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clang-p2996/lldb/test/Shell/SymbolFile/DWARF/debug_loc.s
Pavel Labath 7cfa74fc69 [lldb/DWARF] Trust CU DW_AT_low/high_pc information when building address tables 
Summary:
The code in DWARFCompileUnit::BuildAddressRangeTable tries hard to avoid
relying on DW_AT_low/high_pc for compile unit range information, and
this logic is a big cause of llvm/lldb divergence in the lowest layers
of dwarf parsing code.

The implicit assumption in that code is that this information (as opposed to
DW_AT_ranges) is unreliable. However, I have not been able to verify
that assumption. It is definitely not true for all present-day
compilers (gcc, clang, icc), and it was also not the case for the
historic compilers that I have been able to get a hold of (thanks Matt
Godbolt).

All compiler included in my research either produced correct
DW_AT_ranges or .debug_aranges entries, or they produced no DW_AT_hi/lo
pc at all. The detailed findings are:
- gcc >= 4.4: produces DW_AT_ranges and .debug_aranges
- 4.1 <= gcc < 4.4: no DW_AT_ranges, no DW_AT_high_pc, .debug_aranges
  present. The upper version range here is uncertain as godbolt.org does
  not have intermediate versions.
- gcc < 4.1: no versions on godbolt.org
- clang >= 3.5: produces DW_AT_ranges, and (optionally) .debug_aranges
- 3.4 <= clang < 3.5: no DW_AT_ranges, no DW_AT_high_pc, .debug_aranges
  present.
- clang <= 3.3: no DW_AT_ranges, no DW_AT_high_pc, no .debug_aranges
- icc >= 16.0.1: produces DW_AT_ranges
- icc < 16.0.1: no functional versions on godbolt.org (some are present
  but fail to compile)

Based on this analysis, I believe it is safe to start trusting
DW_AT_low/high_pc information in dwarf as well as remove the code for
manually reconstructing range information by traversing the DIE
structure, and just keep the line table fallback. The only compilers
where this will change behavior are pre-3.4 clangs, which are almost 7
years old now. However, the functionality should remain unchanged
because we will be able to reconstruct this information from the line
table, which seems to be needed for some line-tables-only scenarios
anyway (haven't researched this too much, but at least some compilers
seem to emit DW_AT_ranges even in these situations).

In addition, benchmarks showed that for these compilers computing the
ranges via line tables is noticably faster than doing so via the DIE
tree.

Other advantages include simplifying the code base, removing some
untested code (the only test changes are recent tests with overly
reduced synthetic dwarf), and increasing llvm convergence.

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D78489
2020-04-23 16:12:41 +02:00

