[MC] Add .loc_label instruction #99710
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@llvm/pr-subscribers-mc Author: None (alx32) ChangesAs discussed in the RFC we need a way to create labels in the assembler-generated line section in order to support the future addition of the DW_AT_LLVM_stmt_sequence attribute. We have a similar precedent for such behavior with the .cfi_label instruction - so we add the
Full diff: https://github.com/llvm/llvm-project/pull/99710.diff 7 Files Affected:
diff --git a/llvm/include/llvm/MC/MCDwarf.h b/llvm/include/llvm/MC/MCDwarf.h
index d0e45ab59a92e..7ac9c2e023617 100644
--- a/llvm/include/llvm/MC/MCDwarf.h
+++ b/llvm/include/llvm/MC/MCDwarf.h
@@ -194,11 +194,17 @@ class MCDwarfLineEntry : public MCDwarfLoc {
public:
// Constructor to create an MCDwarfLineEntry given a symbol and the dwarf loc.
- MCDwarfLineEntry(MCSymbol *label, const MCDwarfLoc loc)
- : MCDwarfLoc(loc), Label(label) {}
+ MCDwarfLineEntry(MCSymbol *label, const MCDwarfLoc loc,
+ MCSymbol *lineStreamLabel = nullptr)
+ : MCDwarfLoc(loc), Label(label), LineStreamLabel(lineStreamLabel) {}
MCSymbol *getLabel() const { return Label; }
+ // This is the label that is to be emmited into the line stream. If this is
+ // non-null and we need to emit a label, also make sure to restart the current
+ // line sequence.
+ MCSymbol *LineStreamLabel;
+
// This indicates the line entry is synthesized for an end entry.
bool IsEndEntry = false;
diff --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
index 78aa12062102c..5fe4534d11d8e 100644
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -912,6 +912,9 @@ class MCStreamer {
unsigned Isa, unsigned Discriminator,
StringRef FileName);
+ /// This implements the '.loc_label Name' directive.
+ virtual void emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name);
+
/// Associate a filename with a specified logical file number, and also
/// specify that file's checksum information. This implements the '.cv_file 4
/// "foo.c"' assembler directive. Returns true on success.
diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index 45c32f13e759b..89a4aaf47fcd7 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -285,6 +285,8 @@ class MCAsmStreamer final : public MCStreamer {
unsigned Flags, unsigned Isa,
unsigned Discriminator,
StringRef FileName) override;
+ virtual void emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) override;
+
MCSymbol *getDwarfLineTableSymbol(unsigned CUID) override;
bool emitCVFileDirective(unsigned FileNo, StringRef Filename,
@@ -1751,6 +1753,12 @@ void MCAsmStreamer::emitDwarfLocDirective(unsigned FileNo, unsigned Line,
Discriminator, FileName);
}
+void MCAsmStreamer::emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) {
+ MCStreamer::emitDwarfLocLabelDirective(Loc, Name);
+ OS << "\t.loc_label " << Name;
+ EmitEOL();
+}
+
MCSymbol *MCAsmStreamer::getDwarfLineTableSymbol(unsigned CUID) {
// Always use the zeroth line table, since asm syntax only supports one line
// table for now.
diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index efafd555c5c5c..4355b7b078e89 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -172,6 +172,7 @@ void MCDwarfLineTable::emitOne(
const MCLineSection::MCDwarfLineEntryCollection &LineEntries) {
unsigned FileNum, LastLine, Column, Flags, Isa, Discriminator;
+ bool IsAtStartSeq;
MCSymbol *LastLabel;
auto init = [&]() {
FileNum = 1;
@@ -181,6 +182,7 @@ void MCDwarfLineTable::emitOne(
Isa = 0;
Discriminator = 0;
LastLabel = nullptr;
+ IsAtStartSeq = true;
};
init();
@@ -189,11 +191,24 @@ void MCDwarfLineTable::emitOne(
for (const MCDwarfLineEntry &LineEntry : LineEntries) {
MCSymbol *Label = LineEntry.getLabel();
const MCAsmInfo *asmInfo = MCOS->getContext().getAsmInfo();
+
+ if (LineEntry.LineStreamLabel) {
+ if (!IsAtStartSeq) {
+ MCOS->emitDwarfLineEndEntry(Section, LastLabel);
+ init();
+ }
+ MCOS->emitLabel(LineEntry.LineStreamLabel);
+
+ IsAtStartSeq = true;
+ continue;
+ }
+
if (LineEntry.IsEndEntry) {
MCOS->emitDwarfAdvanceLineAddr(INT64_MAX, LastLabel, Label,
asmInfo->getCodePointerSize());
init();
EndEntryEmitted = true;
+ IsAtStartSeq = true;
continue;
}
@@ -243,6 +258,7 @@ void MCDwarfLineTable::emitOne(
Discriminator = 0;
LastLine = LineEntry.getLine();
LastLabel = Label;
+ IsAtStartSeq = false;
}
// Generate DWARF line end entry.
@@ -250,7 +266,7 @@ void MCDwarfLineTable::emitOne(
// table using ranges whenever CU or section changes. However, the MC path
// does not track ranges nor terminate the line table. In that case,
// conservatively use the section end symbol to end the line table.
- if (!EndEntryEmitted)
+ if (!EndEntryEmitted && !IsAtStartSeq)
MCOS->emitDwarfLineEndEntry(Section, LastLabel);
}
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index d05712bca73cd..2db7881342ca4 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -485,6 +485,7 @@ class AsmParser : public MCAsmParser {
DK_FILE,
DK_LINE,
DK_LOC,
+ DK_LOC_LABEL,
DK_STABS,
DK_CV_FILE,
DK_CV_FUNC_ID,
@@ -580,10 +581,11 @@ class AsmParser : public MCAsmParser {
// ".align{,32}", ".p2align{,w,l}"
bool parseDirectiveAlign(bool IsPow2, unsigned ValueSize);
- // ".file", ".line", ".loc", ".stabs"
+ // ".file", ".line", ".loc", ".loc_label", ".stabs"
bool parseDirectiveFile(SMLoc DirectiveLoc);
bool parseDirectiveLine();
bool parseDirectiveLoc();
+ bool parseDirectiveLocLabel(SMLoc DirectiveLoc);
bool parseDirectiveStabs();
// ".cv_file", ".cv_func_id", ".cv_inline_site_id", ".cv_loc", ".cv_linetable",
@@ -2156,6 +2158,8 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
return parseDirectiveLine();
case DK_LOC:
return parseDirectiveLoc();
+ case DK_LOC_LABEL:
+ return parseDirectiveLocLabel(IDLoc);
case DK_STABS:
return parseDirectiveStabs();
case DK_CV_FILE:
@@ -3737,6 +3741,19 @@ bool AsmParser::parseDirectiveLoc() {
return false;
}
+/// parseDirectiveLoc
+/// ::= .loc_label label
+bool AsmParser::parseDirectiveLocLabel(SMLoc DirectiveLoc) {
+ StringRef Name;
+ DirectiveLoc = Lexer.getLoc();
+ if (parseIdentifier(Name))
+ return TokError("expected identifier");
+ if (parseEOL())
+ return true;
+ getStreamer().emitDwarfLocLabelDirective(DirectiveLoc, Name);
+ return false;
+}
+
/// parseDirectiveStabs
/// ::= .stabs string, number, number, number
bool AsmParser::parseDirectiveStabs() {
@@ -5549,6 +5566,7 @@ void AsmParser::initializeDirectiveKindMap() {
DirectiveKindMap[".file"] = DK_FILE;
DirectiveKindMap[".line"] = DK_LINE;
DirectiveKindMap[".loc"] = DK_LOC;
+ DirectiveKindMap[".loc_label"] = DK_LOC_LABEL;
DirectiveKindMap[".stabs"] = DK_STABS;
DirectiveKindMap[".cv_file"] = DK_CV_FILE;
DirectiveKindMap[".cv_func_id"] = DK_CV_FUNC_ID;
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 1594bd3231abe..d5f323129c4dd 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -267,6 +267,25 @@ void MCStreamer::emitDwarfLocDirective(unsigned FileNo, unsigned Line,
Discriminator);
}
+void MCStreamer::emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) {
+ auto &ctx = getContext();
+
+ auto *LineStreamLabel = ctx.getOrCreateSymbol(Name);
+
+ auto *LineSym = ctx.createTempSymbol();
+ const MCDwarfLoc &DwarfLoc = ctx.getCurrentDwarfLoc();
+
+ // Create a 'fake' line entry by having LineStreamLabel be non-null. This
+ // won't actually emit any line information, it will reset the line table
+ // sequence and emit a label at the start of the new line table sequence.
