Fix -u option in dsymutil, to not emit an extra DW_LNE_set_address if the original line table was empty

[rastogishubham]

Summary

With dsymutil's -u option, only the accelerator tables should be updated, but with https://reviews.llvm.org/D150554 the -u option will still re-generate the line table. If the line table was empty, that is, it was a dummy line table, with no entries in it, dsymutil will always generate a line table with a DW_LNE_end_sequence, a funky side effect of this is that when the line table is re-generated, it will always emit a DW_LNE_set_address first, which will change the line table total size. This patch addresses this by making sure that if all the line table has in it is a DW_LNE_end_sequence, it is the same as a dummy entry.

[rastogishubham]

Removed the

REQUIRES: darwin

line in the test

[JDevlieghere]

llvm/lib/DWARFLinker/DWARFStreamer.cpp

854–855 ↗

(On Diff #526170)

Would it make sense to hoist that into the LineTable class and have a method LineTable::empty() that returns exactly this?

[avl]

llvm/lib/DWARFLinker/DWARFStreamer.cpp

854–855 ↗

(On Diff #526170)

In that case LineTable::empty() would in fact not match with real number of LineTable.Rows(). It looks a bit sloppy.

Another alternative might be implementing what described in DWARFLinker.cpp:

// FIXME: this only removes the unneeded end_sequence if the
// sequences have been inserted in order. Using a global sort like
// described in generateLineTableForUnit() and delaying the end_sequene
// elimination to emitLineTableForUnit() we can get rid of all of them.

Running such cleanup code for no-update and update modes will probably make output equal for both modes.

[avl]

llvm/lib/DWARFLinker/DWARFStreamer.cpp

854–855 ↗

(On Diff #526170)

Or, if it is not a good moment to implementing such cleanup code then do simple version of it in DWARFLinker.cpp:

// Set Line Table Rows.
if (Linker.Options.Update) {
  LineTable.Rows = LT->Rows; 
  if (LineTable.Rows.size() == 1 && LineTable.Rows[0].EndSequence))
     LineTable.Rows.clear()

[rastogishubham]

clear the line table rows, if the update flag is set, and the line table just has a DW_LNE_end_sequence in DWARFLinker.cpp

[avl]

LGTM. Thank you!

llvm/lib/DWARFLinker/DWARFLinker.cpp

if (const DWARFDebugLine::LineTable *LT =
     DWARFDebugLine::LineTable LineTable;
 
     // Set Line Table header.
     LineTable.Prologue = LT->Prologue;
 
     // Set Line Table Rows.
     if (Linker.Options.Update) {
       LineTable.Rows = LT->Rows;
+      // If all the line table contains is a DW_LNE_end_sequence, clear the line
+      // table rows, it will be inserted again in the DWARFStreamer.
+      if (LineTable.Rows.size() == 1 && LineTable.Rows[0].EndSequence)
+        LineTable.Rows.clear();
 
       LineTable.Sequences = LT->Sequences;
     } else {
       RangesTy &Ranges = ObjFile.Addresses->getValidAddressRanges();
 
       // This vector is the output line table.
       std::vector<DWARFDebugLine::Row> NewRows;
       NewRows.reserve(LT->Rows.size());

