions of the DWARF line number
+// program; instead, it gives the DW_LNE_set_address instructions referring
+// to the now-deleted code addresses of zero. Given this input, the DWARF
+// line parser will call AddLine with a series of lines starting at address
+// zero. For example, here is the output from 'readelf -wl' for a program
+// with four functions, the first three of which have been omitted:
+//
+// Line Number Statements:
+// Extended opcode 2: set Address to 0x0
+// Advance Line by 14 to 15
+// Copy
+// Special opcode 48: advance Address by 3 to 0x3 and Line by 1 to 16
+// Special opcode 119: advance Address by 8 to 0xb and Line by 2 to 18
+// Advance PC by 2 to 0xd
+// Extended opcode 1: End of Sequence
+//
+// Extended opcode 2: set Address to 0x0
+// Advance Line by 14 to 15
+// Copy
+// Special opcode 48: advance Address by 3 to 0x3 and Line by 1 to 16
+// Special opcode 119: advance Address by 8 to 0xb and Line by 2 to 18
+// Advance PC by 2 to 0xd
+// Extended opcode 1: End of Sequence
+//
+// Extended opcode 2: set Address to 0x0
+// Advance Line by 19 to 20
+// Copy
+// Special opcode 48: advance Address by 3 to 0x3 and Line by 1 to 21
+// Special opcode 76: advance Address by 5 to 0x8 and Line by 1 to 22
+// Advance PC by 2 to 0xa
+// Extended opcode 1: End of Sequence
+//
+// Extended opcode 2: set Address to 0x80483a4
+// Advance Line by 23 to 24
+// Copy
+// Special opcode 202: advance Address by 14 to 0x80483b2 and Line by 1 to 25
+// Special opcode 76: advance Address by 5 to 0x80483b7 and Line by 1 to 26
+// Advance PC by 6 to 0x80483bd
+// Extended opcode 1: End of Sequence
+//
+// Instead of collecting runs of lines describing code that is not there,
+// we try to recognize and drop them. Since the linker doesn't explicitly
+// distinguish references to dropped sections from genuine references to
+// code at address zero, we must use a heuristic. We have chosen:
+//
+// - If a line starts at address zero, omit it. (On the platforms
+// breakpad targets, it is extremely unlikely that there will be code
+// at address zero.)
+//
+// - If a line starts immediately after an omitted line, omit it too.
class DwarfLineToModule: public dwarf2reader::LineInfoHandler {
public:
// As the DWARF line info parser passes us line records, add source
@@ -65,6 +121,7 @@ class DwarfLineToModule: public dwarf2reader::LineInfoHandler {
: module_(module),
lines_(lines),
highest_file_number_(-1),
+ omitted_line_end_(0),
warned_bad_file_number_(false),
warned_bad_directory_number_(false) { }
@@ -106,6 +163,11 @@ class DwarfLineToModule: public dwarf2reader::LineInfoHandler {
// The highest file number we've seen so far, or -1 if we've seen
// none. Used for dynamically defined file numbers.
int32 highest_file_number_;
+
+ // This is the ending address of the last line we omitted, or zero if we
+ // didn't omit the previous line. It is zero before we have received any
+ // AddLine calls.
+ uint64 omitted_line_end_;
// True if we've warned about:
bool warned_bad_file_number_; // bad file numbers
diff --git a/src/common/linux/dwarf_line_to_module_unittest.cc b/src/common/linux/dwarf_line_to_module_unittest.cc
index 4b9743ce..54411591 100644
--- a/src/common/linux/dwarf_line_to_module_unittest.cc
+++ b/src/common/linux/dwarf_line_to_module_unittest.cc
@@ -265,3 +265,75 @@ TEST(Errors, BigLine) {
ASSERT_EQ(1U, lines.size());
EXPECT_EQ(1U, lines[0].size);
}
+
+// The 'Omitted' tests verify that we correctly omit line information
+// for code in sections that the linker has dropped. See "GNU
+// toolchain omitted sections support" at the top of the
+// DwarfLineToModule class.
+
+TEST(Omitted, DroppedThenGood) {
+ Module m("name", "os", "architecture", "id");
+ vector<Module::Line> lines;
+ DwarfLineToModule h(&m, &lines);
+
+ h.DefineFile("filename1", 1, 0, 0, 0);
+ h.AddLine(0, 10, 1, 83816211, 0); // should be omitted
+ h.AddLine(20, 10, 1, 13059195, 0); // should be recorded
+
+ ASSERT_EQ(1U, lines.size());
+ EXPECT_EQ(13059195, lines[0].number);
+}
+
+TEST(Omitted, GoodThenDropped) {
+ Module m("name", "os", "architecture", "id");
+ vector<Module::Line> lines;
+ DwarfLineToModule h(&m, &lines);
+
+ h.DefineFile("filename1", 1, 0, 0, 0);
+ h.AddLine(0x9dd6a372, 10, 1, 41454594, 0); // should be recorded
+ h.AddLine(0, 10, 1, 44793413, 0); // should be omitted
+
+ ASSERT_EQ(1U, lines.size());
+ EXPECT_EQ(41454594, lines[0].number);
+}
+
+TEST(Omitted, Mix1) {
+ Module m("name", "os", "architecture", "id");
+ vector<Module::Line> lines;
+ DwarfLineToModule h(&m, &lines);
+
+ h.DefineFile("filename1", 1, 0, 0, 0);
+ h.AddLine(0x679ed72f, 10, 1, 58932642, 0); // should be recorded
+ h.AddLine(0xdfb5a72d, 10, 1, 39847385, 0); // should be recorded
+ h.AddLine(0, 0x78, 1, 23053829, 0); // should be omitted
+ h.AddLine(0x78, 0x6a, 1, 65317783, 0); // should be omitted
+ h.AddLine(0x78 + 0x6a, 0x2a, 1, 77601423, 0); // should be omitted
+ h.AddLine(0x9fe0cea5, 10, 1, 91806582, 0); // should be recorded
+ h.AddLine(0x7e41a109, 10, 1, 56169221, 0); // should be recorded
+
+ ASSERT_EQ(4U, lines.size());
+ EXPECT_EQ(58932642, lines[0].number);
+ EXPECT_EQ(39847385, lines[1].number);
+ EXPECT_EQ(91806582, lines[2].number);
+ EXPECT_EQ(56169221, lines[3].number);
+}
+
+TEST(Omitted, Mix2) {
+ Module m("name", "os", "architecture", "id");
+ vector<Module::Line> lines;
+ DwarfLineToModule h(&m, &lines);
+
+ h.DefineFile("filename1", 1, 0, 0, 0);
+ h.AddLine(0, 0xf2, 1, 58802211, 0); // should be omitted
+ h.AddLine(0xf2, 0xb9, 1, 78958222, 0); // should be omitted
+ h.AddLine(0xf2 + 0xb9, 0xf7, 1, 64861892, 0); // should be omitted
+ h.AddLine(0x4e4d271e, 9, 1, 67355743, 0); // should be recorded
+ h.AddLine(0xdfb5a72d, 30, 1, 23365776, 0); // should be recorded
+ h.AddLine(0, 0x64, 1, 76196762, 0); // should be omitted
+ h.AddLine(0x64, 0x33, 1, 71066611, 0); // should be omitted
+ h.AddLine(0x64 + 0x33, 0xe3, 1, 61749337, 0); // should be omitted
+
+ ASSERT_EQ(2U, lines.size());
+ EXPECT_EQ(67355743, lines[0].number);
+ EXPECT_EQ(23365776, lines[1].number);
+}
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