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[lldb] Improve unwinding for discontinuous functions #111409

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Oct 14, 2024
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[lldb] Improve unwinding for discontinuous functions #111409

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4 changes: 3 additions & 1 deletion lldb/source/Commands/CommandObjectTarget.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3583,10 +3583,12 @@ class CommandObjectTargetModulesShowUnwind : public CommandObjectParsed {
addr_t start_addr = range.GetBaseAddress().GetLoadAddress(target);
if (abi)
start_addr = abi->FixCodeAddress(start_addr);
range.GetBaseAddress().SetLoadAddress(start_addr, target);

FuncUnwindersSP func_unwinders_sp(
sc.module_sp->GetUnwindTable()
.GetUncachedFuncUnwindersContainingAddress(start_addr, sc));
.GetUncachedFuncUnwindersContainingAddress(range.GetBaseAddress(),
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This is because image show-unwind wouldn't use the eh_frame address range without it (it requires a resolved address).

BTW. This would have been easier to investigate (and test) if this command used the actual cached unwind plans instead of creating them from scratch. This way I was left puzzled as to unwind went off track even though the unwind plans looked (mostly) reasonable. What would you say to:
a) adding an option to use/print the cached plans
b) making this option the default
c) deleting the non-cached option entirely?

sc));
if (!func_unwinders_sp)
continue;

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12 changes: 6 additions & 6 deletions lldb/source/Symbol/UnwindTable.cpp
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Expand Up @@ -99,12 +99,6 @@ UnwindTable::GetAddressRange(const Address &addr, const SymbolContext &sc) {
m_object_file_unwind_up->GetAddressRange(addr, range))
return range;

// Check the symbol context
if (sc.GetAddressRange(eSymbolContextFunction | eSymbolContextSymbol, 0,
false, range) &&
range.GetBaseAddress().IsValid())
return range;

// Does the eh_frame unwind info has a function bounds for this addr?
if (m_eh_frame_up && m_eh_frame_up->GetAddressRange(addr, range))
return range;
Expand All @@ -113,6 +107,12 @@ UnwindTable::GetAddressRange(const Address &addr, const SymbolContext &sc) {
if (m_debug_frame_up && m_debug_frame_up->GetAddressRange(addr, range))
return range;

// Check the symbol context
if (sc.GetAddressRange(eSymbolContextFunction | eSymbolContextSymbol, 0,
false, range) &&
range.GetBaseAddress().IsValid())
return range;

return std::nullopt;
}

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256 changes: 256 additions & 0 deletions lldb/test/Shell/Unwind/Inputs/basic-block-sections-with-dwarf.s
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@@ -0,0 +1,256 @@
# An example of a function which has been split into two parts. Roughly
# corresponds to this C code.
# int baz() { return 47; }
# int bar() { return foo(0); }
# int foo(int flag) { return flag ? bar() : baz(); }
# int main() { return foo(1); }
# The function bar has been placed "in the middle" of foo.

.text

.type baz,@function
baz:
.cfi_startproc
movl $47, %eax
retq
.cfi_endproc
.Lbaz_end:
.size baz, .Lbaz_end-baz

.type foo,@function
foo:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp
subq $16, %rsp
movl %edi, -8(%rbp)
cmpl $0, -8(%rbp)
je foo.__part.2
jmp foo.__part.1
.cfi_endproc
.Lfoo_end:
.size foo, .Lfoo_end-foo

foo.__part.1:
.cfi_startproc
.cfi_def_cfa %rbp, 16
.cfi_offset %rbp, -16
callq bar
movl %eax, -4(%rbp)
jmp foo.__part.3
.Lfoo.__part.1_end:
.size foo.__part.1, .Lfoo.__part.1_end-foo.__part.1
.cfi_endproc

bar:
.cfi_startproc
# NB: Decrease the stack pointer to make the unwind info for this function
# different from the surrounding foo function.
subq $24, %rsp
.cfi_def_cfa_offset 32
xorl %edi, %edi
callq foo
addq $24, %rsp
.cfi_def_cfa %rsp, 8
retq
.cfi_endproc
.Lbar_end:
.size bar, .Lbar_end-bar

foo.__part.2:
.cfi_startproc
.cfi_def_cfa %rbp, 16
.cfi_offset %rbp, -16
callq baz
movl %eax, -4(%rbp)
jmp foo.__part.3
.Lfoo.__part.2_end:
.size foo.__part.2, .Lfoo.__part.2_end-foo.__part.2
.cfi_endproc

foo.__part.3:
.cfi_startproc
.cfi_def_cfa %rbp, 16
.cfi_offset %rbp, -16
movl -4(%rbp), %eax
addq $16, %rsp
popq %rbp
.cfi_def_cfa %rsp, 8
retq
.Lfoo.__part.3_end:
.size foo.__part.3, .Lfoo.__part.3_end-foo.__part.3
.cfi_endproc


