[Lldb-commits] [lldb] 5d088ba - [lldb] Track CFA pointer metadata in StackID (#157498)
via lldb-commits
lldb-commits at lists.llvm.org
Fri Sep 12 09:17:52 PDT 2025
Author: Felipe de Azevedo Piovezan
Date: 2025-09-12T09:17:48-07:00
New Revision: 5d088ba30440d37f180f6b2e2f2fcc25d5c77018
URL: https://github.com/llvm/llvm-project/commit/5d088ba30440d37f180f6b2e2f2fcc25d5c77018
DIFF: https://github.com/llvm/llvm-project/commit/5d088ba30440d37f180f6b2e2f2fcc25d5c77018.diff
LOG: [lldb] Track CFA pointer metadata in StackID (#157498)
[lldb] Track CFA pointer metadata in StackID
In this commit:
9c8e71644227 [lldb] Make StackID call Fix{Code,Data} pointers (#152796)
We made StackID keep track of the CFA without any pointer metadata in
it. This is necessary when comparing two StackIDs to determine which one
is "younger".
However, the CFA inside StackIDs is also used in other contexts through
the method StackID::GetCallFrameAddress. One notable case is
DWARFExpression: the computation of `DW_OP_call_frame_address` is done
using StackID. This feeds into many other places, e.g. expression
evaluation may require the address of a variable that is computed from
the CFA; to access the variable without faulting, we may need to
preserve the pointer metadata. As such, StackID must be able to provide
both versions of the CFA.
In the spirit of allowing consumers of pointers to decide what to do
with pointer metadata, this patch changes StackID to store both versions
of the cfa pointer. Two getter methods are provided, and all call sites
except DWARFExpression preserve their existing behavior (stripped
pointer). Other alternatives were considered:
* Just store the raw pointer. This would require changing the
comparisong operator `<` to also receive a Process, as the comparison
requires stripped pointers. It wasn't clear if all call-sites had a
non-null process, whereas we know we have a process when creating a
StackID.
* Store a weak pointer to the process inside the class, and then strip
metadata as needed. This would require a `weak_ptr::lock` in many
operations of LLDB, and it felt wasteful. It also prevents stripping
of the pointer if the process has gone away.
This patch also changes RegisterContextUnwind::ReadFrameAddress, which
is the method computing the CFA fed into StackID, to also preserve the
signature pointers.
Added:
lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/Makefile
lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/TestArmPointerMetadataCFADwarfExpr.py
lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/main.s
Modified:
lldb/include/lldb/Target/StackID.h
lldb/source/API/SBFrame.cpp
lldb/source/Expression/DWARFExpression.cpp
lldb/source/Target/RegisterContextUnwind.cpp
lldb/source/Target/StackFrameList.cpp
lldb/source/Target/StackID.cpp
Removed:
################################################################################
diff --git a/lldb/include/lldb/Target/StackID.h b/lldb/include/lldb/Target/StackID.h
index c2a5d733dcd69..18461533d648a 100644
--- a/lldb/include/lldb/Target/StackID.h
+++ b/lldb/include/lldb/Target/StackID.h
@@ -26,7 +26,11 @@ class StackID {
lldb::addr_t GetPC() const { return m_pc; }
- lldb::addr_t GetCallFrameAddress() const { return m_cfa; }
+ lldb::addr_t GetCallFrameAddressWithMetadata() const {
+ return m_cfa_with_metadata;
+ }
+
+ lldb::addr_t GetCallFrameAddressWithoutMetadata() const { return m_cfa; }
SymbolContextScope *GetSymbolContextScope() const { return m_symbol_scope; }
@@ -62,6 +66,9 @@ class StackID {
/// below)
lldb::addr_t m_cfa = LLDB_INVALID_ADDRESS;
+ /// The cfa with metadata (i.e. prior to Process::FixAddress).
