[lldb][DWARF] Sort ranges list in dwarf 5.

[ZequanWu]

Dwarf 5 says "There is no requirement that the entries be ordered in any particular way" in 2.17.3 Non-Contiguous Address Ranges for rnglist. Some places assume the ranges are already sorted but it's not.

For example, when parsing function info, it validates low and hi address of the function: GetMinRangeBase returns the first range entry base and GetMaxRangeEnd returns the last range end. If low >= hi, it stops parsing this function. This causes missing inline stack frames for those functions.

This change fixes it and updates the test lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s so that two ranges in .debug_rnglists are out of order and image lookup -v -s lookup_rnglists is still able to produce sorted ranges for the inner block.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Zequan Wu (ZequanWu)

Changes

Dwarf 5 says "There is no requirement that the entries be ordered in any particular way" in 2.17.3 Non-Contiguous Address Ranges for rnglist. Some places assume the ranges are already sorted but it's not. This fixes it.

---

Full diff: https://github.com/llvm/llvm-project/pull/91343.diff

2 Files Affected:

• (modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp (+1)
• (modified) lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s (+3-3)

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
index dabc595427df..3a57ec970b07 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
@@ -1062,6 +1062,7 @@ DWARFUnit::FindRnglistFromOffset(dw_offset_t offset) {
     ranges.Append(DWARFRangeList::Entry(llvm_range.LowPC,
                                         llvm_range.HighPC - llvm_range.LowPC));
   }
+  ranges.Sort();
   return ranges;
 }
 
diff --git a/lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s b/lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s
index 89b5d94c68c3..af8a1796f3ab 100644
--- a/lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s
+++ b/lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s
@@ -124,12 +124,12 @@ lookup_rnglists2:
 .Lrnglists_table_base0:
         .long   .Ldebug_ranges0-.Lrnglists_table_base0
 .Ldebug_ranges0:
-        .byte   4                       # DW_RLE_offset_pair
-        .uleb128 .Lblock1_begin-rnglists  #   starting offset
-        .uleb128 .Lblock1_end-rnglists    #   ending offset
         .byte   4                       # DW_RLE_offset_pair
         .uleb128 .Lblock2_begin-rnglists  #   starting offset
         .uleb128 .Lblock2_end-rnglists    #   ending offset
+        .byte   4                       # DW_RLE_offset_pair
+        .uleb128 .Lblock1_begin-rnglists  #   starting offset
+        .uleb128 .Lblock1_end-rnglists    #   ending offset
         .byte   0                       # DW_RLE_end_of_list
 .Ldebug_rnglist_table_end0:
 

[bulbazord]

Some places assume the ranges are already sorted but it's not. This fixes it.

What places assumed it was sorted? I assume this means there are some bugs that this fixes? Can you give some more details about how you came to write this patch?

[ZequanWu]

Some places assume the ranges are already sorted but it's not. This fixes it.

What places assumed it was sorted? I assume this means there are some bugs that this fixes? Can you give some more details about how you came to write this patch?

For example: https://github.com/llvm/llvm-project/blob/main/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp#L922-L927.
When parsing function info, it validates low and hi address of the function: GetMinRangeBase returns the first range entry base and GetMaxRangeEnd returns the last range end. If low >= hi, it stops parsing this function.

This causes missing inline stack frames for us when debugging a core dump.

[bulbazord]

For example: https://github.com/llvm/llvm-project/blob/main/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp#L922-L927. When parsing function info, it validates low and hi address of the function: GetMinRangeBase returns the first range entry base and GetMaxRangeEnd returns the last range end. If low >= hi, it stops parsing this function.

This causes missing inline stack frames for us when debugging a core dump.

Gotcha, makes sense. Since you know how this fails, could you add a test to make sure that scenario continues working?

[ZequanWu]

For example: https://github.com/llvm/llvm-project/blob/main/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp#L922-L927. When parsing function info, it validates low and hi address of the function: GetMinRangeBase returns the first range entry base and GetMaxRangeEnd returns the last range end. If low >= hi, it stops parsing this function.
This causes missing inline stack frames for us when debugging a core dump.

Gotcha, makes sense. Since you know how this fails, could you add a test to make sure that scenario continues working?

Yeah, I updated the test lldb/test/Shell/SymbolFile/DWARF/x86/debug_rnglists.s so that two ranges in .debug_rnglists are out of order and image lookup -v -s lookup_rnglists is still able to produce sorted ranges for the inner block:
Without this change:

         Blocks: id = {0x00000030}, range = [0x00000000-0x00000004)
         Symbol: id = {0x00000003}, range = [0x0000000000000001-0x0000000000000004), name="lookup_rnglists"

With this change:

         Blocks: id = {0x00000030}, range = [0x00000000-0x00000004)
                 id = {0x00000046}, ranges = [0x00000001-0x00000002)[0x00000003-0x00000004)
         Symbol: id = {0x00000003}, range = [0x0000000000000001-0x0000000000000004), name="lookup_rnglists"

[bulbazord]

LGTM