254 lines
9.9 KiB
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# Test location list handling, including the cases of invalid input. The exact
# behavior in the invalid cases is not particularly important, but it should be
# "reasonable".
# REQUIRES: x86
# UNSUPPORTED: lldb-repro
# RUN: llvm-mc -triple=x86_64-pc-linux -filetype=obj %s --defsym LOC=0 > %t
# RUN: %lldb %t -o "image lookup -v -a 0" -o "image lookup -v -a 2" \
# RUN: -o "image dump symfile" -o exit | FileCheck %s
# RUN: llvm-mc -triple=x86_64-pc-linux -filetype=obj %s --defsym LOCLISTS=0 > %t
# RUN: %lldb %t -o "image lookup -v -a 0" -o "image lookup -v -a 2" \
# RUN: -o "image dump symfile" -o exit | FileCheck %s --check-prefix=CHECK --check-prefix=LOCLISTS
# CHECK-LABEL: image lookup -v -a 0
# CHECK: Variable: {{.*}}, name = "x0", type = "int", location = DW_OP_reg5 RDI,
# CHECK: Variable: {{.*}}, name = "x1", type = "int", location = ,
# CHECK-LABEL: image lookup -v -a 2
# CHECK: Variable: {{.*}}, name = "x0", type = "int", location = DW_OP_reg0 RAX,
# CHECK: Variable: {{.*}}, name = "x1", type = "int", location = ,
# CHECK: Variable: {{.*}}, name = "x3", type = "int", location = DW_OP_reg1 RDX,
# CHECK-LABEL: image dump symfile
# CHECK: CompileUnit{0x00000000}
# CHECK: Function{
# CHECK: Variable{{.*}}, name = "x0", {{.*}}, scope = parameter, location =
# CHECK-NEXT: [0x0000000000000000, 0x0000000000000001): DW_OP_reg5 RDI
# CHECK-NEXT: [0x0000000000000001, 0x0000000000000006): DW_OP_reg0 RAX
# CHECK: Variable{{.*}}, name = "x1", {{.*}}, scope = parameter
# CHECK: Variable{{.*}}, name = "x2", {{.*}}, scope = parameter, location = 0x00000000: error: unexpected end of data
# CHECK: Variable{{.*}}, name = "x3", {{.*}}, scope = parameter, location =
# CHECK-NEXT: [0x0000000000000002, 0x0000000000000003): DW_OP_reg1 RDX
# LOCLISTS: Variable{{.*}}, name = "x4", {{.*}}, scope = parameter, location =
# LOCLISTS-NEXT: DW_LLE_startx_length (0x000000000000dead, 0x0000000000000001): DW_OP_reg2 RCX
.ifdef LOC
.macro OFFSET_PAIR lo hi
.quad \lo
.quad \hi
.endm
.macro BASE_ADDRESS base
.quad -1
.quad \base
.endm
.macro EXPR_SIZE sz
.short \sz
.endm
.macro END_OF_LIST
.quad 0
.quad 0
.endm
.endif
.ifdef LOCLISTS
.macro OFFSET_PAIR lo hi
.byte 4 # DW_LLE_offset_pair
.uleb128 \lo
.uleb128 \hi
.endm
.macro BASE_ADDRESS base
.byte 6 # DW_LLE_base_address
.quad \base
.endm
.macro EXPR_SIZE sz
.uleb128 \sz
.endm
.macro END_OF_LIST
.byte 0 # DW_LLE_end_of_list
.endm
.endif
.type f,@function
f: # @f
.Lfunc_begin0:
nop
.Ltmp0:
nop
.Ltmp1:
nop
.Ltmp2:
nop
.Ltmp3:
nop
.Ltmp4:
nop
.Lfunc_end0:
.size f, .Lfunc_end0-f
.section .debug_str,"MS",@progbits,1
.Linfo_string0:
.asciz "Hand-written DWARF"
.Linfo_string3:
.asciz "f"
.Linfo_string4:
.asciz "int"
.ifdef LOC
.section .debug_loc,"",@progbits
.endif
.ifdef LOCLISTS
.section .debug_loclists,"",@progbits
.long .Ldebug_loclist_table_end0-.Ldebug_loclist_table_start0 # Length
.Ldebug_loclist_table_start0:
.short 5 # Version
.byte 8 # Address size
.byte 0 # Segment selector size
.long 0 # Offset entry count
.endif
.Ldebug_loc0:
OFFSET_PAIR .Lfunc_begin0-.Lfunc_begin0, .Ltmp0-.Lfunc_begin0
EXPR_SIZE 1
.byte 85 # super-register DW_OP_reg5
OFFSET_PAIR .Ltmp0-.Lfunc_begin0, .Lfunc_end0-.Lfunc_begin0
EXPR_SIZE 1
.byte 80 # super-register DW_OP_reg0
END_OF_LIST
.Ldebug_loc3:
