commit 2ef424d3710cf6676e3756231cd967f4a5abfa45
author Fangrui Song <i@maskray.me> Fri Nov 19 10:50:53 2021 -0800
committer Copybara-Service <copybara-worker@google.com> Fri Nov 19 10:56:39 2021 -0800
tree c291a04f06715e45811127016df940d21cb537af
parent 3a21482a72785709d411d558650a74074c8292b4

[ELF] Support discarding .got.plt

Fix a null pointer dereference when .got.plt is discarded.

This also adds a test for discarding `.plt`.

Reviewed By: ikudrin

Differential Revision: https://reviews.llvm.org/D114180

GitOrigin-RevId: 2997441b85c0ec94425e83316d7e63c32d8c5770

ELF/SyntheticSections.cpp

diff --git a/ELF/SyntheticSections.cpp b/ELF/SyntheticSections.cpp
index 1c1720d..f1594eb 100644
--- a/ELF/SyntheticSections.cpp
+++ b/ELF/SyntheticSections.cpp
@@ -1668,11 +1668,11 @@
   else
     getParent()->link = 0;
 
-  if (in.relaPlt == this) {
+  if (in.relaPlt == this && in.gotPlt->getParent()) {
     getParent()->flags |= ELF::SHF_INFO_LINK;
     getParent()->info = in.gotPlt->getParent()->sectionIndex;
   }
-  if (in.relaIplt == this) {
+  if (in.relaIplt == this && in.igotPlt->getParent()) {
     getParent()->flags |= ELF::SHF_INFO_LINK;
     getParent()->info = in.igotPlt->getParent()->sectionIndex;
   }

test/ELF/linkerscript/discard-plt.s

diff --git a/test/ELF/linkerscript/discard-plt.s b/test/ELF/linkerscript/discard-plt.s
new file mode 100644
index 0000000..eef04ea
--- /dev/null
+++ b/test/ELF/linkerscript/discard-plt.s
@@ -0,0 +1,37 @@
+# REQUIRES: x86
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+
+## Discard .plt, .iplt, and .got.plt
+# RUN: ld.lld -shared -T %t/t %t/a.o -o %t/a
+# RUN: llvm-readelf -S -d %t/a > %t/readelf.txt
+# RUN: FileCheck %s --input-file %t/readelf.txt
+# RUN: FileCheck %s --input-file %t/readelf.txt --check-prefix=NEG
+
+# CHECK:      [Nr] Name      Type     Address  Off      Size   ES Flg Lk Inf Al
+# CHECK:      ] .rela.plt RELA     [[#%x,]] [[#%x,]] 000018 18   A  1   0  8
+
+# CHECK:      (PLTGOT)  0x0
+# CHECK:      (PLTREL)  RELA
+
+# NEG-NOT: ] .plt
+# NEG-NOT: ] .iplt
+# NEG-NOT: ] .got.plt
+
+#--- a.s
+  call foo
+  call ifunc
+
+.type ifunc, @gnu_indirect_function
+.hidden ifunc
+ifunc:
+  ret
+
+.data
+.quad ifunc
+
+#--- t
+SECTIONS {
+  .text : { *(.text) }
+  /DISCARD/ : { *(.plt .iplt .got.plt) }
+}