[llvm] [DWARF] Add option to add linkage_names to call_origin declaration refs (PR #89640)
Orlando Cazalet-Hyams via llvm-commits
llvm-commits at lists.llvm.org
Mon Apr 22 10:58:44 PDT 2024
https://github.com/OCHyams created https://github.com/llvm/llvm-project/pull/89640
If `-mllvm -add-linkage-names-to-external-call-origins` is true then add
`DW_AT_linkage_name` attributes to `DW_TAG_subprogram` DIEs referenced by
`DW_AT_call_origin` attributes that would otherwise be omitted.
---
A debugger may use `DW_TAG_call_origin` attributes to determine whether any
frames in a call stack are missing due to optimisations (e.g. tail calls).
For example, say `a()` calls `b()` tail-calls `c()`, and you stop in your debugger
in `c()`:
The callstack looks like this:
#0 c() <- stopped in this frame
#1 a()
Looking "up" from `c()`, call site information can be found in `a()`. This includes
a DW_AT_call_origin referencing `b()`'s subprogram DIE, which means the call at
this call site was to `b()`, not `c()` where we are currently stopped. This
indicates `b()`'s frame has been lost due to optimisation (or is misleading due
to ICF).
This patch makes it easier for a debugger to check whether the referenced
DIE describes the target function or not, for example by comparing the referenced
function name to the current frame.
---
There's already an option to apply DW_AT_linkage_name in a targeted manner: `-dwarf-linkage-names=Abstract`, which limits adding DW_AT_linkage_names to abstract subprogram DIEs (this is default for SCE tuning).
The new flag shouldn't change anything upstream whether it is enabled or not because the non-SCE-tuned behaviour upstream is to always add linkage names to subprogram DIEs, AFAICT.
Enabling this feature alongside `-dwarf-linkage-names=Abstract` has minimal impact on size of CTMark RelWithDebInfo binaries. There's a geomean increase in size by < 0.1%.
>From 3f3b5cdc3f08d22e7ae4bb3561a78463cc630fab Mon Sep 17 00:00:00 2001
From: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
Date: Thu, 4 Apr 2024 22:14:47 +0100
Subject: [PATCH] [DWARF] Add option to add linkage_names to call_origin
declaration refs
If -mllvm -add-linkage-names-to-external-call-origins is true then add
DW_AT_linkage_name attributes to DW_TAG_subprogram DIEs referenced by
DW_AT_call_origin attributes that would otherwise be omitted.
A debugger may use DW_TAG_call_origin attributes to determine whether any
frames in a callstack are missing due to optimisations (e.g. tail calls).
For example, say a() calls b() tail-calls c(), and you stop in your
debugger in c():
The callstack looks like this:
c()
a()
Looking "up" from c(), call site information can be found in a(). This
includes a DW_AT_call_origin referencing b()'s subprogram DIE, which means
the call at this call site was to b(), not c() where we are currently stopped.
This indicates b()'s frame has been lost due to optimisation (tail call or
ICF).
This patch makes it easier for a debugger to check whether the referenced DIE
describes the target function or not, for example by comparing the referenced
function name to the current frame.
---
.../CodeGen/AsmPrinter/DwarfCompileUnit.cpp | 21 ++++
.../X86/call-origin-linkage-names.ll | 96 +++++++++++++++++++
2 files changed, 117 insertions(+)
create mode 100644 llvm/test/DebugInfo/X86/call-origin-linkage-names.ll
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 14f2a363f9be61..49954bf10abd5b 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -35,6 +35,7 @@
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
+#include "llvm/Support/CommandLine.h"
#include <iterator>
#include <optional>
#include <string>
@@ -42,6 +43,20 @@
using namespace llvm;
+/// Query value using AddLinkageNamesToDeclCallOriginsForTuning.
+cl::opt<cl::boolOrDefault> AddLinkageNamesToDeclCallOrigins(
+ "add-linkage-names-to-declaration-call-origins", cl::Hidden,
+ cl::desc("Add DW_AT_linkage_name to function declaration DIEs "
+ "referenced by DW_AT_call_origin attributes. Enabled by default "
+ "for -gsce debugger tuning."));
+
+static bool AddLinkageNamesToDeclCallOriginsForTuning(const DwarfDebug *DD) {
+ bool EnabledByDefault = DD->tuneForSCE();
+ if (EnabledByDefault)
+ return AddLinkageNamesToDeclCallOrigins != cl::boolOrDefault::BOU_FALSE;
+ return AddLinkageNamesToDeclCallOrigins == cl::boolOrDefault::BOU_TRUE;
+}
+
static dwarf::Tag GetCompileUnitType(UnitKind Kind, DwarfDebug *DW) {
// According to DWARF Debugging Information Format Version 5,
@@ -1260,6 +1275,12 @@ DIE &DwarfCompileUnit::constructCallSiteEntryDIE(DIE &ScopeDIE,
} else {
DIE *CalleeDIE = getOrCreateSubprogramDIE(CalleeSP);
assert(CalleeDIE && "Could not create DIE for call site entry origin");
+ if (AddLinkageNamesToDeclCallOriginsForTuning(DD) &&
+ !CalleeSP->isDefinition() &&
+ !CalleeDIE->findAttribute(dwarf::DW_AT_linkage_name)) {
+ addLinkageName(*CalleeDIE, CalleeSP->getLinkageName());
+ }
+
addDIEEntry(CallSiteDIE, getDwarf5OrGNUAttr(dwarf::DW_AT_call_origin),
*CalleeDIE);
}
diff --git a/llvm/test/DebugInfo/X86/call-origin-linkage-names.ll b/llvm/test/DebugInfo/X86/call-origin-linkage-names.ll
new file mode 100644
index 00000000000000..c8ca3075c0ff7a
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/call-origin-linkage-names.ll
@@ -0,0 +1,96 @@
+; RUN: llc %s --filetype=obj -o - -dwarf-linkage-names=Abstract -add-linkage-names-to-declaration-call-origins=false \
+; RUN: | llvm-dwarfdump - | FileCheck %s --check-prefixes=COMMON,DISABLE --implicit-check-not=DW_AT_linkage_name
+; RUN: llc %s --filetype=obj -o - -dwarf-linkage-names=Abstract -add-linkage-names-to-declaration-call-origins=true \
+; RUN: | llvm-dwarfdump - | FileCheck %s --check-prefixes=COMMON,ENABLE --implicit-check-not=DW_AT_linkage_name
+
+;; Check that -add-linkage-names-to-declaration-call-origins controls whether
+;; linkage names are added to declarations referenced by DW_AT_call_origin
+;; attributes.
