[lld] r332332 - [ELF] Implement --keep-unique option
Peter Smith via llvm-commits
llvm-commits at lists.llvm.org
Tue May 15 01:57:21 PDT 2018
Author: psmith
Date: Tue May 15 01:57:21 2018
New Revision: 332332
URL: http://llvm.org/viewvc/llvm-project?rev=332332&view=rev
Log:
[ELF] Implement --keep-unique option
The --keep-unique <symbol> option is taken from gold. The intention is that
<symbol> will be prevented from being folded by ICF. Although not
specifically mentioned in the documentation <symbol> only matches
global symbols, with a warning if the symbol is not found.
The implementation finds the Section defining <symbol> and removes it from
the set of sections considered for ICF.
Differential Revision: https://reviews.llvm.org/D46755
Added:
lld/trunk/test/ELF/icf-keep-unique.s
Modified:
lld/trunk/ELF/Driver.cpp
lld/trunk/ELF/ICF.cpp
lld/trunk/ELF/InputSection.h
lld/trunk/ELF/Options.td
Modified: lld/trunk/ELF/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Driver.cpp?rev=332332&r1=332331&r2=332332&view=diff
==============================================================================
--- lld/trunk/ELF/Driver.cpp (original)
+++ lld/trunk/ELF/Driver.cpp Tue May 15 01:57:21 2018
@@ -1163,6 +1163,18 @@ template <class ELFT> static void demote
}
}
+// Record sections that define symbols mentioned in --keep-unique <symbol>
+// these sections are inelligible for ICF.
+static void findKeepUniqueSections(opt::InputArgList &Args) {
+ for (auto *Arg : Args.filtered(OPT_keep_unique)) {
+ StringRef Name = Arg->getValue();
+ if (auto *Sym = dyn_cast_or_null<Defined>(Symtab->find(Name)))
+ Sym->Section->KeepUnique = true;
+ else
+ warn("could not find symbol " + Name + " to keep unique");
+ }
+}
+
// Do actual linking. Note that when this function is called,
// all linker scripts have already been parsed.
template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
@@ -1335,8 +1347,10 @@ template <class ELFT> void LinkerDriver:
markLive<ELFT>();
demoteSymbols<ELFT>();
mergeSections();
- if (Config->ICF)
+ if (Config->ICF) {
+ findKeepUniqueSections(Args);
doIcf<ELFT>();
+ }
// Read the callgraph now that we know what was gced or icfed
if (auto *Arg = Args.getLastArg(OPT_call_graph_ordering_file))
Modified: lld/trunk/ELF/ICF.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/ICF.cpp?rev=332332&r1=332331&r2=332332&view=diff
==============================================================================
--- lld/trunk/ELF/ICF.cpp (original)
+++ lld/trunk/ELF/ICF.cpp Tue May 15 01:57:21 2018
@@ -162,7 +162,8 @@ template <class ELFT> static uint32_t ge
// Returns true if section S is subject of ICF.
static bool isEligible(InputSection *S) {
- if (!S->Live || !(S->Flags & SHF_ALLOC) || (S->Flags & SHF_WRITE))
+ if (!S->Live || S->KeepUnique || !(S->Flags & SHF_ALLOC) ||
+ (S->Flags & SHF_WRITE))
return false;
// Don't merge read only data sections unless
Modified: lld/trunk/ELF/InputSection.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.h?rev=332332&r1=332331&r2=332332&view=diff
==============================================================================
--- lld/trunk/ELF/InputSection.h (original)
+++ lld/trunk/ELF/InputSection.h Tue May 15 01:57:21 2018
@@ -61,6 +61,9 @@ public:
unsigned Bss : 1;
+ // Set for sections that should not be folded by ICF.
+ unsigned KeepUnique : 1;
+
// These corresponds to the fields in Elf_Shdr.
uint32_t Alignment;
uint64_t Flags;
@@ -85,8 +88,8 @@ protected:
uint64_t Entsize, uint64_t Alignment, uint32_t Type,
uint32_t Info, uint32_t Link)
: Name(Name), Repl(this), SectionKind(SectionKind), Live(false),
- Bss(false), Alignment(Alignment), Flags(Flags), Entsize(Entsize),
- Type(Type), Link(Link), Info(Info) {}
+ Bss(false), KeepUnique(false), Alignment(Alignment), Flags(Flags),
+ Entsize(Entsize), Type(Type), Link(Link), Info(Info) {}
};
// This corresponds to a section of an input file.
Modified: lld/trunk/ELF/Options.td
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Options.td?rev=332332&r1=332331&r2=332332&view=diff
==============================================================================
--- lld/trunk/ELF/Options.td (original)
+++ lld/trunk/ELF/Options.td Tue May 15 01:57:21 2018
@@ -192,6 +192,8 @@ defm init: Eq<"init">, HelpText<"Specify
defm just_symbols: Eq<"just-symbols">, HelpText<"Just link symbols">;
+defm keep_unique: Eq<"keep-unique">, HelpText<"Do not fold this symbol during ICF">;
+
defm library: Eq<"library">, HelpText<"Root name of library to use">,
MetaVarName<"<libName>">;
Added: lld/trunk/test/ELF/icf-keep-unique.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/icf-keep-unique.s?rev=332332&view=auto
==============================================================================
--- lld/trunk/test/ELF/icf-keep-unique.s (added)
+++ lld/trunk/test/ELF/icf-keep-unique.s Tue May 15 01:57:21 2018
@@ -0,0 +1,43 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %t2 --icf=all --print-icf-sections | FileCheck %s
+# RUN: ld.lld %t -o %t2 --keep-unique f2 --keep-unique f4 --keep-unique f5 --icf=all --print-icf-sections 2>&1 | FileCheck %s -check-prefix=CHECK-KEEP
+
+// Base case, expect only .text.f1 to be kept
+// CHECK: selected section {{.*}}:(.text.f1)
+// CHECK-NEXT: removing identical section {{.*}}:(.text.f2)
+// CHECK-NEXT: removing identical section {{.*}}:(.text.f3)
+// CHECK-NEXT: removing identical section {{.*}}:(.text.f4)
+// CHECK-NEXT: removing identical section {{.*}}:(.text.f5)
+
+// With --keep-unique f2, f4 and f5 we expect only f3 and f5 to be removed.
+// f5 is not matched by --keep-unique as it is a local symbol.
+// CHECK-KEEP: warning: could not find symbol f5 to keep unique
+// CHECK-KEEP: selected section {{.*}}:(.text.f1)
+// CHECK-KEEP-NEXT: removing identical section {{.*}}:(.text.f3)
+// CHECK-KEEP-NEXT: removing identical section {{.*}}:(.text.f5)
+ .globl _start, f1, f2, f3, f4
+_start:
+ ret
+
+ .section .text.f1, "ax"
+f1:
+ nop
+
+ .section .text.f2, "ax"
+f2:
+ nop
+
+.section .text.f3, "ax"
+f3:
+ nop
+
+.section .text.f4, "ax"
+f4:
+ nop
+
+# f5 is local, not found by --keep-unique f5
+.section .text.f5, "ax"
+f5:
+ nop
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