necipfazil updated this revision to Diff 361091.
necipfazil marked 10 inline comments as done.
necipfazil added a comment.
Fix nits in documentation and tests
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D105907/new/
https://reviews.llvm.org/D105907
Files:
clang/docs/CallGraphSection.rst
clang/include/clang/Basic/CodeGenOptions.def
clang/include/clang/Driver/Options.td
clang/lib/CodeGen/BackendUtil.cpp
clang/lib/Driver/ToolChains/Clang.cpp
clang/test/Driver/call-graph-section.c
llvm/include/llvm/CodeGen/CommandFlags.h
llvm/include/llvm/Target/TargetOptions.h
llvm/lib/CodeGen/CommandFlags.cpp
Index: llvm/lib/CodeGen/CommandFlags.cpp
===================================================================
--- llvm/lib/CodeGen/CommandFlags.cpp
+++ llvm/lib/CodeGen/CommandFlags.cpp
@@ -86,6 +86,7 @@
CGOPT(DebuggerKind, DebuggerTuningOpt)
CGOPT(bool, EnableStackSizeSection)
CGOPT(bool, EnableAddrsig)
+CGOPT(bool, EnableCallGraphSection)
CGOPT(bool, EmitCallSiteInfo)
CGOPT(bool, EnableMachineFunctionSplitter)
CGOPT(bool, EnableDebugEntryValues)
@@ -407,6 +408,11 @@
cl::init(false));
CGBINDOPT(EnableAddrsig);
+ static cl::opt<bool> EnableCallGraphSection(
+ "call-graph-section", cl::desc("Emit a call graph section"),
+ cl::init(false));
+ CGBINDOPT(EnableCallGraphSection);
+
static cl::opt<bool> EmitCallSiteInfo(
"emit-call-site-info",
cl::desc(
@@ -520,6 +526,7 @@
Options.EmitStackSizeSection = getEnableStackSizeSection();
Options.EnableMachineFunctionSplitter = getEnableMachineFunctionSplitter();
Options.EmitAddrsig = getEnableAddrsig();
+ Options.EmitCallGraphSection = getEnableCallGraphSection();
Options.EmitCallSiteInfo = getEmitCallSiteInfo();
Options.EnableDebugEntryValues = getEnableDebugEntryValues();
Options.PseudoProbeForProfiling = getPseudoProbeForProfiling();
Index: llvm/include/llvm/Target/TargetOptions.h
===================================================================
--- llvm/include/llvm/Target/TargetOptions.h
+++ llvm/include/llvm/Target/TargetOptions.h
@@ -127,11 +127,11 @@
EmulatedTLS(false), ExplicitEmulatedTLS(false), EnableIPRA(false),
EmitStackSizeSection(false), EnableMachineOutliner(false),
EnableMachineFunctionSplitter(false), SupportsDefaultOutlining(false),
- EmitAddrsig(false), EmitCallSiteInfo(false),
- SupportsDebugEntryValues(false), EnableDebugEntryValues(false),
- PseudoProbeForProfiling(false), ValueTrackingVariableLocations(false),
- ForceDwarfFrameSection(false), XRayOmitFunctionIndex(false),
- DebugStrictDwarf(false),
+ EmitAddrsig(false), EmitCallGraphSection(false),
+ EmitCallSiteInfo(false), SupportsDebugEntryValues(false),
+ EnableDebugEntryValues(false), PseudoProbeForProfiling(false),
+ ValueTrackingVariableLocations(false), ForceDwarfFrameSection(false),
+ XRayOmitFunctionIndex(false), DebugStrictDwarf(false),
FPDenormalMode(DenormalMode::IEEE, DenormalMode::IEEE) {}
/// DisableFramePointerElim - This returns true if frame pointer elimination
@@ -290,6 +290,9 @@
/// to selectively generate basic block sections.
std::shared_ptr<MemoryBuffer> BBSectionsFuncListBuf;
+ /// Emit section containing call graph metadata.
+ unsigned EmitCallGraphSection : 1;
+
/// The flag enables call site info production. It is used only for debug
/// info, and it is restricted only to optimized code. This can be used for
/// something else, so that should be controlled in the frontend.