.globl main
.type main,@function
main:
.cfi_startproc
movl $1, %edi
callq foo
retq
.cfi_endproc
.Lmain_end:
.size main, .Lmain_end-main

.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 8 # DW_FORM_string
.byte 19 # DW_AT_language
.byte 5 # DW_FORM_data2
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 85 # DW_AT_ranges
.byte 35 # DW_FORM_rnglistx
.byte 116 # DW_AT_rnglists_base
.byte 23 # DW_FORM_sec_offset
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 0 # DW_CHILDREN_no
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 18 # DW_AT_high_pc
.byte 1 # DW_FORM_addr
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 3 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 1 # DW_CHILDREN_yes
.byte 85 # DW_AT_ranges
.byte 35 # DW_FORM_rnglistx
.byte 64 # DW_AT_frame_base
.byte 24 # DW_FORM_exprloc
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 4 # Abbreviation Code
.byte 5 # DW_TAG_formal_parameter
.byte 0 # DW_CHILDREN_no
.byte 2 # DW_AT_location
.byte 24 # DW_FORM_exprloc
.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 5 # Abbreviation Code
.byte 36 # DW_TAG_base_type
.byte 0 # DW_CHILDREN_no
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.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:
.short 5 # DWARF version number
.byte 1 # DWARF Unit Type
.byte 8 # Address Size (in bytes)
.long .debug_abbrev # Offset Into Abbrev. Section
.byte 1 # Abbrev [1] DW_TAG_compile_unit
.asciz "Hand-written DWARF" # DW_AT_producer
.short 29 # DW_AT_language
.quad 0 # DW_AT_low_pc
.byte 1 # DW_AT_ranges
.long .Lrnglists_table_base0 # DW_AT_rnglists_base
.byte 2 # Abbrev [2] DW_TAG_subprogram
.quad baz # DW_AT_low_pc
.quad .Lbaz_end # DW_AT_high_pc
.asciz "baz" # DW_AT_name
.byte 2 # Abbrev [2] DW_TAG_subprogram
.quad bar # DW_AT_low_pc
.quad .Lbar_end # DW_AT_high_pc
.asciz "bar" # DW_AT_name
.byte 3 # Abbrev [3] DW_TAG_subprogram
.byte 0 # DW_AT_ranges
.byte 1 # DW_AT_frame_base
.byte 86
.asciz "foo" # DW_AT_name
.byte 4 # Abbrev [4] DW_TAG_formal_parameter
.byte 2 # DW_AT_location
.byte 145
.byte 120
.asciz "flag" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.byte 0 # End Of Children Mark
.byte 2 # Abbrev [2] DW_TAG_subprogram
.quad main # DW_AT_low_pc
.quad .Lmain_end # DW_AT_high_pc
.asciz "main" # DW_AT_name
.Lint:
.byte 5 # Abbrev [5] DW_TAG_base_type
.asciz "int" # DW_AT_name
.byte 5 # DW_AT_encoding
.byte 4 # DW_AT_byte_size
.byte 0 # End Of Children Mark
.Ldebug_info_end0:

.section .debug_rnglists,"",@progbits
.long .Ldebug_list_header_end0-.Ldebug_list_header_start0 # Length
.Ldebug_list_header_start0:
.short 5 # Version
.byte 8 # Address size
.byte 0 # Segment selector size
.long 2 # Offset entry count
.Lrnglists_table_base0:
.long .Ldebug_ranges0-.Lrnglists_table_base0
.long .Ldebug_ranges1-.Lrnglists_table_base0
.Ldebug_ranges0:
.byte 6 # DW_RLE_start_end
.quad foo
.quad .Lfoo_end
.byte 6 # DW_RLE_start_end
.quad foo.__part.1
.quad .Lfoo.__part.1_end
.byte 6 # DW_RLE_start_end
.quad foo.__part.2
.quad .Lfoo.__part.2_end
.byte 6 # DW_RLE_start_end
.quad foo.__part.3
.quad .Lfoo.__part.3_end
.byte 0 # DW_RLE_end_of_list
.Ldebug_ranges1:
.byte 6 # DW_RLE_start_end
.quad baz
.quad .Lbaz_end
.byte 6 # DW_RLE_start_end
.quad bar
.quad .Lbar_end
.byte 6 # DW_RLE_start_end
.quad foo.__part.1
.quad .Lfoo.__part.1_end
.byte 6 # DW_RLE_start_end
.quad foo.__part.2
.quad .Lfoo.__part.2_end
.byte 6 # DW_RLE_start_end
.quad foo.__part.3
.quad .Lfoo.__part.3_end
.byte 6 # DW_RLE_start_end
.quad foo
.quad .Lfoo_end
.byte 6 # DW_RLE_start_end
.quad main
.quad .Lmain_end
.byte 0 # DW_RLE_end_of_list
.Ldebug_list_header_end0:

.section ".note.GNU-stack","",@progbits
26 changes: 26 additions & 0 deletions lldb/test/Shell/Unwind/Inputs/linux-x86_64.yaml
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@@ -0,0 +1,26 @@
--- !minidump
Streams:
- Type: ThreadList
Threads:
- Thread Id: 0x000074DD
Context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
Stack:
Start of Memory Range: 0x00007FFFC8D0E000
Content: DEADBEEFBAADF00D
- Type: Exception
Thread ID: 0x000074DD
Exception Record:
Exception Code: 0x0000000B
Thread Context: 00000000
- Type: SystemInfo
Processor Arch: AMD64
Processor Level: 6
Processor Revision: 15876
Number of Processors: 40
Platform ID: Linux
CSD Version: 'Linux 3.13.0-91-generic'
CPU:
Vendor ID: GenuineIntel
Version Info: 0x00000000
Feature Info: 0x00000000
...
65 changes: 65 additions & 0 deletions lldb/test/Shell/Unwind/basic-block-sections-with-dwarf-static.test
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# Test unwind info for functions which have been split into two or more parts.
# In particular, check that the address ranges of these plans are correct, as
# overly large ranges have caused a bug in the past.

# REQUIRES: lld, target-x86_64

# RUN: llvm-mc -triple=x86_64-pc-linux -filetype=obj \
# RUN: %S/Inputs/basic-block-sections-with-dwarf.s > %t.o
# RUN: ld.lld %t.o -o %t
## NB: This minidump exists only as a receptacle for the object file built
## above. This is a workaround for the fact that "image show-unwind" does not
## work without a Process object.
# RUN: yaml2obj %S/Inputs/linux-x86_64.yaml > %t.core
# RUN: %lldb -c %t.core %t -o "image load --file %t --slide 0" -s %s -o exit | \
# RUN: FileCheck --implicit-check-not="UNWIND PLANS" %s

image show-unwind -n foo
# CHECK: UNWIND PLANS for {{.*}}`foo
#
# CHECK: Asynchronous (not restricted to call-sites) UnwindPlan is 'eh_frame CFI'
# CHECK-NEXT: Synchronous (restricted to call-sites) UnwindPlan is 'eh_frame CFI'

# CHECK: Assembly language inspection UnwindPlan:
# CHECK-NEXT: This UnwindPlan originally sourced from assembly insn profiling
# CHECK-NEXT: This UnwindPlan is sourced from the compiler: no.
# CHECK-NEXT: This UnwindPlan is valid at all instruction locations: yes.
# CHECK-NEXT: This UnwindPlan is for a trap handler function: no.
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 6-0x0000000000000019)

# CHECK: eh_frame UnwindPlan:
# CHECK-NEXT: This UnwindPlan originally sourced from eh_frame CFI
# CHECK-NEXT: This UnwindPlan is sourced from the compiler: yes.
# CHECK-NEXT: This UnwindPlan is valid at all instruction locations: no.
# CHECK-NEXT: This UnwindPlan is for a trap handler function: no.
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 6-0x0000000000000019)
# CHECK-NEXT: row[0]: 0: CFA=rsp +8 => rip=[CFA-8]
# CHECK-NEXT: row[1]: 1: CFA=rsp+16 => rbp=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[2]: 4: CFA=rbp+16 => rbp=[CFA-16] rip=[CFA-8]
# CHECK-EMPTY:

image show-unwind -n foo.__part.1
# CHECK: UNWIND PLANS for {{.*}}`foo.__part.1

## As of this writing (Oct 2024), the async unwind plan is "assembly insn
## profiling", which isn't ideal, because this "function" does not follow the
## standard ABI. We end up choosing this plan because the eh_frame unwind plan
## looks like the unwind plan for a regular function without the prologue
## information.
# CHECK: Synchronous (restricted to call-sites) UnwindPlan is 'eh_frame CFI'

# CHECK: Assembly language inspection UnwindPlan:
# CHECK-NEXT: This UnwindPlan originally sourced from assembly insn profiling
# CHECK-NEXT: This UnwindPlan is sourced from the compiler: no.
# CHECK-NEXT: This UnwindPlan is valid at all instruction locations: yes.
# CHECK-NEXT: This UnwindPlan is for a trap handler function: no.
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 25-0x0000000000000023)

# CHECK: eh_frame UnwindPlan:
# CHECK-NEXT: This UnwindPlan originally sourced from eh_frame CFI
# CHECK-NEXT: This UnwindPlan is sourced from the compiler: yes.
# CHECK-NEXT: This UnwindPlan is valid at all instruction locations: no.
# CHECK-NEXT: This UnwindPlan is for a trap handler function: no.
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 25-0x0000000000000023)
# CHECK-NEXT: row[0]: 0: CFA=rbp+16 => rbp=[CFA-16] rip=[CFA-8]
# CHECK-EMPTY:
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