+ MCDwarfLineEntry LineEntry(LineSym, DwarfLoc, LineStreamLabel);
+
+ // Add the line entry to this section's entries.
+ ctx.getMCDwarfLineTable(ctx.getDwarfCompileUnitID())
+ .getMCLineSections()
+ .addLineEntry(LineEntry, getCurrentSectionOnly());
+}
+
MCSymbol *MCStreamer::getDwarfLineTableSymbol(unsigned CUID) {
MCDwarfLineTable &Table = getContext().getMCDwarfLineTable(CUID);
if (!Table.getLabel()) {
diff --git a/llvm/test/MC/ELF/debug-loc-label.s b/llvm/test/MC/ELF/debug-loc-label.s
new file mode 100644
index 0000000000000..dabf470d417cc
--- /dev/null
+++ b/llvm/test/MC/ELF/debug-loc-label.s
@@ -0,0 +1,74 @@
+// Verify that the .loc_label instruction resets the line sequence and generates
+// the requested label at the correct position in the line stream
+
+// RUN: llvm-mc -filetype obj -triple x86_64-linux-elf %s -o %t.o
+// RUN: llvm-objdump -d %t.o | FileCheck %s --check-prefix=CHECK-ASM
+// RUN: llvm-dwarfdump -v --debug-line %t.o | FileCheck %s --check-prefix=CHECK-LINE-TABLE
+
+# CHECK-ASM: <foo>:
+# CHECK-ASM-NEXT: movq %rdx, 0x33
+# CHECK-ASM-NEXT: movq %rax, 0x3b
+# CHECK-ASM-NEXT: movq %rbx, 0x4e
+# CHECK-ASM-NEXT: movq %rcx, 0x60
+# CHECK-ASM-NEXT: retq
+
+# CHECK-LINE-TABLE: Address Line Column File ISA Discriminator OpIndex Flags
+# CHECK-LINE-TABLE-NEXT: ------------------ ------ ------ ------ --- ------------- ------- -------------
+# CHECK-LINE-TABLE-NEXT: 0x00000028: 05 DW_LNS_set_column (1)
+# CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000)
+# CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000000 1 1 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x00000036: 02 DW_LNS_advance_pc (addr += 33, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x00000038: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 1 1 0 0 0 is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000003b: 05 DW_LNS_set_column (2)
+# CHECK-LINE-TABLE-NEXT: 0x0000003d: 00 DW_LNE_set_address (0x0000000000000008)
+# CHECK-LINE-TABLE-NEXT: 0x00000048: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000008 1 2 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x00000049: 02 DW_LNS_advance_pc (addr += 25, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x0000004b: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 2 1 0 0 0 is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000004e: 05 DW_LNS_set_column (3)
+# CHECK-LINE-TABLE-NEXT: 0x00000050: 00 DW_LNE_set_address (0x0000000000000010)
+# CHECK-LINE-TABLE-NEXT: 0x0000005b: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000010 1 3 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x0000005c: 08 DW_LNS_const_add_pc (addr += 0x0000000000000011, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x0000005d: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 3 1 0 0 0 is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x00000060: 05 DW_LNS_set_column (4)
+# CHECK-LINE-TABLE-NEXT: 0x00000062: 00 DW_LNE_set_address (0x0000000000000018)
+# CHECK-LINE-TABLE-NEXT: 0x0000006d: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000018 1 4 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x0000006e: 05 DW_LNS_set_column (5)
+# CHECK-LINE-TABLE-NEXT: 0x00000070: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000018 1 5 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x00000071: 02 DW_LNS_advance_pc (addr += 9, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x00000073: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 5 1 0 0 0 is_stmt end_sequence