Index: llvm/include/llvm/CodeGen/CommandFlags.h
===================================================================
--- llvm/include/llvm/CodeGen/CommandFlags.h
+++ llvm/include/llvm/CodeGen/CommandFlags.h
@@ -122,6 +122,8 @@
bool getEnableAddrsig();
+bool getEnableCallGraphSection();
+
bool getEmitCallSiteInfo();
bool getEnableMachineFunctionSplitter();
Index: clang/test/Driver/call-graph-section.c
===================================================================
--- /dev/null
+++ clang/test/Driver/call-graph-section.c
@@ -0,0 +1,5 @@
+// RUN: %clang -### -S -fcall-graph-section %s 2>&1 | FileCheck --check-prefix=CALL-GRAPH-SECTION %s
+// RUN: %clang -### -S -fcall-graph-section -fno-call-graph-section %s 2>&1 | FileCheck --check-prefix=NO-CALL-GRAPH-SECTION %s
+
+// CALL-GRAPH-SECTION: "-fcall-graph-section"
+// NO-CALL-GRAPH-SECTION-NOT: "-fcall-graph-section"
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -5576,6 +5576,10 @@
CmdArgs.push_back(A->getValue());
}
+ if (Args.hasFlag(options::OPT_fcall_graph_section,
+ options::OPT_fno_call_graph_section, false))
+ CmdArgs.push_back("-fcall-graph-section");
+
if (Args.hasFlag(options::OPT_fstack_size_section,
options::OPT_fno_stack_size_section, RawTriple.isPS4()))
CmdArgs.push_back("-fstack-size-section");
Index: clang/lib/CodeGen/BackendUtil.cpp
===================================================================
--- clang/lib/CodeGen/BackendUtil.cpp
+++ clang/lib/CodeGen/BackendUtil.cpp
@@ -569,6 +569,7 @@
Options.StackUsageOutput = CodeGenOpts.StackUsageOutput;
Options.EmitAddrsig = CodeGenOpts.Addrsig;
Options.ForceDwarfFrameSection = CodeGenOpts.ForceDwarfFrameSection;
+ Options.EmitCallGraphSection = CodeGenOpts.CallGraphSection;
Options.EmitCallSiteInfo = CodeGenOpts.EmitCallSiteInfo;
Options.EnableAIXExtendedAltivecABI = CodeGenOpts.EnableAIXExtendedAltivecABI;
Options.PseudoProbeForProfiling = CodeGenOpts.PseudoProbeForProfiling;
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -2753,6 +2753,10 @@
defm data_sections : BoolFOption<"data-sections",
CodeGenOpts<"DataSections">, DefaultFalse,
PosFlag<SetTrue, [CC1Option], "Place each data in its own section">, NegFlag<SetFalse>>;
+defm call_graph_section : BoolFOption<"call-graph-section",
+ CodeGenOpts<"CallGraphSection">, DefaultFalse,
+ PosFlag<SetTrue, [CC1Option], "Emit a call graph section">,
+ NegFlag<SetFalse>>;
defm stack_size_section : BoolFOption<"stack-size-section",
CodeGenOpts<"StackSizeSection">, DefaultFalse,
PosFlag<SetTrue, [CC1Option], "Emit section containing metadata on function stack sizes">,
Index: clang/include/clang/Basic/CodeGenOptions.def
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.def
+++ clang/include/clang/Basic/CodeGenOptions.def
@@ -68,6 +68,8 @@
CODEGENOPT(DebugPassManager, 1, 0) ///< Prints debug information for the new
///< pass manager.
CODEGENOPT(DisableRedZone , 1, 0) ///< Set when -mno-red-zone is enabled.
+CODEGENOPT(CallGraphSection, 1, 0) ///< Emit a call graph section into the
+ ///< object file.
CODEGENOPT(EmitCallSiteInfo, 1, 0) ///< Emit call site info only in the case of
///< '-g' + 'O>0' level.
CODEGENOPT(EnableDIPreservationVerify, 1, 0) ///< Enable di preservation verify
Index: clang/docs/CallGraphSection.rst
===================================================================
--- /dev/null
+++ clang/docs/CallGraphSection.rst
@@ -0,0 +1,251 @@
+==================
+Call Graph Section
+==================
+
+Introduction
+============
+
+With ``-fcall-graph-section``, the compiler will create a call graph section
+in the object file. It will include type identifiers for indirect calls and
+targets. This information can be used to map indirect calls to their receivers
+with matching types. A complete and high-precision call graph can be
+reconstructed by complementing this information with disassembly
+(see ``llvm-objdump --call-graph-info``).
+
+Semantics
+=========
+
+A coarse-grained, type-agnostic call graph may allow indirect calls to target
+any function in the program. This approach ensures completeness since no
+indirect call edge is missing. However, it is generally poor in precision
+due to having unneeded edges.
+
+A call graph section provides type identifiers for indirect calls and targets.
+This information can be used to restrict the receivers of an indirect target to
+indirect calls with matching type. Consequently, the precision for indirect
+call edges are improved while maintaining the completeness.
+
+The ``llvm-objdump`` utility provides a ``--call-graph-info`` option to extract
+full call graph information by parsing the content of the call graph section
+and disassembling the program for complementary information, e.g., direct
+calls.
