[lld] [lld][ELF] Introduce an option to keep data section prefix. (PR #148985)
Mingming Liu via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 4 14:25:18 PDT 2025
https://github.com/mingmingl-llvm updated https://github.com/llvm/llvm-project/pull/148985
>From 24c1c62b584fb42fcd91b9343bbe61e521038dd0 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Sun, 30 Mar 2025 23:32:41 +0000
Subject: [PATCH 1/8] lld keep data section prefix
---
lld/ELF/Config.h | 1 +
lld/ELF/Driver.cpp | 4 +++
lld/ELF/LinkerScript.cpp | 69 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 74 insertions(+)
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 03b3cd4771f49..0a01eddf20271 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -372,6 +372,7 @@ struct Config {
bool zInitfirst;
bool zInterpose;
bool zKeepTextSectionPrefix;
+ bool zKeepDataSectionPrefix;
bool zLrodataAfterBss;
bool zNoBtCfi;
bool zNodefaultlib;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 0a220432333cc..32ebd7a1a2ad9 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -1566,6 +1566,10 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
ctx.arg.zInterpose = hasZOption(args, "interpose");
ctx.arg.zKeepTextSectionPrefix = getZFlag(
args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
+ ctx.arg.zKeepDataSectionPrefix = getZFlag(
+ args, "keep-data-section-prefix", "nokeep-data-section-prefix", false);
+ errs() << "ELF/Driver.cpp:1540\t" << ctx.arg.zKeepDataSectionPrefix << "\n";
+
ctx.arg.zLrodataAfterBss =
getZFlag(args, "lrodata-after-bss", "nolrodata-after-bss", false);
ctx.arg.zNoBtCfi = hasZOption(args, "nobtcfi");
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index e19823f2ea752..17432e65bb1bf 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -48,6 +48,11 @@ static bool isSectionPrefix(StringRef prefix, StringRef name) {
return name.consume_front(prefix) && (name.empty() || name[0] == '.');
}
+bool hasUnlikelySuffix(StringRef name) {
+ return name.ends_with(".unlikely") || name.ends_with(".unlikely.") ||
+ name.ends_with("unlikely");
+}
+
StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
// This is for --emit-relocs and -r. If .text.foo is emitted as .text.bar, we
// want to emit .rela.text.foo as .rela.text.bar for consistency (this is not
@@ -105,6 +110,70 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
return ".text";
}
+ if (isSectionPrefix(".data.rel.ro", s->name)) {
+ // Map input sections' .rodata and rodata.hot into .rodata.hot in the
+ // output. Map input sections' .rodata.unlikely into .rodata in the output.
+ if (ctx.arg.zKeepDataSectionPrefix) {
+ if (isSectionPrefix(".data.rel.ro.unlikely", s->name) ||
+ hasUnlikelySuffix(s->name)) {
+ return ".data.rel.ro.unlikely";
+ }
+
+ return ".data.rel.ro";
+ }
+ return ".data.rel.ro";
+ }
+
+ if (isSectionPrefix(".data", s->name)) {
+ // Map input sections' .rodata and rodata.hot into .rodata.hot in the
+ // output. Map input sections' .rodata.unlikely into .rodata in the output.
+ if (ctx.arg.zKeepDataSectionPrefix) {
+ if (isSectionPrefix(".data.unlikely", s->name) ||
+ hasUnlikelySuffix(s->name)) {
+ // errs() << "LinkerScript.cpp:100\t" << s->name << "\n";
+ return ".data.unlikely";
+ }
+
+ return ".data";
+ }
+ return ".data";
+ }
+
+ if (isSectionPrefix(".rodata", s->name)) {
+ // Map input sections' .rodata and rodata.hot into .rodata.hot in the
+ // output. Map input sections' .rodata.unlikely into .rodata in the output.
+ if (ctx.arg.zKeepDataSectionPrefix) {
+ // if (isSectionPrefix(".rodata.cst", s->name)) {
+ // errs() << "LinkerScript.cpp:100\t" << s->name << "\n";
+ //}
+ // .rodata.cst<N>.unlikely
+ // .rodata.str4.16.unlikely
+ if (isSectionPrefix(".rodata.unlikely", s->name) ||
+ hasUnlikelySuffix(s->name)) {
+ // return ".rodata.unlikely";
+ return ".rodata.unlikely";
+ }
+ return ".rodata";
+ }
+ return ".rodata";
+ }
+
+ if (isSectionPrefix(".bss.rel.ro", s->name)) {
+ return ".bss.rel.ro";
+ }
+
+ if (isSectionPrefix(".bss", s->name)) {
+ if (ctx.arg.zKeepDataSectionPrefix) {
+ if (isSectionPrefix(".bss.unlikely", s->name)) {
+ // errs() << "LinkerScript.cpp:100\t" << s->name << "\n";
+ return ".bss.unlikely";
+ }
+
+ return ".bss";
+ }
+ return ".bss";
+ }
+
for (StringRef v : {".data.rel.ro", ".data", ".rodata",
".bss.rel.ro", ".bss", ".ldata",
".lrodata", ".lbss", ".gcc_except_table",
>From 6328b71a44ebe50babcf766f9258df1f0dd8bb3d Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Sun, 20 Jul 2025 18:22:20 -0700
Subject: [PATCH 2/8] simplify implementation
---
lld/ELF/Config.h | 2 +-