+;;
+;; $ cat test.cpp
+;; void a();
+;; __attribute__((optnone))
+;; void b() {}
+;; void c();
+;; extern "C" {
+;; void d();
+;; }
+;;
+;; void e() {
+;; a(); //< Reference declaration DIE (add linkage name).
+;; b(); //< Reference definition DIE (don't add linkage name).
+;; c(); //< Reference definition DIE (don't add linkage name).
+;; d(); //< Reference declaration DIE, but there's no linkage name.
+;; }
+;;
+;; __attribute__((optnone))
+;; void c() {}
+;; $ clang++ -emit-llvm -S -O1 -g
+
+; COMMON: DW_TAG_call_site
+; ENABLE-NEXT: DW_AT_call_origin (0x[[a:[a-z0-9]+]] "_Z1av")
+; DISABLE-NEXT: DW_AT_call_origin (0x[[a:[a-z0-9]+]] "a")
+; COMMON: DW_TAG_call_site
+; COMMON-NEXT: DW_AT_call_origin (0x[[b:[a-z0-9]+]] "b")
+; COMMON: DW_TAG_call_site
+; COMMON-NEXT: DW_AT_call_origin (0x[[c:[a-z0-9]+]] "c")
+; COMMON: DW_TAG_call_site
+; COMMON-NEXT: DW_AT_call_origin (0x[[d:[a-z0-9]+]] "d")
+
+; COMMON: 0x[[a]]: DW_TAG_subprogram
+; COMMON: DW_AT_name ("a")
+; ENABLE: DW_AT_linkage_name ("_Z1av")
+; COMMON: 0x[[b]]: DW_TAG_subprogram
+; COMMON: DW_AT_name ("b")
+; COMMON: 0x[[c]]: DW_TAG_subprogram
+; COMMON: DW_AT_name ("c")
+; COMMON: 0x[[d]]: DW_TAG_subprogram
+; COMMON: DW_AT_name ("d")
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @_Z1ev() local_unnamed_addr !dbg !13 {
+entry:
+ tail call void @_Z1av(), !dbg !14
+ tail call void @_Z1bv(), !dbg !15
+ tail call void @_Z1cv(), !dbg !16
+ tail call void @d(), !dbg !17
+ ret void, !dbg !18
+}
+
+define dso_local void @_Z1bv() local_unnamed_addr !dbg !9 {
+entry:
+ ret void, !dbg !12
+}
+
+declare !dbg !19 void @_Z1av() local_unnamed_addr
+
+define dso_local void @_Z1cv() local_unnamed_addr !dbg !20 {
+entry:
+ ret void, !dbg !21
+}
+declare !dbg !22 void @d() local_unnamed_addr
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 19.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{!"clang version 19.0.0"}
+!9 = distinct !DISubprogram(name: "b", linkageName: "_Z1bv", scope: !1, file: !1, line: 3, type: !10, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!10 = !DISubroutineType(types: !11)
+!11 = !{null}
+!12 = !DILocation(line: 3, column: 11, scope: !9)
+!13 = distinct !DISubprogram(name: "e", linkageName: "_Z1ev", scope: !1, file: !1, line: 9, type: !10, scopeLine: 9, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!14 = !DILocation(line: 10, column: 3, scope: !13)
+!15 = !DILocation(line: 11, column: 3, scope: !13)
+!16 = !DILocation(line: 12, column: 3, scope: !13)
+!17 = !DILocation(line: 13, column: 3, scope: !13)
+!18 = !DILocation(line: 14, column: 1, scope: !13)
+!19 = !DISubprogram(name: "a", linkageName: "_Z1av", scope: !1, file: !1, line: 1, type: !10, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
+!20 = distinct !DISubprogram(name: "c", linkageName: "_Z1cv", scope: !1, file: !1, line: 17, type: !10, scopeLine: 17, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!21 = !DILocation(line: 17, column: 11, scope: !20)
+!22 = !DISubprogram(name: "d", scope: !1, file: !1, line: 6, type: !10, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
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