+ lldb::addr_t m_cfa_with_metadata = LLDB_INVALID_ADDRESS;
+
/// If nullptr, there is no block or symbol for this frame. If not nullptr,
/// this will either be the scope for the lexical block for the frame, or the
/// scope for the symbol. Symbol context scopes are always be unique pointers
diff --git a/lldb/source/API/SBFrame.cpp b/lldb/source/API/SBFrame.cpp
index b6724bb0c4119..42dbed490a33d 100644
--- a/lldb/source/API/SBFrame.cpp
+++ b/lldb/source/API/SBFrame.cpp
@@ -267,7 +267,7 @@ lldb::addr_t SBFrame::GetCFA() const {
}
if (StackFrame *frame = exe_ctx->GetFramePtr())
- return frame->GetStackID().GetCallFrameAddress();
+ return frame->GetStackID().GetCallFrameAddressWithoutMetadata();
return LLDB_INVALID_ADDRESS;
}
diff --git a/lldb/source/Expression/DWARFExpression.cpp b/lldb/source/Expression/DWARFExpression.cpp
index 332cf2c86024a..5040351f4975b 100644
--- a/lldb/source/Expression/DWARFExpression.cpp
+++ b/lldb/source/Expression/DWARFExpression.cpp
@@ -2195,7 +2195,7 @@ llvm::Expected<Value> DWARFExpression::Evaluate(
// Note that we don't have to parse FDEs because this DWARF expression
// is commonly evaluated with a valid stack frame.
StackID id = frame->GetStackID();
- addr_t cfa = id.GetCallFrameAddress();
+ addr_t cfa = id.GetCallFrameAddressWithMetadata();
if (cfa != LLDB_INVALID_ADDRESS) {
stack.push_back(Scalar(cfa));
stack.back().SetValueType(Value::ValueType::LoadAddress);
diff --git a/lldb/source/Target/RegisterContextUnwind.cpp b/lldb/source/Target/RegisterContextUnwind.cpp
index 787eb94be3b48..3b018c09b8b72 100644
--- a/lldb/source/Target/RegisterContextUnwind.cpp
+++ b/lldb/source/Target/RegisterContextUnwind.cpp
@@ -2039,8 +2039,6 @@ bool RegisterContextUnwind::ReadFrameAddress(
reg_info, cfa_reg_contents, reg_info->byte_size, reg_value);
if (error.Success()) {
address = reg_value.GetAsUInt64();
- if (abi_sp)
- address = abi_sp->FixCodeAddress(address);
UnwindLogMsg(
"CFA value via dereferencing reg %s (%d): reg has val 0x%" PRIx64
", CFA value is 0x%" PRIx64,
@@ -2062,8 +2060,6 @@ bool RegisterContextUnwind::ReadFrameAddress(
RegisterNumber cfa_reg(m_thread, row_register_kind,
fa.GetRegisterNumber());
if (ReadGPRValue(cfa_reg, cfa_reg_contents)) {
- if (abi_sp)
- cfa_reg_contents = abi_sp->FixDataAddress(cfa_reg_contents);
if (cfa_reg_contents == LLDB_INVALID_ADDRESS || cfa_reg_contents == 0 ||
cfa_reg_contents == 1) {
UnwindLogMsg(
@@ -2100,9 +2096,6 @@ bool RegisterContextUnwind::ReadFrameAddress(
dwarfexpr.Evaluate(&exe_ctx, this, 0, nullptr, nullptr);
if (result) {
address = result->GetScalar().ULongLong();
- if (ABISP abi_sp = m_thread.GetProcess()->GetABI())
- address = abi_sp->FixCodeAddress(address);
-
UnwindLogMsg("CFA value set by DWARF expression is 0x%" PRIx64,
address);
return true;
@@ -2143,7 +2136,6 @@ bool RegisterContextUnwind::ReadFrameAddress(
}
case UnwindPlan::Row::FAValue::isConstant: {
address = fa.GetConstant();
- address = m_thread.GetProcess()->FixDataAddress(address);
UnwindLogMsg("CFA value set by constant is 0x%" PRIx64, address);
return true;
}
diff --git a/lldb/source/Target/StackFrameList.cpp b/lldb/source/Target/StackFrameList.cpp
index fa5d159c0c91a..ccf874fc03ebd 100644
--- a/lldb/source/Target/StackFrameList.cpp
+++ b/lldb/source/Target/StackFrameList.cpp
@@ -449,7 +449,7 @@ bool StackFrameList::FetchFramesUpTo(uint32_t end_idx,
}
} else {
unwind_frame_sp = m_frames.front();
- cfa = unwind_frame_sp->m_id.GetCallFrameAddress();
+ cfa = unwind_frame_sp->m_id.GetCallFrameAddressWithoutMetadata();
}
} else {
// Check for interruption when building the frames.