lld/ELF/Driver.cpp | 5 +-
lld/ELF/LinkerScript.cpp | 99 ++++++++++++----------------------------
3 files changed, 33 insertions(+), 73 deletions(-)
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 0a01eddf20271..d3f6103fde4b7 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -371,8 +371,8 @@ struct Config {
bool zIfuncNoplt;
bool zInitfirst;
bool zInterpose;
- bool zKeepTextSectionPrefix;
bool zKeepDataSectionPrefix;
+ bool zKeepTextSectionPrefix;
bool zLrodataAfterBss;
bool zNoBtCfi;
bool zNodefaultlib;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 32ebd7a1a2ad9..cd48f0f64ce29 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -1564,11 +1564,10 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
ctx.arg.zIfuncNoplt = hasZOption(args, "ifunc-noplt");
ctx.arg.zInitfirst = hasZOption(args, "initfirst");
ctx.arg.zInterpose = hasZOption(args, "interpose");
- ctx.arg.zKeepTextSectionPrefix = getZFlag(
- args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
ctx.arg.zKeepDataSectionPrefix = getZFlag(
args, "keep-data-section-prefix", "nokeep-data-section-prefix", false);
- errs() << "ELF/Driver.cpp:1540\t" << ctx.arg.zKeepDataSectionPrefix << "\n";
+ ctx.arg.zKeepTextSectionPrefix = getZFlag(
+ args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
ctx.arg.zLrodataAfterBss =
getZFlag(args, "lrodata-after-bss", "nolrodata-after-bss", false);
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 17432e65bb1bf..f1f8f6c776c7a 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -48,9 +48,9 @@ static bool isSectionPrefix(StringRef prefix, StringRef name) {
return name.consume_front(prefix) && (name.empty() || name[0] == '.');
}
-bool hasUnlikelySuffix(StringRef name) {
- return name.ends_with(".unlikely") || name.ends_with(".unlikely.") ||
- name.ends_with("unlikely");
+static bool isSectionSuffix(StringRef suffix, StringRef name) {
+ name.consume_back(".");
+ return name.ends_with(suffix);
}
StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
@@ -110,77 +110,38 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
return ".text";
}
- if (isSectionPrefix(".data.rel.ro", s->name)) {
- // Map input sections' .rodata and rodata.hot into .rodata.hot in the
- // output. Map input sections' .rodata.unlikely into .rodata in the output.
- if (ctx.arg.zKeepDataSectionPrefix) {
- if (isSectionPrefix(".data.rel.ro.unlikely", s->name) ||
- hasUnlikelySuffix(s->name)) {
- return ".data.rel.ro.unlikely";
- }
-
- return ".data.rel.ro";
- }
- return ".data.rel.ro";
- }
-
- if (isSectionPrefix(".data", s->name)) {
- // Map input sections' .rodata and rodata.hot into .rodata.hot in the
- // output. Map input sections' .rodata.unlikely into .rodata in the output.
- if (ctx.arg.zKeepDataSectionPrefix) {
- if (isSectionPrefix(".data.unlikely", s->name) ||
- hasUnlikelySuffix(s->name)) {
- // errs() << "LinkerScript.cpp:100\t" << s->name << "\n";
- return ".data.unlikely";
- }
-
- return ".data";
- }
- return ".data";
- }
-
- if (isSectionPrefix(".rodata", s->name)) {
- // Map input sections' .rodata and rodata.hot into .rodata.hot in the
- // output. Map input sections' .rodata.unlikely into .rodata in the output.
- if (ctx.arg.zKeepDataSectionPrefix) {
- // if (isSectionPrefix(".rodata.cst", s->name)) {
- // errs() << "LinkerScript.cpp:100\t" << s->name << "\n";
- //}
- // .rodata.cst<N>.unlikely
- // .rodata.str4.16.unlikely
- if (isSectionPrefix(".rodata.unlikely", s->name) ||
- hasUnlikelySuffix(s->name)) {
- // return ".rodata.unlikely";
- return ".rodata.unlikely";
- }
- return ".rodata";
- }
- return ".rodata";
- }
-
- if (isSectionPrefix(".bss.rel.ro", s->name)) {
- return ".bss.rel.ro";
- }
+ // When zKeepDataSectionPrefix is true, keep .hot and .unlikely suffixes
+ // in data sections.
+ static constexpr StringRef dataSectionPrefixes[] = {
+ ".data.rel.ro", ".data", ".rodata", ".bss.rel.ro", ".bss",
+ };
- if (isSectionPrefix(".bss", s->name)) {
- if (ctx.arg.zKeepDataSectionPrefix) {
- if (isSectionPrefix(".bss.unlikely", s->name)) {
- // errs() << "LinkerScript.cpp:100\t" << s->name << "\n";
- return ".bss.unlikely";
+ for (auto [index, v] : llvm::enumerate(dataSectionPrefixes)) {
+ if (isSectionPrefix(v, s->name)) {
+ if (ctx.arg.zKeepDataSectionPrefix) {
+ if (isSectionPrefix(".hot", s->name.substr(v.size())))
+ return s->name.substr(0, v.size() + 4);
+ if (isSectionPrefix(".unlikely", s->name.substr(v.size())))
+ return s->name.substr(0, v.size() + 9);
+ // for .rodata, a section could be`.rodata.cst<N>.hot.` for constant
+ // pool or `rodata.str<N>.hot.` for string literals.
