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May 7, 2025
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[lldb] Parse DWARF CFI for discontinuous functions #137006

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[lldb] Parse DWARF CFI for discontinuous functions
labath Apr 23, 2025
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labath Apr 23, 2025
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9 changes: 6 additions & 3 deletions lldb/include/lldb/Symbol/DWARFCallFrameInfo.h
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Expand Up @@ -47,12 +47,15 @@ class DWARFCallFrameInfo {
/// Return an UnwindPlan based on the call frame information encoded in the
/// FDE of this DWARFCallFrameInfo section. The returned plan will be valid
/// (at least) for the given address.
bool GetUnwindPlan(const Address &addr, UnwindPlan &unwind_plan);
std::unique_ptr<UnwindPlan> GetUnwindPlan(const Address &addr);

/// Return an UnwindPlan based on the call frame information encoded in the
/// FDE of this DWARFCallFrameInfo section. The returned plan will be valid
/// (at least) for some address in the given range.
bool GetUnwindPlan(const AddressRange &range, UnwindPlan &unwind_plan);
/// (at least) for some address in the given ranges. If no unwind information
/// is found, nullptr is returned. \a addr represents the entry point of the
/// function. It corresponds to the offset zero in the returned UnwindPlan.
std::unique_ptr<UnwindPlan> GetUnwindPlan(llvm::ArrayRef<AddressRange> ranges,
const Address &addr);

typedef RangeVector<lldb::addr_t, uint32_t> FunctionAddressAndSizeVector;

Expand Down
64 changes: 34 additions & 30 deletions lldb/source/Symbol/DWARFCallFrameInfo.cpp
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Expand Up @@ -151,53 +151,57 @@ DWARFCallFrameInfo::DWARFCallFrameInfo(ObjectFile &objfile,
SectionSP &section_sp, Type type)
: m_objfile(objfile), m_section_sp(section_sp), m_type(type) {}

bool DWARFCallFrameInfo::GetUnwindPlan(const Address &addr,
UnwindPlan &unwind_plan) {
return GetUnwindPlan(AddressRange(addr, 1), unwind_plan);
std::unique_ptr<UnwindPlan>
DWARFCallFrameInfo::GetUnwindPlan(const Address &addr) {
return GetUnwindPlan({AddressRange(addr, 1)}, addr);
}

bool DWARFCallFrameInfo::GetUnwindPlan(const AddressRange &range,
UnwindPlan &unwind_plan) {
std::unique_ptr<UnwindPlan>
DWARFCallFrameInfo::GetUnwindPlan(llvm::ArrayRef<AddressRange> ranges,
const Address &addr) {
FDEEntryMap::Entry fde_entry;
Address addr = range.GetBaseAddress();

// Make sure that the Address we're searching for is the same object file as
// this DWARFCallFrameInfo, we only store File offsets in m_fde_index.
ModuleSP module_sp = addr.GetModule();
if (module_sp.get() == nullptr || module_sp->GetObjectFile() == nullptr ||
module_sp->GetObjectFile() != &m_objfile)
return false;
return nullptr;

std::optional<FDEEntryMap::Entry> entry = GetFirstFDEEntryInRange(range);
if (!entry)
return false;
std::vector<AddressRange> valid_ranges;

std::optional<FDE> fde = ParseFDE(entry->data, addr);
if (!fde)
return false;

unwind_plan.SetSourceName(m_type == EH ? "eh_frame CFI" : "DWARF CFI");
auto result = std::make_unique<UnwindPlan>(GetRegisterKind());
result->SetSourceName(m_type == EH ? "eh_frame CFI" : "DWARF CFI");
// In theory the debug_frame info should be valid at all call sites
// ("asynchronous unwind info" as it is sometimes called) but in practice
// gcc et al all emit call frame info for the prologue and call sites, but
// not for the epilogue or all the other locations during the function
// reliably.
unwind_plan.SetUnwindPlanValidAtAllInstructions(eLazyBoolNo);
unwind_plan.SetSourcedFromCompiler(eLazyBoolYes);
unwind_plan.SetRegisterKind(GetRegisterKind());