diff --git a/lldb/source/Target/StackID.cpp b/lldb/source/Target/StackID.cpp
index f879276527dda..137c776a84d2f 100644
--- a/lldb/source/Target/StackID.cpp
+++ b/lldb/source/Target/StackID.cpp
@@ -17,7 +17,8 @@ using namespace lldb_private;
StackID::StackID(lldb::addr_t pc, lldb::addr_t cfa,
SymbolContextScope *symbol_scope, Process *process)
- : m_pc(pc), m_cfa(cfa), m_symbol_scope(symbol_scope) {
+ : m_pc(pc), m_cfa(cfa), m_cfa_with_metadata(cfa),
+ m_symbol_scope(symbol_scope) {
if (process) {
m_pc = process->FixCodeAddress(m_pc);
m_cfa = process->FixDataAddress(m_cfa);
@@ -29,6 +30,7 @@ void StackID::SetPC(lldb::addr_t pc, Process *process) {
}
void StackID::SetCFA(lldb::addr_t cfa, Process *process) {
+ m_cfa_with_metadata = cfa;
m_cfa = process ? process->FixDataAddress(cfa) : cfa;
}
@@ -49,7 +51,8 @@ void StackID::Dump(Stream *s) {
}
bool lldb_private::operator==(const StackID &lhs, const StackID &rhs) {
- if (lhs.GetCallFrameAddress() != rhs.GetCallFrameAddress())
+ if (lhs.GetCallFrameAddressWithoutMetadata() !=
+ rhs.GetCallFrameAddressWithoutMetadata())
return false;
SymbolContextScope *lhs_scope = lhs.GetSymbolContextScope();
@@ -67,8 +70,8 @@ bool lldb_private::operator!=(const StackID &lhs, const StackID &rhs) {
}
bool lldb_private::operator<(const StackID &lhs, const StackID &rhs) {
- const lldb::addr_t lhs_cfa = lhs.GetCallFrameAddress();
- const lldb::addr_t rhs_cfa = rhs.GetCallFrameAddress();
+ const lldb::addr_t lhs_cfa = lhs.GetCallFrameAddressWithoutMetadata();
+ const lldb::addr_t rhs_cfa = rhs.GetCallFrameAddressWithoutMetadata();
// FIXME: We are assuming that the stacks grow downward in memory. That's not
// necessary, but true on
diff --git a/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/Makefile b/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/Makefile
new file mode 100644
index 0000000000000..f0de8ffca59fc
--- /dev/null
+++ b/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/Makefile
@@ -0,0 +1,11 @@
+ASM_SOURCES := main.s
+
+# This is to appease Makefile.rules, there is no main.c
+C_SOURCES := main.c
+
+ASM_OBJS := $(ASM_SOURCES:.s=.o)
+
+%.o: %.s
+ $(CC) -c -x assembler $< -o $@
+
+include Makefile.rules
diff --git a/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/TestArmPointerMetadataCFADwarfExpr.py b/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/TestArmPointerMetadataCFADwarfExpr.py
new file mode 100644
index 0000000000000..839e0e1a4fc4d
--- /dev/null
+++ b/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/TestArmPointerMetadataCFADwarfExpr.py
@@ -0,0 +1,35 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+ at skipUnlessDarwin
+ at skipIf(archs=no_match(["arm64"]))
+class TestArmPointerMetadataStripping(TestBase):
+ def test(self):
+ self.build()
+ target, process, thread, bkpt = lldbutil.run_to_name_breakpoint(self, "foo")
+
+ # Step over the first two instructions of foo in order to
+ # toggle the bit of fp and save it on the stack:
+ # orr x29, x29, #0x1000000000000000
+ # stp x29, x30, [sp, #-16]!
+ # This is effectively adding metadata to the CFA of the caller frame (main).
+ thread.StepInstruction(False)
+ thread.StepInstruction(False)
+
+ # The location of `argv` has been artificially made equal to the CFA of the frame.
+ # As such, it should have the metadata artificially set previously.
+ argv_addr = thread.frames[1].GetValueForVariablePath("&argv")
+ self.assertTrue(argv_addr.IsValid())
+ argv_addr_uint = argv_addr.GetValueAsUnsigned()
+ self.assertNotEqual((argv_addr_uint & (1 << 60)), 0)
+
+ # GetCFA strips metadata.
+ cfa = thread.frames[1].GetCFA()
+ self.assertEqual((cfa & (1 << 60)), 0)
+
+ # If the test worked correctly, the cfa and the location should be identical,
+ # modulo the metadata.