+
+Section layout
+==============
+
+A call graph section consists of zero or more call graph entries.
+Each entry contains information on a function and its indirect calls.
+
+An entry of a call graph section has the following layout in the binary:
+
++---------------------+-----------------------------------------------------------------------+
+| Element | Content |
++=====================+=======================================================================+
+| FormatVersionNumber | Format version number. |
++---------------------+-----------------------------------------------------------------------+
+| FunctionEntryPc | Function entry address. |
++---------------------+-----------------------------------+-----------------------------------+
+| | A flag whether the function is an | - 0: not an indirect target |
+| FunctionKind | indirect target, and if so, | - 1: indirect target, unknown id |
+| | whether its type id is known. | - 2: indirect target, known id |
++---------------------+-----------------------------------+-----------------------------------+
+| FunctionTypeId | Type id for the indirect target. Present only when FunctionKind is 2. |
++---------------------+-----------------------------------------------------------------------+
+| CallSiteCount | Number of type id to indirect call site mappings that follow. |
++---------------------+-----------------------------------------------------------------------+
+| CallSiteList | List of type id and indirect call site pc pairs. |
++---------------------+-----------------------------------------------------------------------+
+
+Each element in an entry (including each element of the contained lists and
+pairs) occupies 64-bit space.
+
+The format version number is repeated per entry to support concatenation of
+call graph sections with different format versions by the linker.
+
+As of now, the only supported format version is described above and has version
+number 0.
+
+Type identifiers
+================
+
+The type for an indirect call or target is the function signature.
+The mapping from a type to an identifier is an ABI detail.
+In the current experimental implementation, an identifier of type T is
+computed as follows:
+
+ - Obtain the generalized mangled name for âtypeinfo name for Tâ.
+ - Compute MD5 hash of the name as a string.
+ - Reinterpret the first 8 bytes of the hash as a little-endian 64-bit integer.
+
+To avoid mismatched pointer types, generalizations are applied.
+Pointers in return and argument types are treated as equivalent as long as the
+qualifiers for the type they point to match.
+For example, ``char*``, ``char**``, and ``int*`` are considered equivalent
+types. However, ``char*`` and ``const char*`` are considered separate types.
+
+Missing type identifiers
+========================
+
+For functions, two cases need to be considered. First, if the compiler cannot
+deduce a type id for an indirect target, it will be listed as an indirect target
+without a type id. Second, if an object without a call graph section gets
+linked, the final call graph section will lack information on functions from
+the object. For completeness, these functions need to be taken as receiver to
+any indirect call regardless of their type id.
+``llvm-objdump --call-graph-info`` lists these functions as indirect targets
+with `UNKNOWN` type id.
+
+For indirect calls, current implementation guarantees a type id for each
+compiled call. However, if an object without a call graph section gets linked,
+no type id will be present for its indirect calls. For completeness, these calls
+need to be taken to target any indirect target regardless of their type id. For
+indirect calls, ``llvm-objdump --call-graph-info`` prints 1) a complete list of
+indirect calls, 2) type id to indirect call mappings. The difference of these
+lists allow to deduce the indirect calls with missing type ids.
+
+TODO: measure and report the ratio of missed type ids
+
+Performance
+===========
+
+A call graph section does not affect the executable code and does not occupy
+memory during process execution. Therefore, there is no performance overhead.
+
+The scheme has not yet been optimized for binary size.