+ .text
+ .file "test.c"
+ .globl foo
+ .align 16, 0x90
+ .type foo,@function
+foo:
+.Lfunc_begin0:
+ .file 1 "test.c"
+ .cfi_startproc
+ .loc 1 1 1
+ mov %rdx, 0x33
+ .loc_label my_label_02
+ .loc 1 1 2
+ movq %rax, my_label_02-.Lline_table_start0
+ .loc 1 1 3
+ .loc_label my_label_03
+ .loc_label my_label_03.1
+ movq %rbx, my_label_03-.Lline_table_start0
+ .loc 1 1 4
+ .loc_label my_label_05
+ .loc 1 1 5
+ movq %rcx, my_label_05-.Lline_table_start0
+ ret
+ .cfi_endproc
+
+ .section .debug_line,"",@progbits
+.Lline_table_start0:
|
|
@llvm/pr-subscribers-debuginfo Author: None (alx32) ChangesAs discussed in the RFC we need a way to create labels in the assembler-generated line section in order to support the future addition of the DW_AT_LLVM_stmt_sequence attribute. We have a similar precedent for such behavior with the .cfi_label instruction - so we add the
Full diff: https://github.com/llvm/llvm-project/pull/99710.diff 7 Files Affected:
diff --git a/llvm/include/llvm/MC/MCDwarf.h b/llvm/include/llvm/MC/MCDwarf.h
index d0e45ab59a92e..7ac9c2e023617 100644
--- a/llvm/include/llvm/MC/MCDwarf.h
+++ b/llvm/include/llvm/MC/MCDwarf.h
@@ -194,11 +194,17 @@ class MCDwarfLineEntry : public MCDwarfLoc {
public:
// Constructor to create an MCDwarfLineEntry given a symbol and the dwarf loc.
- MCDwarfLineEntry(MCSymbol *label, const MCDwarfLoc loc)
- : MCDwarfLoc(loc), Label(label) {}
+ MCDwarfLineEntry(MCSymbol *label, const MCDwarfLoc loc,
+ MCSymbol *lineStreamLabel = nullptr)
+ : MCDwarfLoc(loc), Label(label), LineStreamLabel(lineStreamLabel) {}
MCSymbol *getLabel() const { return Label; }
+ // This is the label that is to be emmited into the line stream. If this is
+ // non-null and we need to emit a label, also make sure to restart the current
+ // line sequence.
+ MCSymbol *LineStreamLabel;
+
// This indicates the line entry is synthesized for an end entry.
bool IsEndEntry = false;
diff --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
index 78aa12062102c..5fe4534d11d8e 100644
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -912,6 +912,9 @@ class MCStreamer {
unsigned Isa, unsigned Discriminator,
StringRef FileName);
+ /// This implements the '.loc_label Name' directive.
+ virtual void emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name);
+
/// Associate a filename with a specified logical file number, and also
/// specify that file's checksum information. This implements the '.cv_file 4
/// "foo.c"' assembler directive. Returns true on success.
diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index 45c32f13e759b..89a4aaf47fcd7 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -285,6 +285,8 @@ class MCAsmStreamer final : public MCStreamer {
unsigned Flags, unsigned Isa,
unsigned Discriminator,
StringRef FileName) override;
+ virtual void emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) override;
+
MCSymbol *getDwarfLineTableSymbol(unsigned CUID) override;
bool emitCVFileDirective(unsigned FileNo, StringRef Filename,
@@ -1751,6 +1753,12 @@ void MCAsmStreamer::emitDwarfLocDirective(unsigned FileNo, unsigned Line,
Discriminator, FileName);
}
+void MCAsmStreamer::emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) {
+ MCStreamer::emitDwarfLocLabelDirective(Loc, Name);
+ OS << "\t.loc_label " << Name;
+ EmitEOL();
+}
+
MCSymbol *MCAsmStreamer::getDwarfLineTableSymbol(unsigned CUID) {
// Always use the zeroth line table, since asm syntax only supports one line
// table for now.
diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index efafd555c5c5c..4355b7b078e89 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -172,6 +172,7 @@ void MCDwarfLineTable::emitOne(
const MCLineSection::MCDwarfLineEntryCollection &LineEntries) {
unsigned FileNum, LastLine, Column, Flags, Isa, Discriminator;
+ bool IsAtStartSeq;
MCSymbol *LastLabel;
auto init = [&]() {
FileNum = 1;
@@ -181,6 +182,7 @@ void MCDwarfLineTable::emitOne(
Isa = 0;
Discriminator = 0;
LastLabel = nullptr;
+ IsAtStartSeq = true;
};
init();
@@ -189,11 +191,24 @@ void MCDwarfLineTable::emitOne(
for (const MCDwarfLineEntry &LineEntry : LineEntries) {
MCSymbol *Label = LineEntry.getLabel();
const MCAsmInfo *asmInfo = MCOS->getContext().getAsmInfo();
+
+ if (LineEntry.LineStreamLabel) {
+ if (!IsAtStartSeq) {
+ MCOS->emitDwarfLineEndEntry(Section, LastLabel);
+ init();
+ }
+ MCOS->emitLabel(LineEntry.LineStreamLabel);
+
+ IsAtStartSeq = true;
+ continue;
+ }
+
if (LineEntry.IsEndEntry) {
MCOS->emitDwarfAdvanceLineAddr(INT64_MAX, LastLabel, Label,
asmInfo->getCodePointerSize());
init();
EndEntryEmitted = true;
+ IsAtStartSeq = true;
continue;
}
@@ -243,6 +258,7 @@ void MCDwarfLineTable::emitOne(
Discriminator = 0;
LastLine = LineEntry.getLine();
LastLabel = Label;
+ IsAtStartSeq = false;
}
// Generate DWARF line end entry.
@@ -250,7 +266,7 @@ void MCDwarfLineTable::emitOne(
// table using ranges whenever CU or section changes. However, the MC path
// does not track ranges nor terminate the line table. In that case,
// conservatively use the section end symbol to end the line table.
- if (!EndEntryEmitted)
+ if (!EndEntryEmitted && !IsAtStartSeq)
MCOS->emitDwarfLineEndEntry(Section, LastLabel);
}
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index d05712bca73cd..2db7881342ca4 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -485,6 +485,7 @@ class AsmParser : public MCAsmParser {
DK_FILE,
DK_LINE,
DK_LOC,
+ DK_LOC_LABEL,
DK_STABS,
DK_CV_FILE,
DK_CV_FUNC_ID,
@@ -580,10 +581,11 @@ class AsmParser : public MCAsmParser {
// ".align{,32}", ".p2align{,w,l}"
bool parseDirectiveAlign(bool IsPow2, unsigned ValueSize);
- // ".file", ".line", ".loc", ".stabs"
+ // ".file", ".line", ".loc", ".loc_label", ".stabs"
bool parseDirectiveFile(SMLoc DirectiveLoc);
bool parseDirectiveLine();
bool parseDirectiveLoc();
+ bool parseDirectiveLocLabel(SMLoc DirectiveLoc);
bool parseDirectiveStabs();
// ".cv_file", ".cv_func_id", ".cv_inline_site_id", ".cv_loc", ".cv_linetable",
@@ -2156,6 +2158,8 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
return parseDirectiveLine();
case DK_LOC:
return parseDirectiveLoc();
+ case DK_LOC_LABEL:
+ return parseDirectiveLocLabel(IDLoc);
case DK_STABS:
return parseDirectiveStabs();
case DK_CV_FILE:
@@ -3737,6 +3741,19 @@ bool AsmParser::parseDirectiveLoc() {
return false;
}
+/// parseDirectiveLoc
+/// ::= .loc_label label
+bool AsmParser::parseDirectiveLocLabel(SMLoc DirectiveLoc) {
+ StringRef Name;
+ DirectiveLoc = Lexer.getLoc();
+ if (parseIdentifier(Name))
+ return TokError("expected identifier");
+ if (parseEOL())
+ return true;
+ getStreamer().emitDwarfLocLabelDirective(DirectiveLoc, Name);
+ return false;
+}
+
/// parseDirectiveStabs
/// ::= .stabs string, number, number, number
bool AsmParser::parseDirectiveStabs() {
@@ -5549,6 +5566,7 @@ void AsmParser::initializeDirectiveKindMap() {
DirectiveKindMap[".file"] = DK_FILE;
DirectiveKindMap[".line"] = DK_LINE;
DirectiveKindMap[".loc"] = DK_LOC;
+ DirectiveKindMap[".loc_label"] = DK_LOC_LABEL;
DirectiveKindMap[".stabs"] = DK_STABS;
DirectiveKindMap[".cv_file"] = DK_CV_FILE;
