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[lldb/DWARF] Fix DW_AT_addr_base & DW_AT_low_pc interaction
In DWARF5 DW_AT_low_pc (and DW_AT_entry_pc, and possibly others) can use DW_FORM_addrx to refer to the address indirectly. This means we need to have processed the DW_AT_addr_base attribute before we can do anything with these. Since we were processing the unit attributes serially, this created a problem in cases where the DW_AT_addr_base comes after DW_AT_low_pc -- we would end up computing the wrong unit base address, which also corrupted any values which later depended on that (for instance range lists). Clang currently always emits DW_AT_addr_base last. The fix is simple -- process DW_AT_addr_base first, regardless of its position in the attribute list.
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lines changed

2 files changed

+119
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lines changed

‎lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp‎

Lines changed: 13 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -287,16 +287,25 @@ void DWARFUnit::AddUnitDIE(const DWARFDebugInfoEntry &cu_die) {
287287

288288
DWARFAttributes attributes;
289289
size_t num_attributes = cu_die.GetAttributes(this, attributes);
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// Extract DW_AT_addr_base first, as other attributes may need it.
292+
for (size_t i = 0; i < num_attributes; ++i) {
293+
if (attributes.AttributeAtIndex(i) != DW_AT_addr_base)
294+
continue;
295+
DWARFFormValue form_value;
296+
if (attributes.ExtractFormValueAtIndex(i, form_value)) {
297+
addr_base = form_value.Unsigned();
298+
SetAddrBase(*addr_base);
299+
break;
300+
}
301+
}
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290303
for (size_t i = 0; i < num_attributes; ++i) {
291304
dw_attr_t attr = attributes.AttributeAtIndex(i);
292305
DWARFFormValue form_value;
293306
if (!attributes.ExtractFormValueAtIndex(i, form_value))
294307
continue;
295308
switch (attr) {
296-
case DW_AT_addr_base:
297-
addr_base = form_value.Unsigned();
298-
SetAddrBase(*addr_base);
299-
break;
300309
case DW_AT_rnglists_base:
301310
ranges_base = form_value.Unsigned();
302311
SetRangesBase(*ranges_base);

‎lldb/test/Shell/SymbolFile/DWARF/DW_AT_low_pc-addrx.s‎

Lines changed: 106 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,106 @@
1+
# REQUIRES: x86
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# RUN: llvm-mc -triple=x86_64-pc-linux -filetype=obj %s > %t
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# RUN: %lldb %t -o "image lookup -v -s lookup_rnglists" \
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# RUN: -o exit | FileCheck %s
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# CHECK-LABEL: image lookup -v -s lookup_rnglists
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# CHECK: Function: id = {0x7fffffff0000002d}, name = "rnglists", range = [0x0000000000000000-0x0000000000000003)
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# CHECK: Blocks: id = {0x7fffffff0000002d}, range = [0x00000000-0x00000003)
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# CHECK-NEXT: id = {0x7fffffff00000043}, range = [0x00000001-0x00000002)
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.text
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rnglists:
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nop
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.Lblock1_begin:
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lookup_rnglists:
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nop
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.Lblock1_end:
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nop
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.Lrnglists_end:
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.section .debug_abbrev,"",@progbits
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.byte 1 # Abbreviation Code
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.byte 17 # DW_TAG_compile_unit
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.byte 1 # DW_CHILDREN_yes
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.byte 37 # DW_AT_producer
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.byte 8 # DW_FORM_string
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.byte 17 # DW_AT_low_pc
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.byte 27 # DW_FORM_addrx
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.byte 18 # DW_AT_high_pc
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.byte 6 # DW_FORM_data4
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.byte 116 # DW_AT_rnglists_base
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.byte 23 # DW_FORM_sec_offset
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.byte 115 # DW_AT_addr_base
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.byte 23 # DW_FORM_sec_offset
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 2 # Abbreviation Code
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.byte 46 # DW_TAG_subprogram
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.byte 1 # DW_CHILDREN_yes
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.byte 17 # DW_AT_low_pc
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.byte 1 # DW_FORM_addr
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.byte 18 # DW_AT_high_pc
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.byte 6 # DW_FORM_data4
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.byte 3 # DW_AT_name
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.byte 8 # DW_FORM_string
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 5 # Abbreviation Code
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.byte 11 # DW_TAG_lexical_block
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.byte 0 # DW_CHILDREN_no
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.byte 85 # DW_AT_ranges
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.byte 35 # DW_FORM_rnglistx
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 0 # EOM(3)
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.section .debug_info,"",@progbits
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.Lcu_begin0:
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.long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
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.Ldebug_info_start0:
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.short 5 # DWARF version number
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.byte 1 # DWARF Unit Type
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.byte 8 # Address Size (in bytes)
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.long .debug_abbrev # Offset Into Abbrev. Section
66+
.byte 1 # Abbrev [1] 0xc:0x5f DW_TAG_compile_unit
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.asciz "Hand-written DWARF" # DW_AT_producer
68+
.byte 0 # DW_AT_low_pc
69+
.long .Lrnglists_end-rnglists # DW_AT_high_pc
70+
.long .Lrnglists_table_base0 # DW_AT_rnglists_base
71+
.long .Laddr_table_base0 # DW_AT_addr_base
72+
.byte 2 # Abbrev [2] 0x2b:0x37 DW_TAG_subprogram
73+
.quad rnglists # DW_AT_low_pc
74+
.long .Lrnglists_end-rnglists # DW_AT_high_pc
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.asciz "rnglists" # DW_AT_name
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.byte 5 # Abbrev [5] 0x52:0xf DW_TAG_lexical_block
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.byte 0 # DW_AT_ranges
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.byte 0 # End Of Children Mark
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.byte 0 # End Of Children Mark
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.Ldebug_info_end0:
81+
82+
.section .debug_addr,"",@progbits
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.long .Ldebug_addr_end0-.Ldebug_addr_start0 # Length of contribution
84+
.Ldebug_addr_start0:
85+
.short 5 # DWARF version number
86+
.byte 8 # Address size
87+
.byte 0 # Segment selector size
88+
.Laddr_table_base0:
89+
.quad rnglists
90+
.Ldebug_addr_end0:
91+
92+
.section .debug_rnglists,"",@progbits
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.long .Ldebug_rnglist_table_end0-.Ldebug_rnglist_table_start0 # Length
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.Ldebug_rnglist_table_start0:
95+
.short 5 # Version
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.byte 8 # Address size
97+
.byte 0 # Segment selector size
98+
.long 1 # Offset entry count
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.Lrnglists_table_base0:
100+
.long .Ldebug_ranges0-.Lrnglists_table_base0
101+
.Ldebug_ranges0:
102+
.byte 4 # DW_RLE_offset_pair
103+
.uleb128 .Lblock1_begin-rnglists # starting offset
104+
.uleb128 .Lblock1_end-rnglists # ending offset
105+
.byte 0 # DW_RLE_end_of_list
106+
.Ldebug_rnglist_table_end0:

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