BASE_ADDRESS .Ltmp1
OFFSET_PAIR .Ltmp1-.Ltmp1, .Ltmp2-.Ltmp1
EXPR_SIZE 1
.byte 81 # super-register DW_OP_reg1
END_OF_LIST
.ifdef LOCLISTS
.Ldebug_loc4:
.byte 3 # DW_LLE_startx_length
.uleb128 0xdead
.uleb128 1
EXPR_SIZE 1
.byte 82 # super-register DW_OP_reg2
END_OF_LIST
.endif
.Ldebug_loc2:
OFFSET_PAIR .Lfunc_begin0-.Lfunc_begin0, .Lfunc_end0-.Lfunc_begin0
EXPR_SIZE 0xdead
.Ldebug_loclist_table_end0:
.section .debug_abbrev,"",@progbits
.byte 1 # Abbreviation Code
.byte 17 # DW_TAG_compile_unit
.byte 1 # DW_CHILDREN_yes
.byte 37 # DW_AT_producer
.byte 14 # DW_FORM_strp
.byte 19 # DW_AT_language
.byte 5 # DW_FORM_data2
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 18 # DW_AT_high_pc
.byte 6 # DW_FORM_data4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 1 # DW_CHILDREN_yes
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 18 # DW_AT_high_pc
.byte 6 # DW_FORM_data4
.byte 3 # DW_AT_name
.byte 14 # DW_FORM_strp
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 3 # Abbreviation Code
.byte 5 # DW_TAG_formal_parameter
.byte 0 # DW_CHILDREN_no
.byte 2 # DW_AT_location
.byte 23 # DW_FORM_sec_offset
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 4 # Abbreviation Code
.byte 36 # DW_TAG_base_type
.byte 0 # DW_CHILDREN_no
.byte 3 # DW_AT_name
.byte 14 # DW_FORM_strp
.byte 62 # DW_AT_encoding
.byte 11 # DW_FORM_data1
.byte 11 # DW_AT_byte_size
.byte 11 # DW_FORM_data1
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 0 # EOM(3)
.section .debug_info,"",@progbits
.Lcu_begin0:
.long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
.Ldebug_info_start0:
.ifdef LOC
.short 4 # DWARF version number
.long .debug_abbrev # Offset Into Abbrev. Section
.byte 8 # Address Size (in bytes)
.endif
.ifdef LOCLISTS
.short 5 # DWARF version number
.byte 1 # DWARF Unit Type
.byte 8 # Address Size (in bytes)
.long .debug_abbrev # Offset Into Abbrev. Section
.endif
.byte 1 # Abbrev [1] 0xb:0x50 DW_TAG_compile_unit
.long .Linfo_string0 # DW_AT_producer
.short 12 # DW_AT_language
.quad .Lfunc_begin0 # DW_AT_low_pc
.long .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
.byte 2 # Abbrev [2] 0x2a:0x29 DW_TAG_subprogram
.quad .Lfunc_begin0 # DW_AT_low_pc
.long .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
.long .Linfo_string3 # DW_AT_name
.long .Lint # DW_AT_type
.byte 3 # Abbrev [3] DW_TAG_formal_parameter
.long .Ldebug_loc0 # DW_AT_location
.asciz "x0" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.byte 3 # Abbrev [3] DW_TAG_formal_parameter
.long 0xdeadbeef # DW_AT_location
.asciz "x1" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.byte 3 # Abbrev [3] DW_TAG_formal_parameter
.long .Ldebug_loc2 # DW_AT_location
.asciz "x2" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.byte 3 # Abbrev [3] DW_TAG_formal_parameter
.long .Ldebug_loc3 # DW_AT_location
.asciz "x3" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.ifdef LOCLISTS
.byte 3 # Abbrev [3] DW_TAG_formal_parameter
.long .Ldebug_loc4 # DW_AT_location
.asciz "x4" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.endif
.byte 0 # End Of Children Mark
.Lint:
.byte 4 # Abbrev [4] 0x53:0x7 DW_TAG_base_type
.long .Linfo_string4 # DW_AT_name
.byte 5 # DW_AT_encoding
.byte 4 # DW_AT_byte_size
.byte 0 # End Of Children Mark
.Ldebug_info_end0:
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