Various crash reporting tools have a problem with the dwarf generated for

assembly source when it generates the TAG_subprogram dwarf debug info for
the labels that have nothing between them as in this bit of assembly source:

% cat ZeroLength.s
_func1:
_func2:
 nop

One solution would be to not emit the subsequent labels with the same address
and use the next label with a different address or the end of the section for
the AT_high_pc value of the TAG_subprogram.

Turns out in llvm-mc it is not possible in all cases to determine of two
symbols have the same value at the point we put out the TAG_subprogram dwarf
debug info.

So we will have llvm-mc instead of putting out TAG_subprogram's put out
DW_TAG_label's.  And the DW_TAG_label does not have a AT_high_pc value which
avoids the problem.

This commit is only the functional change to make the diffs clear as to what is
really being changed.  The next commit will be to clean up the names of such
things like MCGenDwarfSubprogramEntry to something like MCGenDwarfLabelEntry.

rdar://10666925

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147860 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 986b8b67df5d0ffb142c0449afc3cab0fca3f16f..83fa0690e95781d354cf40728c5c8b44ff9650ed 100644 (file)
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -454,15 +454,14 @@ static void EmitGenDwarfAbbrev(MCStreamer *MCOS) {
   EmitAbbrev(MCOS, dwarf::DW_AT_language, dwarf::DW_FORM_data2);
   EmitAbbrev(MCOS, 0, 0);
 
-  // DW_TAG_subprogram DIE abbrev (2).
+  // DW_TAG_label DIE abbrev (2).
   MCOS->EmitULEB128IntValue(2);
-  MCOS->EmitULEB128IntValue(dwarf::DW_TAG_subprogram);
+  MCOS->EmitULEB128IntValue(dwarf::DW_TAG_label);
   MCOS->EmitIntValue(dwarf::DW_CHILDREN_yes, 1);
   EmitAbbrev(MCOS, dwarf::DW_AT_name, dwarf::DW_FORM_string);
   EmitAbbrev(MCOS, dwarf::DW_AT_decl_file, dwarf::DW_FORM_data4);
   EmitAbbrev(MCOS, dwarf::DW_AT_decl_line, dwarf::DW_FORM_data4);
   EmitAbbrev(MCOS, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr);
-  EmitAbbrev(MCOS, dwarf::DW_AT_high_pc, dwarf::DW_FORM_addr);
   EmitAbbrev(MCOS, dwarf::DW_AT_prototyped, dwarf::DW_FORM_flag);
   EmitAbbrev(MCOS, 0, 0);
 
@@ -545,7 +544,7 @@ static void EmitGenDwarfAranges(MCStreamer *MCOS) {
 
 // When generating dwarf for assembly source files this emits the data for
 // .debug_info section which contains three parts.  The header, the compile_unit
-// DIE and a list of subprogram DIEs.
+// DIE and a list of label DIEs.
 static void EmitGenDwarfInfo(MCStreamer *MCOS) {
   MCContext &context = MCOS->getContext();
 
@@ -630,7 +629,7 @@ static void EmitGenDwarfInfo(MCStreamer *MCOS) {
   // draft has no standard code for assembler.
   MCOS->EmitIntValue(dwarf::DW_LANG_Mips_Assembler, 2);
 
-  // Third part: the list of subprogram DIEs.
+  // Third part: the list of label DIEs.
 
   // Loop on saved info for dwarf subprograms and create the DIEs for them.
   const std::vector<const MCGenDwarfSubprogramEntry *> &Entries =
@@ -640,7 +639,7 @@ static void EmitGenDwarfInfo(MCStreamer *MCOS) {
        ++it) {
     const MCGenDwarfSubprogramEntry *Entry = *it;
 
-    // The DW_TAG_subprogram DIE abbrev (2).
+    // The DW_TAG_label DIE abbrev (2).
     MCOS->EmitULEB128IntValue(2);
 
     // AT_name, of the label without any leading underbar.
@@ -658,17 +657,6 @@ static void EmitGenDwarfInfo(MCStreamer *MCOS) {
                                              MCSymbolRefExpr::VK_None, context);
     MCOS->EmitAbsValue(AT_low_pc, AddrSize);
 