unwind_plan.SetPlanValidAddressRanges({fde->range});
unwind_plan.SetUnwindPlanForSignalTrap(fde->for_signal_trap ? eLazyBoolYes
: eLazyBoolNo);
unwind_plan.SetReturnAddressRegister(fde->return_addr_reg_num);
int64_t slide =
fde->range.GetBaseAddress().GetFileAddress() - addr.GetFileAddress();
for (UnwindPlan::Row &row : fde->rows) {
row.SlideOffset(slide);
unwind_plan.AppendRow(std::move(row));
result->SetUnwindPlanValidAtAllInstructions(eLazyBoolNo);
result->SetSourcedFromCompiler(eLazyBoolYes);
result->SetUnwindPlanForSignalTrap(eLazyBoolNo);
for (const AddressRange &range : ranges) {
std::optional<FDEEntryMap::Entry> entry = GetFirstFDEEntryInRange(range);
if (!entry)
continue;
std::optional<FDE> fde = ParseFDE(entry->data, addr);
if (!fde)
continue;
int64_t slide =
fde->range.GetBaseAddress().GetFileAddress() - addr.GetFileAddress();
valid_ranges.push_back(std::move(fde->range));
if (fde->for_signal_trap)
result->SetUnwindPlanForSignalTrap(eLazyBoolYes);
result->SetReturnAddressRegister(fde->return_addr_reg_num);
for (UnwindPlan::Row &row : fde->rows) {
row.SlideOffset(slide);
result->AppendRow(std::move(row));
}
}

return true;
result->SetPlanValidAddressRanges(std::move(valid_ranges));
if (result->GetRowCount() == 0)
return nullptr;
return result;
}

bool DWARFCallFrameInfo::GetAddressRange(Address addr, AddressRange &range) {
Expand Down
21 changes: 7 additions & 14 deletions lldb/source/Symbol/FuncUnwinders.cpp
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Expand Up @@ -149,13 +149,9 @@ FuncUnwinders::GetEHFrameUnwindPlan(Target &target) {
return m_unwind_plan_eh_frame_sp;

m_tried_unwind_plan_eh_frame = true;
if (m_range.GetBaseAddress().IsValid()) {
DWARFCallFrameInfo *eh_frame = m_unwind_table.GetEHFrameInfo();
if (eh_frame) {
auto plan_sp = std::make_shared<UnwindPlan>(lldb::eRegisterKindGeneric);
if (eh_frame->GetUnwindPlan(m_range, *plan_sp))
m_unwind_plan_eh_frame_sp = std::move(plan_sp);
}
if (m_addr.IsValid()) {
if (DWARFCallFrameInfo *eh_frame = m_unwind_table.GetEHFrameInfo())
m_unwind_plan_eh_frame_sp = eh_frame->GetUnwindPlan(m_ranges, m_addr);
}
return m_unwind_plan_eh_frame_sp;
}
Expand All @@ -167,13 +163,10 @@ FuncUnwinders::GetDebugFrameUnwindPlan(Target &target) {
return m_unwind_plan_debug_frame_sp;

m_tried_unwind_plan_debug_frame = true;
if (m_range.GetBaseAddress().IsValid()) {
DWARFCallFrameInfo *debug_frame = m_unwind_table.GetDebugFrameInfo();
if (debug_frame) {
auto plan_sp = std::make_shared<UnwindPlan>(lldb::eRegisterKindGeneric);
if (debug_frame->GetUnwindPlan(m_range, *plan_sp))
m_unwind_plan_debug_frame_sp = std::move(plan_sp);
}
if (!m_ranges.empty()) {
if (DWARFCallFrameInfo *debug_frame = m_unwind_table.GetDebugFrameInfo())
m_unwind_plan_debug_frame_sp =
debug_frame->GetUnwindPlan(m_ranges, m_addr);
}
return m_unwind_plan_debug_frame_sp;
}
Expand Down
27 changes: 15 additions & 12 deletions lldb/source/Symbol/UnwindTable.cpp
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Expand Up @@ -122,6 +122,13 @@ AddressRanges UnwindTable::GetAddressRanges(const Address &addr,
return {};
}

static Address GetFunctionOrSymbolAddress(const Address &addr,
const SymbolContext &sc) {
if (Address result = sc.GetFunctionOrSymbolAddress(); result.IsValid())
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lol at first I was like wait, does that actually work, but sure enough in C++17.

return result;
return addr;
}

FuncUnwindersSP
UnwindTable::GetFuncUnwindersContainingAddress(const Address &addr,
const SymbolContext &sc) {
Expand All @@ -131,25 +138,20 @@ UnwindTable::GetFuncUnwindersContainingAddress(const Address &addr,

// There is an UnwindTable per object file, so we can safely use file handles
addr_t file_addr = addr.GetFileAddress();
iterator end = m_unwinds.end();
iterator insert_pos = end;
if (!m_unwinds.empty()) {
insert_pos = m_unwinds.lower_bound(file_addr);
iterator pos = insert_pos;
if ((pos == m_unwinds.end()) ||
(pos != m_unwinds.begin() &&
pos->second->GetFunctionStartAddress() != addr))
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I realized that checking for the start address is not correct here as we're storing the FuncUnwinders multiple times here -- once per address range.