llvm/test/tools/dsymutil/ARM/fat-dylib-update.test

+# REQUIRES: object-emission
+# RUN: dsymutil -oso-prepend-path %p/..  %p/../Inputs/fat-test.arm.dylib -o %t.dSYM
+# RUN: llvm-dwarfdump -a -v %t.dSYM/Contents/Resources/DWARF/fat-test.arm.dylib | FileCheck %s
+# RUN: dsymutil -u %t.dSYM
+# RUN: llvm-dwarfdump -a -v %t.dSYM/Contents/Resources/DWARF/fat-test.arm.dylib | FileCheck %s
+# RUN: dsymutil -u %t.dSYM -o %t1.dSYM
+# RUN: llvm-dwarfdump -a -v %t1.dSYM/Contents/Resources/DWARF/fat-test.arm.dylib | FileCheck %s
+
+CHECK: /Contents/Resources/DWARF/fat-test.arm.dylib(armv7): file format Mach-O arm
+
+CHECK: .debug_info contents:
+CHECK:  Compile Unit: length = 0x00000034, format = DWARF32, version = 0x0002, abbr_offset = 0x0000, addr_size = 0x04 (next unit at 0x00000038)
+CHECK:  DW_TAG_compile_unit [1] *
+CHECK:    DW_AT_producer [DW_FORM_strp] ( .debug_str[0x00000001] = "clang version 3.8.0 (trunk 243776)")
+CHECK:    DW_AT_language [DW_FORM_data2]  (DW_LANG_C99)
+CHECK:    DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000024] = "fat-test.c")
+CHECK:    DW_AT_stmt_list [DW_FORM_data4] (0x00000000)
+CHECK:    DW_AT_comp_dir [DW_FORM_strp] ( .debug_str[0x0000002f] = "/Inputs")
+CHECK:    DW_TAG_variable [2]
+CHECK:      DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000037] = "armv7_var")
+CHECK:      DW_AT_type [DW_FORM_ref4] (cu + 0x0030 => {0x00000030}
+CHECK:      DW_AT_external [DW_FORM_flag] (0x01)
+CHECK:      DW_AT_decl_file [DW_FORM_data1] ("/Inputs/fat-test.c")
+CHECK:      DW_AT_decl_line [DW_FORM_data1] (23)
+CHECK:      DW_AT_location [DW_FORM_block1] (DW_OP_addr 0x1000)
+CHECK:    DW_TAG_base_type [3]
+CHECK:      DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000041] = "int")
+CHECK:      DW_AT_encoding [DW_FORM_data1]  (DW_ATE_signed)
+CHECK:      DW_AT_byte_size [DW_FORM_data1] (0x04)
+CHECK:    NULL
+
+
+CHECK: .debug_line contents:
+CHECK: Line table prologue:
+CHECK:     total_length: 0x0000002a
+CHECK:          version: 2
+CHECK:  prologue_length: 0x00000021
+CHECK:  min_inst_length: 1
+CHECK:  default_is_stmt: 1
+CHECK:        line_base: -5
+CHECK:       line_range: 14
+CHECK:      opcode_base: 13
+
+CHECK: .apple_names contents:
+CHECK: String: 0x00000037 "armv7_var"
+CHECK-NEXT: Data 0 [
+CHECK-NEXT:   Atom[0]: 0x0000001e
+CHECK-NEXT: ]
+
+CHECK: .apple_types contents:
+CHECK: String: 0x00000041 "int"
+CHECK-NEXT: Data 0 [
+CHECK-NEXT:   Atom[0]: 0x00000030
+CHECK-NEXT:   Atom[1]: 0x0024
+CHECK-NEXT:   Atom[2]: 0x00
+CHECK-NEXT:   Atom[3]: 0x0c3a28a4
+CHECK-NEXT: ]
+
+CHECK: /Contents/Resources/DWARF/fat-test.arm.dylib(armv7s):  file format Mach-O arm
+
+CHECK: .debug_info contents:
+CHECK:  Compile Unit: length = 0x00000034, format = DWARF32, version = 0x0002, abbr_offset = 0x0000, addr_size = 0x04 (next unit at 0x00000038)
+CHECK:  DW_TAG_compile_unit [1] *
+CHECK:    DW_AT_producer [DW_FORM_strp] ( .debug_str[0x00000001] = "clang version 3.8.0 (trunk 243776)")
+CHECK:    DW_AT_language [DW_FORM_data2]  (DW_LANG_C99)
+CHECK:    DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000024] = "fat-test.c")
+CHECK:    DW_AT_stmt_list [DW_FORM_data4] (0x00000000)
+CHECK:    DW_AT_comp_dir [DW_FORM_strp] ( .debug_str[0x0000002f] = "/Inputs")
+CHECK:    DW_TAG_variable [2]