-    // AT_high_pc, end address which is the next label or end of the section.
-    std::vector<const MCGenDwarfSubprogramEntry *>::const_iterator next = it+1;
-    if (next != Entries.end()){
-      const MCGenDwarfSubprogramEntry *NextEntry = *next;
-      const MCExpr *AT_high_pc = MCSymbolRefExpr::Create(NextEntry->getLabel(),
-                                             MCSymbolRefExpr::VK_None, context);
-      MCOS->EmitAbsValue(AT_high_pc, AddrSize);
-    } else {
-      MCOS->EmitAbsValue(End, AddrSize);
-    }
-
     // DW_AT_prototyped, a one byte flag value of 0 saying we have no prototype.
     MCOS->EmitIntValue(0, 1);
 

diff --git a/test/MC/MachO/gen-dwarf.s b/test/MC/MachO/gen-dwarf.s
index a443d75ae070de846cfe17386b4d6d9cecb95ae6..4fbc32d295b71d76d585a3c76a2872c62cfeff9f 100644 (file)
--- a/test/MC/MachO/gen-dwarf.s
+++ b/test/MC/MachO/gen-dwarf.s
@@ -7,6 +7,7 @@ _bar:
 L1:    leave
        ret
 _foo:
+_baz:
        nop
 .data
 _x:    .long 1
@@ -24,12 +25,11 @@ _x: .long 1
 // CHECK:      DW_AT_producer  DW_FORM_string
 // CHECK:      DW_AT_language  DW_FORM_data2
 
-// CHECK: [2] DW_TAG_subprogram        DW_CHILDREN_yes
+// CHECK: [2] DW_TAG_label     DW_CHILDREN_yes
 // CHECK:      DW_AT_name      DW_FORM_string
 // CHECK:      DW_AT_decl_file DW_FORM_data4
 // CHECK:      DW_AT_decl_line DW_FORM_data4
 // CHECK:      DW_AT_low_pc    DW_FORM_addr
-// CHECK:      DW_AT_high_pc   DW_FORM_addr
 // CHECK:      DW_AT_prototyped        DW_FORM_flag
 
 // CHECK: [3] DW_TAG_unspecified_parameters    DW_CHILDREN_no
@@ -48,24 +48,33 @@ _x: .long 1
 // CHECK:    DW_AT_producer [DW_FORM_string]   ("llvm-mc (based on {{.*}})")
 // CHECK:    DW_AT_language [DW_FORM_data2]    (0x8001)
 
-// CHECK:    DW_TAG_subprogram [2] *
+// CHECK:    DW_TAG_label [2] *
 // CHECK:      DW_AT_name [DW_FORM_string]     ("bar")
 // CHECK:      DW_AT_decl_file [DW_FORM_data4] (0x00000001)
 // CHECK:      DW_AT_decl_line [DW_FORM_data4] (0x00000005)
 // CHECK:      DW_AT_low_pc [DW_FORM_addr]     (0x0000000000000000)
-// CHECK:      DW_AT_high_pc [DW_FORM_addr]    (0x0000000000000007)
 // CHECK:      DW_AT_prototyped [DW_FORM_flag] (0x00)
 
 // CHECK:      DW_TAG_unspecified_parameters [3]  
 
 // CHECK:      NULL
 
-// CHECK:    DW_TAG_subprogram [2] *
+// CHECK:    DW_TAG_label [2] *
 // CHECK:      DW_AT_name [DW_FORM_string]     ("foo")
 // CHECK:      DW_AT_decl_file [DW_FORM_data4] (0x00000001)
 // CHECK:      DW_AT_decl_line [DW_FORM_data4] (0x00000009)
 // CHECK:      DW_AT_low_pc [DW_FORM_addr]     (0x0000000000000007)
-// CHECK:      DW_AT_high_pc [DW_FORM_addr]    (0x0000000000000008)
+// CHECK:      DW_AT_prototyped [DW_FORM_flag] (0x00)
+
+// CHECK:      DW_TAG_unspecified_parameters [3]  
+
+// CHECK:      NULL
+
+// CHECK:    DW_TAG_label [2] *
+// CHECK:      DW_AT_name [DW_FORM_string]     ("baz")
+// CHECK:      DW_AT_decl_file [DW_FORM_data4] (0x00000001)
+// CHECK:      DW_AT_decl_line [DW_FORM_data4] (0x0000000a)
+// CHECK:      DW_AT_low_pc [DW_FORM_addr]     (0x0000000000000007)
 // CHECK:      DW_AT_prototyped [DW_FORM_flag] (0x00)
 
 // CHECK:      DW_TAG_unspecified_parameters [3]  
@@ -109,5 +118,5 @@ _x: .long 1
 // CHECK: 0x0000000000000000      6      0      1   0  is_stmt
 // CHECK: 0x0000000000000005      7      0      1   0  is_stmt
 // CHECK: 0x0000000000000006      8      0      1   0  is_stmt
-// CHECK: 0x0000000000000007     10      0      1   0  is_stmt
-// CHECK: 0x0000000000000008     10      0      1   0  is_stmt end_sequence
+// CHECK: 0x0000000000000007     11      0      1   0  is_stmt
+// CHECK: 0x0000000000000008     11      0      1   0  is_stmt end_sequence