--pos;

iterator insert_pos = m_unwinds.upper_bound(file_addr);
if (insert_pos != m_unwinds.begin()) {
auto pos = std::prev(insert_pos);
if (pos->second->ContainsAddress(addr))
return pos->second;
}

Address start_addr = GetFunctionOrSymbolAddress(addr, sc);
AddressRanges ranges = GetAddressRanges(addr, sc);
if (ranges.empty())
return nullptr;

auto func_unwinder_sp = std::make_shared<FuncUnwinders>(*this, addr, ranges);
auto func_unwinder_sp =
std::make_shared<FuncUnwinders>(*this, start_addr, ranges);
for (const AddressRange &range : ranges)
m_unwinds.emplace_hint(insert_pos, range.GetBaseAddress().GetFileAddress(),
func_unwinder_sp);
Expand All @@ -164,11 +166,12 @@ FuncUnwindersSP UnwindTable::GetUncachedFuncUnwindersContainingAddress(
const Address &addr, const SymbolContext &sc) {
Initialize();

Address start_addr = GetFunctionOrSymbolAddress(addr, sc);
AddressRanges ranges = GetAddressRanges(addr, sc);
if (ranges.empty())
return nullptr;

return std::make_shared<FuncUnwinders>(*this, addr, std::move(ranges));
return std::make_shared<FuncUnwinders>(*this, start_addr, std::move(ranges));
}

void UnwindTable::Dump(Stream &s) {
Expand Down
20 changes: 9 additions & 11 deletions lldb/source/Target/RegisterContextUnwind.cpp
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Expand Up @@ -868,13 +868,11 @@ RegisterContextUnwind::GetFullUnwindPlanForFrame() {

// Even with -fomit-frame-pointer, we can try eh_frame to get back on
// track.
DWARFCallFrameInfo *eh_frame =
pc_module_sp->GetUnwindTable().GetEHFrameInfo();
if (eh_frame) {
auto unwind_plan_sp =
std::make_shared<UnwindPlan>(lldb::eRegisterKindGeneric);
if (eh_frame->GetUnwindPlan(m_current_pc, *unwind_plan_sp))
return unwind_plan_sp;
if (DWARFCallFrameInfo *eh_frame =
pc_module_sp->GetUnwindTable().GetEHFrameInfo()) {
if (std::unique_ptr<UnwindPlan> plan_up =
eh_frame->GetUnwindPlan(m_current_pc))
return plan_up;
}

ArmUnwindInfo *arm_exidx =
Expand Down Expand Up @@ -1345,9 +1343,9 @@ RegisterContextUnwind::SavedLocationForRegister(
// value instead of the Return Address register.
// If $pc is not available, fall back to the RA reg.
UnwindPlan::Row::AbstractRegisterLocation scratch;
if (m_frame_type == eTrapHandlerFrame &&
active_row->GetRegisterInfo
(pc_regnum.GetAsKind (unwindplan_registerkind), scratch)) {
if (m_frame_type == eTrapHandlerFrame && active_row &&
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This is a splattering of defensive checks as it's easier to get a null active row now (some places around here are already checking it, but not all of them).

active_row->GetRegisterInfo(
pc_regnum.GetAsKind(unwindplan_registerkind), scratch)) {
UnwindLogMsg("Providing pc register instead of rewriting to "
"RA reg because this is a trap handler and there is "
"a location for the saved pc register value.");
Expand Down Expand Up @@ -1377,7 +1375,7 @@ RegisterContextUnwind::SavedLocationForRegister(
}
}

if (regnum.IsValid() &&
if (regnum.IsValid() && active_row &&
active_row->GetRegisterInfo(regnum.GetAsKind(unwindplan_registerkind),
unwindplan_regloc)) {
have_unwindplan_regloc = true;
Expand Down
54 changes: 30 additions & 24 deletions lldb/test/Shell/Unwind/Inputs/basic-block-sections-with-dwarf.s
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Expand Up @@ -4,7 +4,9 @@
# 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.
# The function bar has been placed "in the middle" of foo. The functions are not
# using the frame pointer register and the are deliberately adjusting the stack
# pointer to test that we're using the correct unwind row.