+ if (index == 2) {
+ if (isSectionSuffix(".hot", s->name)) {
+ return ".rodata.hot";
+ }
+ if (isSectionSuffix(".unlikely", s->name)) {
+ return ".rodata.unlikely";
+ }
+ }
}
-
- return ".bss";
+ return v;
}
- return ".bss";
}
- for (StringRef v : {".data.rel.ro", ".data", ".rodata",
- ".bss.rel.ro", ".bss", ".ldata",
- ".lrodata", ".lbss", ".gcc_except_table",
- ".init_array", ".fini_array", ".tbss",
- ".tdata", ".ARM.exidx", ".ARM.extab",
- ".ctors", ".dtors", ".sbss",
- ".sdata", ".srodata"})
+ for (StringRef v :
+ {".ldata", ".lrodata", ".lbss", ".gcc_except_table", ".init_array",
+ ".fini_array", ".tbss", ".tdata", ".ARM.exidx", ".ARM.extab", ".ctors",
+ ".dtors", ".sbss", ".sdata", ".srodata"})
if (isSectionPrefix(v, s->name))
return v;
>From 25c61499fb130bf5d8827afde108aa8a2f3952b2 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Mon, 21 Jul 2025 13:42:50 -0700
Subject: [PATCH 3/8] update code comment, and add a regression test
---
lld/ELF/Driver.cpp | 1 -
lld/ELF/LinkerScript.cpp | 7 +-
lld/ELF/Writer.cpp | 23 +++++-
lld/test/ELF/data-section-prefix.s | 127 +++++++++++++++++++++++++++++
4 files changed, 154 insertions(+), 4 deletions(-)
create mode 100644 lld/test/ELF/data-section-prefix.s
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index cd48f0f64ce29..b1b55247388a3 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -1568,7 +1568,6 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
args, "keep-data-section-prefix", "nokeep-data-section-prefix", false);
ctx.arg.zKeepTextSectionPrefix = getZFlag(
args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
-
ctx.arg.zLrodataAfterBss =
getZFlag(args, "lrodata-after-bss", "nolrodata-after-bss", false);
ctx.arg.zNoBtCfi = hasZOption(args, "nobtcfi");
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index f1f8f6c776c7a..f2b20db7b0521 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -118,12 +118,15 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
for (auto [index, v] : llvm::enumerate(dataSectionPrefixes)) {
if (isSectionPrefix(v, s->name)) {
- if (ctx.arg.zKeepDataSectionPrefix) {
+ // The .bss.rel.ro section is considered rarely accessed. So this section
+ // is not partitioned and zKeepDataSectionPrefix is not applied to
+ // make the executable simpler with fewer elf sections.
+ if (ctx.arg.zKeepDataSectionPrefix && index != 3) {
if (isSectionPrefix(".hot", s->name.substr(v.size())))
return s->name.substr(0, v.size() + 4);
if (isSectionPrefix(".unlikely", s->name.substr(v.size())))
return s->name.substr(0, v.size() + 9);
- // for .rodata, a section could be`.rodata.cst<N>.hot.` for constant
+ // For .rodata, a section could be`.rodata.cst<N>.hot.` for constant
// pool or `rodata.str<N>.hot.` for string literals.
if (index == 2) {
if (isSectionSuffix(".hot", s->name)) {
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 2cea6a44b391a..82e5ba6d9e6a8 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -555,6 +555,27 @@ template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
}
}
+// Returns true if the section is a data section that's read only and
+// relocatable per its section name.
+static bool isRelRoDataSection(Ctx &ctx, StringRef secName) {
+ // The section name should start with ".data.rel.ro".
+ if (!secName.consume_front(".data.rel.ro"))
+ return false;
+
+ // If the section name is .data.rel.ro, it is a relocatable read-only data
+ // section.
+ if (secName.empty())
+ return true;
+ // If -z keep-data-section-prefix is given, '.data.rel.ro.hot' and
+ // '.data.rel.ro.unlikely' are considered a split of '.data.rel.ro' based on
+ // hotness.
+ if (ctx.arg.zKeepDataSectionPrefix) {
+ return secName == ".hot" || secName == ".unlikely";
+ }
+
+ return false;
+}
+
// Today's loaders have a feature to make segments read-only after
// processing dynamic relocations to enhance security. PT_GNU_RELRO
// is defined for that.
@@ -631,7 +652,7 @@ static bool isRelroSection(Ctx &ctx, const OutputSection *sec) {
// magic section names.
StringRef s = sec->name;
- bool abiAgnostic = s == ".data.rel.ro" || s == ".bss.rel.ro" ||
+ bool abiAgnostic = isRelRoDataSection(ctx, s) || s == ".bss.rel.ro" ||
s == ".ctors" || s == ".dtors" || s == ".jcr" ||
s == ".eh_frame" || s == ".fini_array" ||
s == ".init_array" || s == ".preinit_array";
diff --git a/lld/test/ELF/data-section-prefix.s b/lld/test/ELF/data-section-prefix.s
new file mode 100644
index 0000000000000..5012039e438a7
--- /dev/null
+++ b/lld/test/ELF/data-section-prefix.s
@@ -0,0 +1,127 @@
+# REQUIRES: x86
+## -z keep-data-section-prefix separates static data sections with prefix
+## .<section>.hot, .<section>.unlikely in the absence of a SECTIONS command.
+
+# RUN: rm -rf %t && split-file %s %t && cd %t
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 a.s -o a.o
+
+# RUN: ld.lld a.o -o out1
+# RUN: llvm-readelf -S out1 | FileCheck --check-prefix=BASIC %s
+# RUN: ld.lld -z nokeep-text-section-prefix a.o -o out2
+# RUN: cmp out1 out2
+
+# RUN: ld.lld -z keep-data-section-prefix a.o -o out3
+# RUN: llvm-readelf -S out3 | FileCheck --check-prefix=KEEP %s
+
+## With a SECTIONS command, orphan sections are created verbatim.
+## No grouping is performed for them.