+ self.assertEqual(cfa | (1 << 60), argv_addr_uint)
diff --git a/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/main.s b/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/main.s
new file mode 100644
index 0000000000000..0825c5ddd08b5
--- /dev/null
+++ b/lldb/test/API/macosx/arm-pointer-metadata-cfa-dwarf-expr/main.s
@@ -0,0 +1,226 @@
+; The assembly below corresponds to this program:
+; __attribute__((nodebug))
+; int foo() {
+; return 10;
+; }
+; int main(int argc, char **argv) {
+; foo();
+; return 0;
+; }
+;
+; The assembly was edited in two places (search for "EDIT"):
+; 1. A "orr x29, x29, #0x1000000000000000" instruction was added in foo. This
+; effectively changes the CFA value of the frame above foo (i.e. main).
+; 2. In main, the DWARF location of `argv` was changed to DW_AT_call_frame_cfa.
+;
+; This allows us to stop in foo, go to frame 1 (main) and do `v &argv`,
+; obtaining the result of evaluating DW_AT_call_frame_cfa.
+
+ .section __TEXT,__text,regular,pure_instructions
+ .globl _foo ; -- Begin function foo
+ .p2align 2
+_foo: ; @foo
+Lfunc_begin0:
+ .cfi_startproc
+ orr x29, x29, #0x1000000000000000 ; EDIT: Set top byte of fp.
+ stp x29, x30, [sp, #-16]! ; 16-byte Folded Spill
+ mov x29, sp
+ .cfi_def_cfa w29, 16
+ .cfi_offset w30, -8
+ .cfi_offset w29, -16
+ mov w0, #10 ; =0xa
+ ldp x29, x30, [sp], #16 ; 16-byte Folded Reload
+ ret
+Lfunc_end0:
+ .cfi_endproc
+ ; -- End function
+ .globl _main ; -- Begin function main
+ .p2align 2
+_main: ; @main
+Lfunc_begin1:
+ .file 1 "/test" "test.c"
+ .loc 1 6 0 ; test.c:6:0
+ .cfi_startproc
+ sub sp, sp, #48
+ stp x29, x30, [sp, #32] ; 16-byte Folded Spill
+ add x29, sp, #32
+ .cfi_def_cfa w29, 16
+ .cfi_offset w30, -8
+ .cfi_offset w29, -16
+ mov w8, #0 ; =0x0
+ str w8, [sp, #12] ; 4-byte Folded Spill
+ stur wzr, [x29, #-4]
+ stur w0, [x29, #-8]
+ str x1, [sp, #16]
+Ltmp0:
+ bl _foo
+ ldr w0, [sp, #12] ; 4-byte Folded Reload
+ ldp x29, x30, [sp, #32] ; 16-byte Folded Reload
+ add sp, sp, #48
+ ret
+Ltmp1:
+Lfunc_end1:
+ .cfi_endproc
+ ; -- End function
+ .section __DWARF,__debug_abbrev,regular,debug
+Lsection_abbrev:
+ .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 3 ; DW_AT_name
+ .byte 14 ; DW_FORM_strp
+ .ascii "\202|" ; DW_AT_LLVM_sysroot
+ .byte 14 ; DW_FORM_strp
+ .ascii "\357\177" ; DW_AT_APPLE_sdk
+ .byte 14 ; DW_FORM_strp
+ .byte 16 ; DW_AT_stmt_list
+ .byte 23 ; DW_FORM_sec_offset
+ .byte 27 ; DW_AT_comp_dir
+ .byte 14 ; DW_FORM_strp
+ .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 64 ; DW_AT_frame_base
+ .byte 24 ; DW_FORM_exprloc
+ .byte 3 ; DW_AT_name
+ .byte 14 ; DW_FORM_strp
+ .byte 58 ; DW_AT_decl_file
+ .byte 11 ; DW_FORM_data1
+ .byte 59 ; DW_AT_decl_line
+ .byte 11 ; DW_FORM_data1
+ .byte 39 ; DW_AT_prototyped
+ .byte 25 ; DW_FORM_flag_present
+ .byte 73 ; DW_AT_type
+ .byte 19 ; DW_FORM_ref4
+ .byte 63 ; DW_AT_external
+ .byte 25 ; DW_FORM_flag_present
+ .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 24 ; DW_FORM_exprloc
+ .byte 3 ; DW_AT_name
+ .byte 14 ; DW_FORM_strp
+ .byte 58 ; DW_AT_decl_file
+ .byte 11 ; DW_FORM_data1