DirectiveKindMap[".cv_func_id"] = DK_CV_FUNC_ID;
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 1594bd3231abe..d5f323129c4dd 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -267,6 +267,25 @@ void MCStreamer::emitDwarfLocDirective(unsigned FileNo, unsigned Line,
Discriminator);
}
+void MCStreamer::emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) {
+ auto &ctx = getContext();
+
+ auto *LineStreamLabel = ctx.getOrCreateSymbol(Name);
+
+ auto *LineSym = ctx.createTempSymbol();
+ const MCDwarfLoc &DwarfLoc = ctx.getCurrentDwarfLoc();
+
+ // Create a 'fake' line entry by having LineStreamLabel be non-null. This
+ // won't actually emit any line information, it will reset the line table
+ // sequence and emit a label at the start of the new line table sequence.
+ MCDwarfLineEntry LineEntry(LineSym, DwarfLoc, LineStreamLabel);
+
+ // Add the line entry to this section's entries.
+ ctx.getMCDwarfLineTable(ctx.getDwarfCompileUnitID())
+ .getMCLineSections()
+ .addLineEntry(LineEntry, getCurrentSectionOnly());
+}
+
MCSymbol *MCStreamer::getDwarfLineTableSymbol(unsigned CUID) {
MCDwarfLineTable &Table = getContext().getMCDwarfLineTable(CUID);
if (!Table.getLabel()) {
diff --git a/llvm/test/MC/ELF/debug-loc-label.s b/llvm/test/MC/ELF/debug-loc-label.s
new file mode 100644
index 0000000000000..dabf470d417cc
--- /dev/null
+++ b/llvm/test/MC/ELF/debug-loc-label.s
@@ -0,0 +1,74 @@
+// Verify that the .loc_label instruction resets the line sequence and generates
+// the requested label at the correct position in the line stream
+
+// RUN: llvm-mc -filetype obj -triple x86_64-linux-elf %s -o %t.o
+// RUN: llvm-objdump -d %t.o | FileCheck %s --check-prefix=CHECK-ASM
+// RUN: llvm-dwarfdump -v --debug-line %t.o | FileCheck %s --check-prefix=CHECK-LINE-TABLE
+
+# CHECK-ASM: <foo>:
+# CHECK-ASM-NEXT: movq %rdx, 0x33
+# CHECK-ASM-NEXT: movq %rax, 0x3b
+# CHECK-ASM-NEXT: movq %rbx, 0x4e
+# CHECK-ASM-NEXT: movq %rcx, 0x60
+# CHECK-ASM-NEXT: retq
+
+# CHECK-LINE-TABLE: Address Line Column File ISA Discriminator OpIndex Flags
+# CHECK-LINE-TABLE-NEXT: ------------------ ------ ------ ------ --- ------------- ------- -------------
+# CHECK-LINE-TABLE-NEXT: 0x00000028: 05 DW_LNS_set_column (1)
+# CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000)
+# CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000000 1 1 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x00000036: 02 DW_LNS_advance_pc (addr += 33, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x00000038: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 1 1 0 0 0 is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000003b: 05 DW_LNS_set_column (2)
+# CHECK-LINE-TABLE-NEXT: 0x0000003d: 00 DW_LNE_set_address (0x0000000000000008)
+# CHECK-LINE-TABLE-NEXT: 0x00000048: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000008 1 2 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x00000049: 02 DW_LNS_advance_pc (addr += 25, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x0000004b: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 2 1 0 0 0 is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000004e: 05 DW_LNS_set_column (3)
+# CHECK-LINE-TABLE-NEXT: 0x00000050: 00 DW_LNE_set_address (0x0000000000000010)
+# CHECK-LINE-TABLE-NEXT: 0x0000005b: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000010 1 3 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x0000005c: 08 DW_LNS_const_add_pc (addr += 0x0000000000000011, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x0000005d: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 3 1 0 0 0 is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x00000060: 05 DW_LNS_set_column (4)