+# RUN: ld.lld -T x.lds -z keep-data-section-prefix a.o -o out4
+# RUN: llvm-readelf -S out4 | FileCheck --check-prefix=SCRIPT %s
+
+# BASIC: [Nr] Name Type Address Off Size
+# BASIC: [ 1] .text
+# BASIC-NEXT: [ 2] .data.rel.ro PROGBITS 00000000002021c9 0001c9 00000f
+# BASIC-NEXT: [ 3] .bss.rel.ro NOBITS 00000000002021d8 0001d8 000008
+# BASIC-NEXT: [ 4] .relro_padding NOBITS 00000000002021e0 0001d8 000e20
+# BASIC-NEXT: [ 5] .rodata PROGBITS 00000000002031e0 0001e0 000006
+# BASIC-NEXT: [ 6] .data PROGBITS 00000000002031e6 0001e6 000004
+# BASIC-NEXT: [ 7] .bss NOBITS 00000000002031ea 0001ea 000004
+
+# KEEP: [Nr] Name Type Address Off Size
+# KEEP: [ 1] .text
+# KEEP-NEXT: [ 2] .data.rel.ro PROGBITS 00000000002021c9 0001c9 000009
+# KEEP-NEXT: [ 3] .data.rel.ro.hot PROGBITS 00000000002021d2 0001d2 000004
+# KEEP-NEXT: [ 4] .data.rel.ro.unlikely PROGBITS 00000000002021d6 0001d6 000002
+# KEEP-NEXT: [ 5] .bss.rel.ro NOBITS 00000000002021d8 0001d8 000008
+# KEEP-NEXT: [ 6] .relro_padding NOBITS 00000000002021e0 0001d8 000e20
+# KEEP-NEXT: [ 7] .rodata PROGBITS 00000000002031e0 0001e0 000002
+# KEEP-NEXT: [ 8] .rodata.hot PROGBITS 00000000002031e2 0001e2 000002
+# KEEP-NEXT: [ 9] .rodata.unlikely PROGBITS 00000000002031e4 0001e4 000002
+# KEEP-NEXT: [10] .data PROGBITS 00000000002031e6 0001e6 000002
+# KEEP-NEXT: [11] .data.hot PROGBITS 00000000002031e8 0001e8 000001
+# KEEP-NEXT: [12] .data.unlikely PROGBITS 00000000002031e9 0001e9 000001
+# KEEP-NEXT: [13] .bss NOBITS 00000000002031ea 0001ea 000002
+# KEEP-NEXT: [14] .bss.hot NOBITS 00000000002031ec 0001ea 000001
+# KEEP-NEXT: [15] .bss.unlikely NOBITS 00000000002031ed 0001ea 000001
+
+# SCRIPT: .text
+# SCRIPT-NEXT: .rodata.i
+# SCRIPT-NEXT: .rodata.hot.j
+# SCRIPT-NEXT: .rodata.unlikely.k
+# SCRIPT-NEXT: .rodata.split.l
+# SCRIPT-NEXT: .rodata.cst32.hot.
+# SCRIPT-NEXT: .rodata.str1.1.unlikely.
+# SCRIPT-NEXT: .data.m
+# SCRIPT-NEXT: .data.hot.n
+# SCRIPT-NEXT: .data.unlikely.o
+# SCRIPT-NEXT: .data.split.p
+# SCRIPT-NEXT: .data.rel.ro.q
+# SCRIPT-NEXT: .data.rel.ro.hot.r
+# SCRIPT-NEXT: .data.rel.ro.unlikely.s
+# SCRIPT-NEXT: .data.rel.ro.split.t
+# SCRIPT-NEXT: .bss.a
+# SCRIPT-NEXT: .bss.hot.b
+# SCRIPT-NEXT: .bss.unlikely.c
+# SCRIPT-NEXT: .bss.split.d
+# SCRIPT-NEXT: .bss.rel.ro.e
+# SCRIPT-NEXT: .bss.rel.ro.hot.f
+# SCRIPT-NEXT: .bss.rel.ro.unlikely.g
+# SCRIPT-NEXT: .bss.rel.ro.split.h
+
+#--- a.s
+.globl _start
+_start:
+ ret
+
+.section .bss.a,"aw"
+ .byte 0
+.section .bss.hot.b,"aw"
+ .byte 0
+.section .bss.unlikely.c,"aw"
+ .byte 0
+.section .bss.split.d,"aw"
+ .byte 0
+
+.section .bss.rel.ro.e, "aw"
+ .space 2
+.section .bss.rel.ro.hot.f, "aw"
+ .space 2
+.section .bss.rel.ro.unlikely.g, "aw"
+ .space 2
+.section .bss.rel.ro.split.h, "aw"
+ .space 2
+
+.section .rodata.i,"aw"
+ .byte 1
+.section .rodata.hot.j,"aw"
+ .byte 2
+.section .rodata.unlikely.k,"aw"
+ .byte 3
+.section .rodata.split.l,"aw"
+ .byte 4
+.section .rodata.cst32.hot.,"aw"
+ .byte 5
+.section .rodata.str1.1.unlikely.,"aw"
+ .byte 6
+
+.section .data.m,"aw"
+ .byte 5
+.section .data.hot.n,"aw"
+ .byte 6
+.section .data.unlikely.o,"aw"
+ .byte 7
+.section .data.split.p,"aw"
+ .byte 8
+
+.section .data.rel.ro.q,"aw"
+ .quad 0
+.section .data.rel.ro.hot.r,"aw"
+ .long 255
+.section .data.rel.ro.unlikely.s,"aw"
+ .word 1
+.section .data.rel.ro.split.t,"aw"
+ .byte 0
+
+#--- x.lds
+SECTIONS {}
>From 67e44ed7a9ccd089b142bb6e52cd181ed8ed2cbb Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Mon, 21 Jul 2025 22:32:54 -0700
Subject: [PATCH 4/8] resolve comments
---
lld/ELF/LinkerScript.cpp | 6 ++++--
lld/test/ELF/data-section-prefix.s | 8 ++++----
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index f2b20db7b0521..1351e1686c3e2 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -118,10 +118,12 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
for (auto [index, v] : llvm::enumerate(dataSectionPrefixes)) {
if (isSectionPrefix(v, s->name)) {
+ if (!ctx.arg.zKeepDataSectionPrefix)
+ return v;
// The .bss.rel.ro section is considered rarely accessed. So this section
// is not partitioned and zKeepDataSectionPrefix is not applied to
// make the executable simpler with fewer elf sections.