+CHECK:      DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000037] = "armv7s_var")
+CHECK:      DW_AT_type [DW_FORM_ref4] (cu + 0x0030 => {0x00000030}
+CHECK:      DW_AT_external [DW_FORM_flag] (0x01)
+CHECK:      DW_AT_decl_file [DW_FORM_data1] ("/Inputs/fat-test.c")
+CHECK:      DW_AT_decl_line [DW_FORM_data1] (21)
+CHECK:      DW_AT_location [DW_FORM_block1] (DW_OP_addr 0x1000)
+CHECK:    DW_TAG_base_type [3]
+CHECK:      DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000042] = "int")
+CHECK:      DW_AT_encoding [DW_FORM_data1]  (DW_ATE_signed)
+CHECK:      DW_AT_byte_size [DW_FORM_data1] (0x04)
+CHECK:    NULL
+
+CHECK: .debug_line contents:
+CHECK: Line table prologue:
+CHECK:     total_length: 0x0000002a
+CHECK:          version: 2
+CHECK:  prologue_length: 0x00000021
+CHECK:  min_inst_length: 1
+CHECK:  default_is_stmt: 1
+CHECK:        line_base: -5
+CHECK:       line_range: 14
+CHECK:      opcode_base: 13
+
+CHECK: .apple_names contents:
+CHECK: String: 0x00000037 "armv7s_var"
+CHECK-NEXT: Data 0 [
+CHECK-NEXT:   Atom[0]: 0x0000001e
+CHECK-NEXT: ]
+
+CHECK: .apple_types contents:
+CHECK: String: 0x00000042 "int"
+CHECK-NEXT: Data 0 [
+CHECK-NEXT:   Atom[0]: 0x00000030
+CHECK-NEXT:   Atom[1]: 0x0024
+CHECK-NEXT:   Atom[2]: 0x00
+CHECK-NEXT:   Atom[3]: 0x0c3a28a4
+CHECK-NEXT: ]
+
+CHECK: /Contents/Resources/DWARF/fat-test.arm.dylib(arm64): file format Mach-O arm64
+
+CHECK: .debug_info contents:
+CHECK:  Compile Unit: length = 0x00000038, format = DWARF32, version = 0x0002, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x0000003c)
+CHECK:  DW_TAG_compile_unit [1] *
+CHECK:    DW_AT_producer [DW_FORM_strp] ( .debug_str[0x00000001] = "clang version 3.8.0 (trunk 243776)")
+CHECK:    DW_AT_language [DW_FORM_data2]  (DW_LANG_C99)
+CHECK:    DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000024] = "fat-test.c")
+CHECK:    DW_AT_stmt_list [DW_FORM_data4] (0x00000000)
+CHECK:    DW_AT_comp_dir [DW_FORM_strp] ( .debug_str[0x0000002f] = "/Inputs")
+CHECK:    DW_TAG_variable [2]
+CHECK:      DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000037] = "arm64_var")
+CHECK:      DW_AT_type [DW_FORM_ref4] (cu + 0x0034 => {0x00000034}
+CHECK:      DW_AT_external [DW_FORM_flag] (0x01)
+CHECK:      DW_AT_decl_file [DW_FORM_data1] ("/Inputs/fat-test.c")
+CHECK:      DW_AT_decl_line [DW_FORM_data1] (25)
+CHECK:      DW_AT_location [DW_FORM_block1] (DW_OP_addr 0x4000)
+CHECK:    DW_TAG_base_type [3]
+CHECK:      DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000041] = "int")
+CHECK:      DW_AT_encoding [DW_FORM_data1]  (DW_ATE_signed)
+CHECK:      DW_AT_byte_size [DW_FORM_data1] (0x04)
+CHECK:    NULL
+
+CHECK: .debug_line contents:
+CHECK: Line table prologue:
+CHECK:     total_length: 0x0000002a
+CHECK:          version: 2
+CHECK:  prologue_length: 0x00000021
+CHECK:  min_inst_length: 1
+CHECK:  default_is_stmt: 1
+CHECK:        line_base: -5
+CHECK:       line_range: 14
+CHECK:      opcode_base: 13
+
+CHECK: .apple_names contents:
+CHECK: String: 0x00000037 "arm64_var"
+CHECK-NEXT: Data 0 [
+CHECK-NEXT:   Atom[0]: 0x0000001e
+CHECK-NEXT: ]
+
+CHECK: .apple_types contents:
+CHECK: String: 0x00000041 "int"
+CHECK-NEXT: Data 0 [
+CHECK-NEXT:   Atom[0]: 0x00000034
+CHECK-NEXT:   Atom[1]: 0x0024
+CHECK-NEXT:   Atom[2]: 0x00
+CHECK-NEXT:   Atom[3]: 0x0c3a28a4
+CHECK-NEXT: ]