+# CHECK-LINE-TABLE-NEXT: 0x00000062: 00 DW_LNE_set_address (0x0000000000000018)
+# CHECK-LINE-TABLE-NEXT: 0x0000006d: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000018 1 4 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x0000006e: 05 DW_LNS_set_column (5)
+# CHECK-LINE-TABLE-NEXT: 0x00000070: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000018 1 5 1 0 0 0 is_stmt
+# CHECK-LINE-TABLE-NEXT: 0x00000071: 02 DW_LNS_advance_pc (addr += 9, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x00000073: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000000000000021 1 5 1 0 0 0 is_stmt end_sequence
+ .text
+ .file "test.c"
+ .globl foo
+ .align 16, 0x90
+ .type foo,@function
+foo:
+.Lfunc_begin0:
+ .file 1 "test.c"
+ .cfi_startproc
+ .loc 1 1 1
+ mov %rdx, 0x33
+ .loc_label my_label_02
+ .loc 1 1 2
+ movq %rax, my_label_02-.Lline_table_start0
+ .loc 1 1 3
+ .loc_label my_label_03
+ .loc_label my_label_03.1
+ movq %rbx, my_label_03-.Lline_table_start0
+ .loc 1 1 4
+ .loc_label my_label_05
+ .loc 1 1 5
+ movq %rcx, my_label_05-.Lline_table_start0
+ ret
+ .cfi_endproc
+
+ .section .debug_line,"",@progbits
+.Lline_table_start0:
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pogo59
reviewed
Jul 22, 2024
I wanted to test them as they would be used in the future - via relative offsets to the line table start. So for example for And then the tests checks that this gets assembled to: And the test also checks that offset 0x3b in the line table is indeed column 2: I can add additional tests using Note, in the future the offsets would be used with |
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You could emit the label difference into some other attribute in assembly rather than in an instruction (guess that's not necessarily better - it'll necessarily be a bogus attribute/value combination I guess) - or I guess just into its own section and dump the bytes of the section raw... Guess you could use an unknown/bogus attribute number, I think it'd still dump OK & we'd just print a bogus attribute number in the attribute name somehow... - mixed feelings about what the best way to do that is. |
MaskRay
reviewed
Jul 28, 2024
alx32
commented
Jul 29, 2024
pogo59
reviewed
Jul 29, 2024
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The latest update should address all issues - would you have another look please, @pogo59, @MaskRay, @dwblaikie. Thanks! |
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Would be great if we could get this reviewed soon in order to proceed with adding the same functionality to clang. |
MaskRay
reviewed
Aug 19, 2024
llvm/lib/MC/MCAsmStreamer.cpp
Outdated
| @@ -1767,6 +1770,12 @@ void MCAsmStreamer::emitDwarfLocDirective(unsigned FileNo, unsigned Line, | |||
| Discriminator, FileName); | |||
| } | |||
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| void MCAsmStreamer::emitDwarfLocLabelDirective(SMLoc Loc, StringRef Name) { | |||
| MCStreamer::emitDwarfLocLabelDirective(Loc, Name); | |||
| OS << "\t.loc_label " << Name; | |||
| } | ||
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| // Generate DWARF line end entry. | ||
| // We do not need this for DwarfDebug that explicitly terminates the line | ||
| // table using ranges whenever CU or section changes. However, the MC path | ||
| // does not track ranges nor terminate the line table. In that case, | ||
| // conservatively use the section end symbol to end the line table. | ||
| if (!EndEntryEmitted) | ||
| if (!EndEntryEmitted && !IsAtStartSeq) |
There was a problem hiding this comment.