- if (ctx.arg.zKeepDataSectionPrefix && index != 3) {
+
if (isSectionPrefix(".hot", s->name.substr(v.size())))
return s->name.substr(0, v.size() + 4);
if (isSectionPrefix(".unlikely", s->name.substr(v.size())))
@@ -136,7 +138,7 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
return ".rodata.unlikely";
}
}
- }
+
return v;
}
}
diff --git a/lld/test/ELF/data-section-prefix.s b/lld/test/ELF/data-section-prefix.s
index 5012039e438a7..a5c347ec275c6 100644
--- a/lld/test/ELF/data-section-prefix.s
+++ b/lld/test/ELF/data-section-prefix.s
@@ -83,13 +83,13 @@ _start:
.section .bss.split.d,"aw"
.byte 0
-.section .bss.rel.ro.e, "aw"
+.section .bss.rel.ro, "aw"
.space 2
-.section .bss.rel.ro.hot.f, "aw"
+.section .bss.rel.ro, "aw"
.space 2
-.section .bss.rel.ro.unlikely.g, "aw"
+.section .bss.rel.ro, "aw"
.space 2
-.section .bss.rel.ro.split.h, "aw"
+.section .bss.rel.ro, "aw"
.space 2
.section .rodata.i,"aw"
>From ed70327841c951a57b07d1a628e8c9c40d347fe8 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Wed, 23 Jul 2025 11:23:46 -0700
Subject: [PATCH 5/8] resolve comments
---
lld/ELF/LinkerScript.cpp | 46 ++++++++--------
...on-prefix.s => keep-data-section-prefix.s} | 53 +++++++++----------
2 files changed, 48 insertions(+), 51 deletions(-)
rename lld/test/ELF/{data-section-prefix.s => keep-data-section-prefix.s} (51%)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 1351e1686c3e2..e4274e95241db 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -48,9 +48,10 @@ static bool isSectionPrefix(StringRef prefix, StringRef name) {
return name.consume_front(prefix) && (name.empty() || name[0] == '.');
}
-static bool isSectionSuffix(StringRef suffix, StringRef name) {
- name.consume_back(".");
- return name.ends_with(suffix);
+// If name starts with prefix, trim the prefix and return true.
+// Otherwise, leave the name unchanged and return false.
+static bool trimSectionPrefix(StringRef prefix, StringRef &name) {
+ return name.consume_front(prefix) && (name.empty() || name[0] == '.');
}
StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
@@ -117,28 +118,27 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
};
for (auto [index, v] : llvm::enumerate(dataSectionPrefixes)) {
- if (isSectionPrefix(v, s->name)) {
+ StringRef secName = s->name;
+ if (trimSectionPrefix(v, secName)) {
if (!ctx.arg.zKeepDataSectionPrefix)
return v;
- // The .bss.rel.ro section is considered rarely accessed. So this section
- // is not partitioned and zKeepDataSectionPrefix is not applied to
- // make the executable simpler with fewer elf sections.
-
- if (isSectionPrefix(".hot", s->name.substr(v.size())))
- return s->name.substr(0, v.size() + 4);
- if (isSectionPrefix(".unlikely", s->name.substr(v.size())))
- return s->name.substr(0, v.size() + 9);
- // For .rodata, a section could be`.rodata.cst<N>.hot.` for constant
- // pool or `rodata.str<N>.hot.` for string literals.
- if (index == 2) {
- if (isSectionSuffix(".hot", s->name)) {
- return ".rodata.hot";
- }
- if (isSectionSuffix(".unlikely", s->name)) {
- return ".rodata.unlikely";
- }
- }
-
+ if (isSectionPrefix(".hot", secName))
+ return s->name.substr(0, v.size() + 4);
+ if (isSectionPrefix(".unlikely", secName))
+ return s->name.substr(0, v.size() + 9);
+ // For .rodata, a section could be`.rodata.cst<N>.hot.` for constant
+ // pool or `rodata.str<N>.hot.` for string literals.
+ if (index == 2) {
+ // The reason to specialize this path is to spell out .rodata.hot and
+ // .rodata.unlikely as string literals for StringRef lifetime
+ // considerations. We cannot use the pattern above to get substr from
+ // section names.
+ if (s->name.ends_with(".hot."))
+ return ".rodata.hot";
+
+ if (s->name.ends_with(".unlikely."))