.text

Expand All @@ -20,35 +22,36 @@ baz:
.type foo,@function
foo:
.cfi_startproc
pushq %rbp
pushq %rbx
.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)
.cfi_offset %rbx, -16
movl %edi, %ebx
cmpl $0, %ebx
je foo.__part.2
jmp foo.__part.1
.cfi_endproc
.Lfoo_end:
.size foo, .Lfoo_end-foo

# NB: Deliberately inserting padding to separate the two parts of the function
# as we're currently only parsing a single FDE entry from a (coalesced) address
# range.
nop

foo.__part.1:
.cfi_startproc
.cfi_def_cfa %rbp, 16
.cfi_offset %rbp, -16
.cfi_def_cfa_offset 16
.cfi_offset %rbx, -16
subq $16, %rsp
.cfi_def_cfa_offset 32
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
Expand All @@ -62,22 +65,26 @@ bar:

foo.__part.2:
.cfi_startproc
.cfi_def_cfa %rbp, 16
.cfi_offset %rbp, -16
.cfi_def_cfa_offset 16
.cfi_offset %rbx, -16
subq $16, %rsp
.cfi_def_cfa_offset 32
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

# NB: Deliberately inserting padding to separate the two parts of the function
# as we're currently only parsing a single FDE entry from a (coalesced) address
# range.
nop

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_offset 32
.cfi_offset %rbx, -16
addq $24, %rsp
.cfi_def_cfa %rsp, 8
retq
.Lfoo.__part.3_end:
Expand Down Expand Up @@ -186,9 +193,8 @@ main:
.byte 86
.asciz "foo" # DW_AT_name
.byte 4 # Abbrev [4] DW_TAG_formal_parameter
.byte 2 # DW_AT_location
.byte 145
.byte 120
.byte 1 # DW_AT_location
.byte 0x53 # DW_OP_reg3
.asciz "flag" # DW_AT_name
.long .Lint-.Lcu_begin0 # DW_AT_type
.byte 0 # End Of Children Mark
Expand Down
37 changes: 23 additions & 14 deletions lldb/test/Shell/Unwind/basic-block-sections-with-dwarf-static.test
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Expand Up @@ -17,23 +17,32 @@
image show-unwind --cached true -n foo
# CHECK: UNWIND PLANS for {{.*}}`foo
#
# 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: 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.
# TODO: This address range isn't correct right now. We're just checking that
# it's a different range from the one in the next query.
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 6-0x0000000000000046)
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 6-0x0000000000000010)[{{.*}}.text + 17-0x000000000000001c)[{{.*}}.text + 44-0x0000000000000037)[{{.*}}.text + 56-0x000000000000003d)
# CHECK-NEXT: row[0]: 0: CFA=rsp +8 => rip=[CFA-8]
# CHECK-NEXT: row[1]: 1: CFA=rsp+16 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[2]: 11: CFA=rsp+16 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[3]: 15: CFA=rsp+32 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[4]: 38: CFA=rsp+16 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[5]: 42: CFA=rsp+32 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[6]: 50: CFA=rsp+32 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-NEXT: row[7]: 54: CFA=rsp +8 => rbx=[CFA-16] rip=[CFA-8]
# CHECK-EMPTY:

image show-unwind --cached true -n bar
# CHECK: UNWIND PLANS for {{.*}}`bar

# 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: 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.
# TODO: This address range isn't correct right now. We're just checking that
# it's a different range from the one in the previous query.
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 35-0x0000000000000033)
# CHECK-NEXT: Address range of this UnwindPlan: [{{.*}}.text + 28-0x000000000000002c)
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obviously not relevant to this PR but man Address range of this UnwindPlan: [{{.*}}.text + 28-0x000000000000002c is ugly. I wonder if AddressRange::Dump should call DumpAddress(s->AsRawOstream(), m_base_addr.GetOffset() + GetByteSize(), 1); (1 instead of addr_size as it does today) for DumpStyleSectionNameOffset - so it's not address-size zero padded - but I'm sure that would break some other tabular printing elsewhere, so nevermind.

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Yeah, it's quite a mess. I've been planning to look into that.

# CHECK-NEXT: row[0]: 0: CFA=rsp +8 => rip=[CFA-8]
# CHECK-NEXT: row[1]: 4: CFA=rsp+32 => rip=[CFA-8]
# CHECK-NEXT: row[2]: 15: CFA=rsp +8 => rip=[CFA-8]
# CHECK-EMPTY:
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