Missing test coverage: the test doesn't fail if I remove && !IsAtStartSeq
It's usually better to inspect the symbol table with |
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@MaskRay I think current version addresses all the comments - could you have another look ? |
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@MaskRay - Could you have another look - trying to finish this to proceed with the clang side of this. |
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@pogo59, @dwblaikie - Could you have a look ? |
MaskRay
approved these changes
Sep 20, 2024
llvm/test/MC/ELF/debug-loc-label.s
Outdated
| // Verify that the .loc_label instruction resets the line sequence and generates | ||
| // the requested label at the correct position in the line stream | ||
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| // RUN: llvm-mc -filetype obj -triple x86_64-linux-elf %s -o %t.o |
There was a problem hiding this comment.
Just -triple x86_64 to make it clear that this is generic ELF behavior, not specific to Linux.
linux-elf is kinda incorrect triple. When the os is linux, "elf" should not be used.
added 6 commits
September 19, 2024 19:13
alx32
added a commit
that referenced
this pull request
Nov 14, 2024
…nces (#110192) **Summary** This patch introduces a new compiler option `-mllvm -emit-func-debug-line-table-offsets` that enables the emission of per-function line table offsets and end sequences in DWARF debug information. This enhancement allows tools and debuggers to accurately attribute line number information to their corresponding functions, even in scenarios where functions are merged or share the same address space due to optimizations like Identical Code Folding (ICF) in the linker. **Background** RFC: [New DWARF Attribute for Symbolication of Merged Functions](https://discourse.llvm.org/t/rfc-new-dwarf-attribute-for-symbolication-of-merged-functions/79434) Previous similar PR: [#93137](#93137) – This PR was very similar to the current one but at the time, the assembler had no support for emitting labels within the line table. That support was added in PR [#99710](#99710) - and in this PR we use some of the support added in the assembler PR. In the current implementation, Clang generates line information in the `debug_line` section without directly associating line entries with their originating `DW_TAG_subprogram` DIEs. This can lead to issues when post-compilation optimizations merge functions, resulting in overlapping address ranges and ambiguous line information. For example, when functions are merged by ICF in LLD, multiple functions may end up sharing the same address range. Without explicit linkage between functions and their line entries, tools cannot accurately attribute line information to the correct function, adversely affecting debugging and call stack resolution. **Implementation Details** To address the above issue, the patch makes the following key changes: **`DW_AT_LLVM_stmt_sequence` Attribute**: Introduces a new LLVM-specific attribute `DW_AT_LLVM_stmt_sequence` to each `DW_TAG_subprogram` DIE. This attribute holds a label pointing to the offset in the line table where the function's line entries begin. **End-of-Sequence Markers**: Emits an explicit DW_LNE_end_sequence after each function's line entries in the line table. This marks the end of the line information for that function, ensuring that line entries are correctly delimited. **Assembler and Streamer Modifications**: Modifies the MCStreamer and related classes to support emitting the necessary labels and tracking the current function's line entries. A new flag GenerateFuncLineTableOffsets is added to control this behavior. **Compiler Option**: Introduces the `-mllvm -emit-func-debug-line-table-offsets` option to enable this functionality, allowing users to opt-in as needed.
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As discussed in the RFC we need a way to create labels in the assembler-generated line section in order to support the future addition of the DW_AT_LLVM_stmt_sequence attribute.
We have a similar precedent for such behavior with the .cfi_label instruction - so we add the
.loc_label THE_LABEL_NAMEinstruction which:.debug_linesection