+ return ".rodata.unlikely";
+ }
return v;
}
}
diff --git a/lld/test/ELF/data-section-prefix.s b/lld/test/ELF/keep-data-section-prefix.s
similarity index 51%
rename from lld/test/ELF/data-section-prefix.s
rename to lld/test/ELF/keep-data-section-prefix.s
index a5c347ec275c6..a33eb0c2d609f 100644
--- a/lld/test/ELF/data-section-prefix.s
+++ b/lld/test/ELF/keep-data-section-prefix.s
@@ -19,35 +19,36 @@
# RUN: ld.lld -T x.lds -z keep-data-section-prefix a.o -o out4
# RUN: llvm-readelf -S out4 | FileCheck --check-prefix=SCRIPT %s
-# BASIC: [Nr] Name Type Address Off Size
+# BASIC: [Nr] Name Type {{.*}} Size
# BASIC: [ 1] .text
-# BASIC-NEXT: [ 2] .data.rel.ro PROGBITS 00000000002021c9 0001c9 00000f
-# BASIC-NEXT: [ 3] .bss.rel.ro NOBITS 00000000002021d8 0001d8 000008
-# BASIC-NEXT: [ 4] .relro_padding NOBITS 00000000002021e0 0001d8 000e20
-# BASIC-NEXT: [ 5] .rodata PROGBITS 00000000002031e0 0001e0 000006
-# BASIC-NEXT: [ 6] .data PROGBITS 00000000002031e6 0001e6 000004
-# BASIC-NEXT: [ 7] .bss NOBITS 00000000002031ea 0001ea 000004
+# BASIC-NEXT: [ 2] .data.rel.ro PROGBITS {{.*}} 00000f
+# BASIC-NEXT: [ 3] .bss.rel.ro NOBITS {{.*}} 000008
+# BASIC-NEXT: [ 4] .relro_padding NOBITS {{.*}} 000e20
+# BASIC-NEXT: [ 5] .rodata PROGBITS {{.*}} 000006
+# BASIC-NEXT: [ 6] .data PROGBITS {{.*}} 000004
+# BASIC-NEXT: [ 7] .bss NOBITS {{.*}} 000004
-# KEEP: [Nr] Name Type Address Off Size
+# KEEP: [Nr] Name Type {{.*}} Size
# KEEP: [ 1] .text
-# KEEP-NEXT: [ 2] .data.rel.ro PROGBITS 00000000002021c9 0001c9 000009
-# KEEP-NEXT: [ 3] .data.rel.ro.hot PROGBITS 00000000002021d2 0001d2 000004
-# KEEP-NEXT: [ 4] .data.rel.ro.unlikely PROGBITS 00000000002021d6 0001d6 000002
-# KEEP-NEXT: [ 5] .bss.rel.ro NOBITS 00000000002021d8 0001d8 000008
-# KEEP-NEXT: [ 6] .relro_padding NOBITS 00000000002021e0 0001d8 000e20
-# KEEP-NEXT: [ 7] .rodata PROGBITS 00000000002031e0 0001e0 000002
-# KEEP-NEXT: [ 8] .rodata.hot PROGBITS 00000000002031e2 0001e2 000002
-# KEEP-NEXT: [ 9] .rodata.unlikely PROGBITS 00000000002031e4 0001e4 000002
-# KEEP-NEXT: [10] .data PROGBITS 00000000002031e6 0001e6 000002
-# KEEP-NEXT: [11] .data.hot PROGBITS 00000000002031e8 0001e8 000001
-# KEEP-NEXT: [12] .data.unlikely PROGBITS 00000000002031e9 0001e9 000001
-# KEEP-NEXT: [13] .bss NOBITS 00000000002031ea 0001ea 000002
-# KEEP-NEXT: [14] .bss.hot NOBITS 00000000002031ec 0001ea 000001
-# KEEP-NEXT: [15] .bss.unlikely NOBITS 00000000002031ed 0001ea 000001
+# KEEP-NEXT: [ 2] .data.rel.ro PROGBITS {{.*}} 000009
+# KEEP-NEXT: [ 3] .data.rel.ro.hot PROGBITS {{.*}} 000004
+# KEEP-NEXT: [ 4] .data.rel.ro.unlikely PROGBITS {{.*}} 000002
+# KEEP-NEXT: [ 5] .bss.rel.ro NOBITS {{.*}} 000008
+# KEEP-NEXT: [ 6] .relro_padding NOBITS {{.*}} 000e20
+# KEEP-NEXT: [ 7] .rodata PROGBITS {{.*}} 000002
+# KEEP-NEXT: [ 8] .rodata.hot PROGBITS {{.*}} 000002
+# KEEP-NEXT: [ 9] .rodata.unlikely PROGBITS {{.*}} 000002
+# KEEP-NEXT: [10] .data PROGBITS {{.*}} 000002
+# KEEP-NEXT: [11] .data.hot PROGBITS {{.*}} 000001
+# KEEP-NEXT: [12] .data.unlikely PROGBITS {{.*}} 000001
+# KEEP-NEXT: [13] .bss NOBITS {{.*}} 000002
+# KEEP-NEXT: [14] .bss.hot NOBITS {{.*}} 000001
+# KEEP-NEXT: [15] .bss.unlikely NOBITS {{.*}} 000001
# SCRIPT: .text
+# SCRIPT-NEXT: .bss.rel.ro
# SCRIPT-NEXT: .rodata.i
-# SCRIPT-NEXT: .rodata.hot.j
+# SCRIPT-NEXT: .rodata.hot.
# SCRIPT-NEXT: .rodata.unlikely.k
# SCRIPT-NEXT: .rodata.split.l
# SCRIPT-NEXT: .rodata.cst32.hot.
@@ -64,10 +65,6 @@
# SCRIPT-NEXT: .bss.hot.b
# SCRIPT-NEXT: .bss.unlikely.c
# SCRIPT-NEXT: .bss.split.d
-# SCRIPT-NEXT: .bss.rel.ro.e
-# SCRIPT-NEXT: .bss.rel.ro.hot.f
-# SCRIPT-NEXT: .bss.rel.ro.unlikely.g
-# SCRIPT-NEXT: .bss.rel.ro.split.h
#--- a.s
.globl _start
@@ -94,7 +91,7 @@ _start:
.section .rodata.i,"aw"
.byte 1
-.section .rodata.hot.j,"aw"
+.section .rodata.hot.,"aw"
.byte 2
.section .rodata.unlikely.k,"aw"
.byte 3
>From b66eceebbf47540539f9aa9b4f4d544b0bfed897 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Wed, 23 Jul 2025 12:27:40 -0700
Subject: [PATCH 6/8] use {{.*}} to omit irrelevant columns in the test case
---
lld/test/ELF/keep-data-section-prefix.s | 36 ++++++++++++-------------
1 file changed, 18 insertions(+), 18 deletions(-)
diff --git a/lld/test/ELF/keep-data-section-prefix.s b/lld/test/ELF/keep-data-section-prefix.s
