[ELF] Write IPLT header in -static -z retpolineplt mode
Summary:
This fixes PR39711: -static -z retpolineplt does not produce retpoline PLT header.
-z now is not relevant.
Statically linked executable does not have PLT, but may have IPLT with no header. When -z retpolineplt is specified, however, the repoline PLT header should still be emitted.
I've checked that this fixes the FreeBSD reproduce in PR39711 and a Linux program statically linked against glibc. The programm print "Hi" rather than SIGILL/SIGSEGV.
getPltEntryOffset may look dirty after this patch, but it can be cleaned up later.
Another possible improvement is that when there are non-preemptible IFUNC symbols (rare case, e.g. -Bsymbolic), both In.Plt and In.Iplt can be non-empty and we'll emit the retpoline PLT header twice.
Reviewers: espindola, emaste, chandlerc, ruiu
Reviewed By: emaste
Subscribers: emaste, arichardson, krytarowski, llvm-commits
Differential Revision: https://reviews.llvm.org/D54782
git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@347404 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/ELF/Symbols.cpp b/ELF/Symbols.cpp
index 2ff2edf..80a3b46 100644
--- a/ELF/Symbols.cpp
+++ b/ELF/Symbols.cpp
@@ -144,8 +144,11 @@
}
uint64_t Symbol::getPltVA() const {
- if (this->IsInIplt)
+ if (this->IsInIplt) {
+ if (Config->ZRetpolineplt)
+ return In.Iplt->getVA() + Target->getPltEntryOffset(PltIndex);
return In.Iplt->getVA() + PltIndex * Target->PltEntrySize;
+ }
return In.Plt->getVA() + Target->getPltEntryOffset(PltIndex);
}
diff --git a/ELF/SyntheticSections.cpp b/ELF/SyntheticSections.cpp
index 97fd839..ab71e1b 100644
--- a/ELF/SyntheticSections.cpp
+++ b/ELF/SyntheticSections.cpp
@@ -2280,7 +2280,8 @@
PltSection::PltSection(bool IsIplt)
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16,
Config->EMachine == EM_PPC64 ? ".glink" : ".plt"),
- HeaderSize(IsIplt ? 0 : Target->PltHeaderSize), IsIplt(IsIplt) {
+ HeaderSize(!IsIplt || Config->ZRetpolineplt ? Target->PltHeaderSize : 0),
+ IsIplt(IsIplt) {
// The PLT needs to be writable on SPARC as the dynamic linker will
// modify the instructions in the PLT entries.
if (Config->EMachine == EM_SPARCV9)
@@ -2288,9 +2289,9 @@
}
void PltSection::writeTo(uint8_t *Buf) {
- // At beginning of PLT but not the IPLT, we have code to call the dynamic
+ // At beginning of PLT or retpoline IPLT, we have code to call the dynamic
// linker to resolve dynsyms at runtime. Write such code.
- if (!IsIplt)
+ if (HeaderSize > 0)
Target->writePltHeader(Buf);
size_t Off = HeaderSize;
// The IPlt is immediately after the Plt, account for this in RelOff
diff --git a/test/ELF/x86-64-retpoline-znow-static-iplt.s b/test/ELF/x86-64-retpoline-znow-static-iplt.s
new file mode 100644
index 0000000..0321f6e
--- /dev/null
+++ b/test/ELF/x86-64-retpoline-znow-static-iplt.s
@@ -0,0 +1,26 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld -z retpolineplt -z now %t.o -o %t
+# RUN: llvm-objdump -d -no-show-raw-insn %t | FileCheck %s
+
+#0x201001+5 + 42 = 0x201030 (foo@plt)
+# CHECK: _start:
+# CHECK-NEXT: 201001: callq 42
+
+#Static IPLT header due to -z retpolineplt
+# CHECK: {{^}}.plt:
+# CHECK-NEXT: 201010: callq 11 <.plt+0x10>
+# CHECK-NEXT: 201015: pause
+# CHECK-NEXT: 201017: lfence
+#foo@plt
+# CHECK: 201030: movq 4041(%rip), %r11
+# CHECK-NEXT: 201037: jmp -44 <.plt>
+
+.type foo STT_GNU_IFUNC
+.globl foo
+foo:
+ ret
+
+.globl _start
+_start:
+ call foo