+
+TODO: measure and report the increase in the binary size
+
+Example
+=======
+
+For example, consider the following C++ code:
+
+.. code-block:: cpp
+
+ namespace {
+ // Not an indirect target
+ void foo() {}
+ }
+
+ // Indirect target 1
+ void bar() {}
+
+ // Indirect target 2
+ int baz(char a, float *b) {
+ return 0;
+ }
+
+ // Indirect target 3
+ int main() {
+ char a;
+ float b;
+ void (*fp_bar)() = bar;
+ int (*fp_baz1)(char, float*) = baz;
+ int (*fp_baz2)(char, float*) = baz;
+
+ // Indirect call site 1
+ fp_bar();
+
+ // Indirect call site 2
+ fp_baz1(a, &b);
+
+ // Indirect call site 3: shares the type id with indirect call site 2
+ fp_baz2(a, &b);
+
+ // Direct call sites
+ foo();
+ bar();
+ baz(a, &b);
+
+ return 0;
+ }
+
+Following will compile it with a call graph section created in the binary:
+
+.. code-block:: bash
+
+ $ clang -fcall-graph-section example.cpp
+
+During the construction of the call graph section, the type identifiers are
+computed as follows:
+
++---------------+-----------------------+----------------------------+----------------------------+
+| Function name | Generalized signature | Mangled name (itanium ABI) | Numeric type id (md5 hash) |
++===============+=======================+============================+============================+
+| bar | void () | _ZTSFvvE.generalized | f85c699bb8ef20a2 |
++---------------+-----------------------+----------------------------+----------------------------+
+| baz | int (char, void*) | _ZTSFicPvE.generalized | e3804d2a7f2b03fe |
++---------------+-----------------------+----------------------------+----------------------------+
+| main | int () | _ZTSFivE.generalized | a9494def81a01dc |
++---------------+-----------------------+----------------------------+----------------------------+
+
+The call graph section will have the following content:
+
++---------------+-----------------+--------------+----------------+---------------+--------------------------------------+
+| FormatVersion | FunctionEntryPc | FunctionKind | FunctionTypeId | CallSiteCount | CallSiteList |
++===============+=================+==============+================+===============+======================================+
+| 0 | EntryPc(foo) | 0 | (empty) | 0 | (empty) |
++---------------+-----------------+--------------+----------------+---------------+--------------------------------------+
+| 0 | EntryPc(bar) | 2 | TypeId(bar) | 0 | (empty) |
++---------------+-----------------+--------------+----------------+---------------+--------------------------------------+
+| 0 | EntryPc(baz) | 2 | TypeId(baz) | 0 | (empty) |
++---------------+-----------------+--------------+----------------+---------------+--------------------------------------+
+| 0 | EntryPc(main) | 2 | TypeId(main) | 3 | * TypeId(bar), CallSitePc(fp_bar()) |
+| | | | | | * TypeId(baz), CallSitePc(fp_baz1()) |
+| | | | | | * TypeId(baz), CallSitePc(fp_baz2()) |
++---------------+-----------------+--------------+----------------+---------------+--------------------------------------+
+
+
+The ``llvm-objdump`` utility can parse the call graph section and disassemble
+the program to provide complete call graph information. This includes any
+additional call sites from the binary:
+
+.. code-block:: bash
+
+ $ llvm-objdump --call-graph-info a.out
+
+ # Comments are not a part of the llvm-objdump's output but inserted for clarifications.
+
+ a.out: file format elf64-x86-64
+ # These warnings are due to the functions and the indirect calls coming from linked objects.
+ llvm-objdump: warning: 'a.out': callgraph section does not have type ids for 3 indirect calls
+ llvm-objdump: warning: 'a.out': callgraph section does not have information for 10 functions
+
+ # Unknown targets are the 10 functions the warnings mention.
+ INDIRECT TARGET TYPES (TYPEID [FUNC_ADDR,])
+ UNKNOWN 401000 401100 401234 401050 401090 4010d0 4011d0 401020 401060 401230
+ a9494def81a01dc 401150 # main()
+ f85c699bb8ef20a2 401120 # bar()
+ e3804d2a7f2b03fe 401130 # baz()
+
+ # Notice that the call sites share the same type id as target functions
+ INDIRECT CALL TYPES (TYPEID [CALL_SITE_ADDR,])
+ f85c699bb8ef20a2 401181 # Indirect call site 1 (fp_bar())
+ e3804d2a7f2b03fe 401191 4011a1 # Indirect call site 2 and 3 (fp_baz1() and fp_baz2())
+
+ INDIRECT CALL SITES (CALLER_ADDR [CALL_SITE_ADDR,])
+ 401000 401012 # _init
+ 401150 401181 401191 4011a1 # main calls fp_bar(), fp_baz1(), fp_baz2()
+ 4011d0 401215 # __libc_csu_init
+ 401020 40104a # _start
+
+ DIRECT CALL SITES (CALLER_ADDR [(CALL_SITE_ADDR, TARGET_ADDR),])
+ 4010d0 4010e2 401060 # __do_global_dtors_aux
+ 401150 4011a6 401110 4011ab 401120 4011ba 401130 # main calls foo(), bar(), baz()
+ 4011d0 4011fd 401000 # __libc_csu_init
+
+ FUNCTIONS (FUNC_ENTRY_ADDR, SYM_NAME)
+ 401000 _init
+ 401100 frame_dummy
+ 401234 _fini
+ 401050 _dl_relocate_static_pie
+ 401090 register_tm_clones
+ 4010d0 __do_global_dtors_aux
+ 401110 _ZN12_GLOBAL__N_13fooEv # (anonymous namespace)::foo()
+ 401150 main # main
+ 4011d0 __libc_csu_init
+ 401020 _start
+ 401060 deregister_tm_clones
+ 401120 _Z3barv # bar()
+ 401130 _Z3bazcPf # baz(char, float*)
+ 401230 __libc_csu_fini
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