index 0521ff0b7519a..a44be263e821f 100644
--- a/lld/test/ELF/keep-data-section-prefix.s
+++ b/lld/test/ELF/keep-data-section-prefix.s
@@ -38,12 +38,12 @@
## The first RW PT_LOAD segment has FileSiz 0x126f (0x1000 + 0x200 + 0x60 + 0xf),
## and its p_offset p_vaddr p_paddr p_filesz should match PT_GNU_RELRO.
-# Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
-# SEG: LOAD 0x0001c8 0x00000000002011c8 0x00000000002011c8 0x000001 0x000001 R E 0x1000
-# SEG-NEXT: LOAD 0x0001c9 0x00000000002021c9 0x00000000002021c9 0x00126f 0x001e37 RW 0x1000
-# SEG-NEXT: LOAD 0x001438 0x0000000000204438 0x0000000000204438 0x000001 0x000002 RW 0x1000
-# SEG-NEXT: GNU_RELRO 0x0001c9 0x00000000002021c9 0x00000000002021c9 0x00126f 0x001e37 R 0x1
-# SEG-NEXT: GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x0
+# Type {{.*}} FileSiz MemSiz Flg
+# SEG: LOAD {{.*}} 0x000001 0x000001 R E
+# SEG-NEXT: LOAD {{.*}} 0x00126f 0x001e37 RW
+# SEG-NEXT: LOAD {{.*}} 0x000001 0x000002 RW
+# SEG-NEXT: GNU_RELRO {{.*}} 0x00126f 0x001e37 R
+# SEG-NEXT: GNU_STACK {{.*}} 0x000000 0x000000 RW
## Input to output mapping per linker script
## .data.rel.ro.split -> .data.rel.ro
@@ -54,13 +54,13 @@
# LS-NEXT: .data.rel.ro.hot .data.rel.ro .data.rel.ro.unlikely .relro_padding
# LS-NEXT: .data .bss
-# [Nr] Name Type Address Off Size
-# CHECK-LS: .data.rel.ro.hot PROGBITS 00000000002021c9 0001c9 00000f
-# CHECK-LS-NEXT: .data.rel.ro PROGBITS 00000000002021d8 0001d8 000260
-# CHECK-LS-NEXT: .data.rel.ro.unlikely PROGBITS 0000000000202438 000438 001000
-# CHECK-LS-NEXT: .relro_padding NOBITS 0000000000203438 001438 000bc8
-# CHECK-LS-NEXT: .data PROGBITS 0000000000204438 001438 000001
-# CHECK-LS-NEXT: .bss NOBITS 0000000000204439 001439 000001
+# [Nr] Name Type {{.*}} Size
+# CHECK-LS: .data.rel.ro.hot PROGBITS {{.*}} 00000f
+# CHECK-LS-NEXT: .data.rel.ro PROGBITS {{.*}} 000260
+# CHECK-LS-NEXT: .data.rel.ro.unlikely PROGBITS {{.*}} 001000
+# CHECK-LS-NEXT: .relro_padding NOBITS {{.*}} 000bc8
+# CHECK-LS-NEXT: .data PROGBITS {{.*}} 000001
+# CHECK-LS-NEXT: .bss NOBITS {{.*}} 000001
## Linker script is not provided to map data sections.
## So all input sections with prefix .data.rel.ro will map to .data.rel.ro in the output.
@@ -68,11 +68,11 @@
# PRE-NEXT: .data.rel.ro .relro_padding
# PRE-NEXT: .data .bss
-# [Nr] Name Type Address Off Size
-# CHECK-PRE: .data.rel.ro PROGBITS 00000000002021c9 0001c9 00126f
-# CHECK-PRE-NEXT: .relro_padding NOBITS 0000000000203438 001438 000bc8
-# CHECK-PRE-NEXT: .data PROGBITS 0000000000204438 001438 000001
-# CHECK-PRE-NEXT: .bss NOBITS 0000000000204439 001439 000001
+# [Nr] Name Type {{.*}} Size
+# CHECK-PRE: .data.rel.ro PROGBITS {{.*}} 00126f
+# CHECK-PRE-NEXT: .relro_padding NOBITS {{.*}} 000bc8
+# CHECK-PRE-NEXT: .data PROGBITS {{.*}} 000001
+# CHECK-PRE-NEXT: .bss NOBITS {{.*}} 000001
# BASIC: [Nr] Name Type {{.*}} Size
# BASIC: [ 1] .text
>From 5dbe4df4a8cbcfcd5b5d702a54c315ed334743cb Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Sat, 26 Jul 2025 19:28:46 -0700
Subject: [PATCH 7/8] resolve comment
---
lld/ELF/LinkerScript.cpp | 52 ++++++++++++-------------
lld/test/ELF/keep-data-section-prefix.s | 14 ++-----
2 files changed, 30 insertions(+), 36 deletions(-)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index c0f524eda2c33..2991b03d2ef2b 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -46,12 +46,6 @@ static bool isSectionPrefix(StringRef prefix, StringRef name) {
return name.consume_front(prefix) && (name.empty() || name[0] == '.');
}
-// If name starts with prefix, trim the prefix and return true.
-// Otherwise, leave the name unchanged and return false.