+ .byte 59 ; DW_AT_decl_line
+ .byte 11 ; DW_FORM_data1
+ .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 5 ; Abbreviation Code
+ .byte 15 ; DW_TAG_pointer_type
+ .byte 0 ; DW_CHILDREN_no
+ .byte 73 ; DW_AT_type
+ .byte 19 ; DW_FORM_ref4
+ .byte 0 ; EOM(1)
+ .byte 0 ; EOM(2)
+ .byte 0 ; EOM(3)
+ .section __DWARF,__debug_info,regular,debug
+Lsection_info:
+Lcu_begin0:
+.set Lset0, Ldebug_info_end0-Ldebug_info_start0 ; Length of Unit
+ .long Lset0
+Ldebug_info_start0:
+ .short 4 ; DWARF version number
+.set Lset1, Lsection_abbrev-Lsection_abbrev ; Offset Into Abbrev. Section
+ .long Lset1
+ .byte 8 ; Address Size (in bytes)
+ .byte 1 ; Abbrev [1] 0xb:0x76 DW_TAG_compile_unit
+ .long 0 ; DW_AT_producer
+ .short 12 ; DW_AT_language
+ .long 47 ; DW_AT_name
+ .long 54 ; DW_AT_LLVM_sysroot
+ .long 165 ; DW_AT_APPLE_sdk
+.set Lset2, Lline_table_start0-Lsection_line ; DW_AT_stmt_list
+ .long Lset2
+ .long 180 ; DW_AT_comp_dir
+ .quad Lfunc_begin1 ; DW_AT_low_pc
+.set Lset3, Lfunc_end1-Lfunc_begin1 ; DW_AT_high_pc
+ .long Lset3
+ .byte 2 ; Abbrev [2] 0x32:0x36 DW_TAG_subprogram
+ .quad Lfunc_begin1 ; DW_AT_low_pc
+.set Lset4, Lfunc_end1-Lfunc_begin1 ; DW_AT_high_pc
+ .long Lset4
+ .byte 1 ; DW_AT_frame_base
+ .byte 109
+ .long 247 ; DW_AT_name
+ .byte 1 ; DW_AT_decl_file
+ .byte 6 ; DW_AT_decl_line
+ ; DW_AT_prototyped
+ .long 107 ; DW_AT_type
+ ; DW_AT_external
+ .byte 3 ; Abbrev [3] 0x4b:0xe DW_TAG_formal_parameter
+ .byte 2 ; DW_AT_location
+ .byte 145
+ .byte 120
+ .long 256 ; DW_AT_name
+ .byte 1 ; DW_AT_decl_file
+ .byte 6 ; DW_AT_decl_line
+ .long 103 ; DW_AT_type
+ .byte 3 ; Abbrev [3] 0x59:0xe DW_TAG_formal_parameter
+ .byte 1 ; DW_AT_location
+ .byte 0x9c ; EDIT: DW_AT_call_frame_cfa
+ .long 261 ; DW_AT_name
+ .byte 1 ; DW_AT_decl_file
+ .byte 6 ; DW_AT_decl_line
+ .long 110 ; DW_AT_type
+ .byte 0 ; End Of Children Mark
+ .byte 4 ; Abbrev [4] 0x68:0x7 DW_TAG_base_type
+ .long 252 ; DW_AT_name
+ .byte 5 ; DW_AT_encoding
+ .byte 4 ; DW_AT_byte_size
+ .byte 5 ; Abbrev [5] 0x6f:0x5 DW_TAG_pointer_type
+ .long 115 ; DW_AT_type
+ .byte 5 ; Abbrev [5] 0x74:0x5 DW_TAG_pointer_type
+ .long 120 ; DW_AT_type
+ .byte 4 ; Abbrev [4] 0x79:0x7 DW_TAG_base_type
+ .long 266 ; DW_AT_name
+ .byte 6 ; DW_AT_encoding
+ .byte 1 ; DW_AT_byte_size
+ .byte 0 ; End Of Children Mark
+Ldebug_info_end0:
+ .section __DWARF,__debug_str,regular,debug
+Linfo_string:
+ .asciz "Apple clang " ; string offset=0
+ .asciz "test.c" ; string offset=47
+ .asciz "/Applications/Xcode..........................................................................................." ; string offset=54
+ .asciz ".............." ; string offset=165
+ .asciz "......................................................../llvm_src1" ; string offset=180
+ .asciz "main" ; string offset=247
+ .asciz "int" ; string offset=252
+ .asciz "argc" ; string offset=256
+ .asciz "argv" ; string offset=261
+ .asciz "char" ; string offset=266
+.subsections_via_symbols
+ .section __DWARF,__debug_line,regular,debug
+Lsection_line:
+Lline_table_start0:
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