-static bool trimSectionPrefix(StringRef prefix, StringRef &name) {
- return name.consume_front(prefix) && (name.empty() || name[0] == '.');
-}
-
StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
// This is for --emit-relocs and -r. If .text.foo is emitted as .text.bar, we
// want to emit .rela.text.foo as .rela.text.bar for consistency (this is not
@@ -117,28 +111,34 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
for (auto [index, v] : llvm::enumerate(dataSectionPrefixes)) {
StringRef secName = s->name;
- if (trimSectionPrefix(v, secName)) {
- if (!ctx.arg.zKeepDataSectionPrefix)
- return v;
- if (isSectionPrefix(".hot", secName))
- return s->name.substr(0, v.size() + 4);
- if (isSectionPrefix(".unlikely", secName))
- return s->name.substr(0, v.size() + 9);
- // For .rodata, a section could be`.rodata.cst<N>.hot.` for constant
- // pool or `rodata.str<N>.hot.` for string literals.
- if (index == 2) {
- // The reason to specialize this path is to spell out .rodata.hot and
- // .rodata.unlikely as string literals for StringRef lifetime
- // considerations. We cannot use the pattern above to get substr from
- // section names.
- if (s->name.ends_with(".hot."))
- return ".rodata.hot";
-
- if (s->name.ends_with(".unlikely."))
- return ".rodata.unlikely";
- }
+ if (!secName.consume_front(v))
+ continue;
+ if (!secName.empty() && secName[0] != '.') {
+ continue;
+ }
+
+ // The section name starts with 'v', and the remaining string is either
+ // empty or starts with a '.' character. If keep-data-section-prefix is
+ // false, map s to output section with name 'v'.
+ if (!ctx.arg.zKeepDataSectionPrefix)
return v;
+ // Preserve .hot or .unlikely suffixes in data sections with
+ // keep-data-section-prefix=true.
+ if (isSectionPrefix(".hot", secName))
+ return s->name.substr(0, v.size() + 4);
+ if (isSectionPrefix(".unlikely", secName))
+ return s->name.substr(0, v.size() + 9);
+ if (index == 2) {
+ // Place input .rodata.str<N>.hot. or .rodata.cst<N>.hot. into the
+ // .rodata.hot section.
+ if (s->name.ends_with(".hot."))
+ return ".rodata.hot";
+ // Place input .rodata.str<N>.hot. or .rodata.cst<N>.unlikely. into the
+ // .rodata.unlikely section.
+ if (s->name.ends_with(".unlikely."))
+ return ".rodata.unlikely";
}
+ return v;
}
for (StringRef v :
diff --git a/lld/test/ELF/keep-data-section-prefix.s b/lld/test/ELF/keep-data-section-prefix.s
index a44be263e821f..a539cd66b9205 100644
--- a/lld/test/ELF/keep-data-section-prefix.s
+++ b/lld/test/ELF/keep-data-section-prefix.s
@@ -77,8 +77,8 @@
# BASIC: [Nr] Name Type {{.*}} Size
# BASIC: [ 1] .text
# BASIC-NEXT: [ 2] .data.rel.ro PROGBITS {{.*}} 00000f
-# BASIC-NEXT: [ 3] .bss.rel.ro NOBITS {{.*}} 000008
-# BASIC-NEXT: [ 4] .relro_padding NOBITS {{.*}} 000e20
+# BASIC-NEXT: [ 3] .bss.rel.ro NOBITS {{.*}} 000002
+# BASIC-NEXT: [ 4] .relro_padding NOBITS {{.*}} 000e26
# BASIC-NEXT: [ 5] .rodata PROGBITS {{.*}} 000006
# BASIC-NEXT: [ 6] .data PROGBITS {{.*}} 000004
# BASIC-NEXT: [ 7] .bss NOBITS {{.*}} 000004
@@ -88,8 +88,8 @@
# KEEP-NEXT: [ 2] .data.rel.ro PROGBITS {{.*}} 000009
# KEEP-NEXT: [ 3] .data.rel.ro.hot PROGBITS {{.*}} 000004
# KEEP-NEXT: [ 4] .data.rel.ro.unlikely PROGBITS {{.*}} 000002
-# KEEP-NEXT: [ 5] .bss.rel.ro NOBITS {{.*}} 000008
-# KEEP-NEXT: [ 6] .relro_padding NOBITS {{.*}} 000e20
+# KEEP-NEXT: [ 5] .bss.rel.ro NOBITS {{.*}} 000002
+# KEEP-NEXT: [ 6] .relro_padding NOBITS {{.*}} 000e26
# KEEP-NEXT: [ 7] .rodata PROGBITS {{.*}} 000002
# KEEP-NEXT: [ 8] .rodata.hot PROGBITS {{.*}} 000002
# KEEP-NEXT: [ 9] .rodata.unlikely PROGBITS {{.*}} 000002
@@ -165,12 +165,6 @@ _start:
.section .bss.split.d,"aw"
.byte 0
-.section .bss.rel.ro, "aw"
- .space 2
-.section .bss.rel.ro, "aw"
- .space 2
-.section .bss.rel.ro, "aw"
- .space 2
.section .bss.rel.ro, "aw"
.space 2
>From 28b26f8643454cb891c034dd6385e6eca383b92d Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Mon, 4 Aug 2025 14:24:54 -0700
Subject: [PATCH 8/8] drop braces for single-line if
---
lld/ELF/LinkerScript.cpp | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 2991b03d2ef2b..9652d39f72616 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -113,9 +113,8 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
StringRef secName = s->name;
if (!secName.consume_front(v))
continue;
- if (!secName.empty() && secName[0] != '.') {
+ if (!secName.empty() && secName[0] != '.')
continue;
- }
// The section name starts with 'v', and the remaining string is either
// empty or starts with a '.' character. If keep-data-section-prefix is
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