[llvm-bugs] [Bug 48357] New: Crash when building arm64 Linux kernel with --emit-relocs

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48357

            Bug ID: 48357
           Summary: Crash when building arm64 Linux kernel with
                    --emit-relocs
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: ELF
          Assignee: unassignedbugs at nondot.org
          Reporter: david.brazdil at gmail.com
                CC: llvm-bugs at lists.llvm.org, smithp352 at googlemail.com

Hi,

I've been experimenting with relocs in the arm64 Linux kernel and managed to
get an LLD crash.
Checked llvm-project ToT (commit e0bf2349303f6b40e3ddd5377ea08a5c0867ece4) and
it still happens there.

>From quick debugging, it is a null-pointer `first` in
lld/ELF/OutputSections.cpp, OutputSection::finalize():

```
  if (!config->copyRelocs || (type != SHT_RELA && type != SHT_REL))
    return;

  if (isa<SyntheticSection>(first))   // <<<< HERE
    return;

  link = in.symTab->getParent()->sectionIndex;

```

The kernel is v5.10-rc1 built with `CONFIG_RELOCATABLE=n` and the following
diff:

```
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 5789c2d18d43..aa68f6b6524a 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -18,6 +18,8 @@ ifeq ($(CONFIG_RELOCATABLE), y)
 # with the relocation offsets always being zero.
 LDFLAGS_vmlinux                += -shared -Bsymbolic -z notext \
                        $(call ld-option, --no-apply-dynamic-relocs)
+else
+LDFLAGS_vmlinux                += --emit-relocs
 endif

 ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
```


The crash:

+ ld.lld -EL -maarch64elf --no-undefined -X -z norelro --emit-relocs
--fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o
.tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive
arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a
kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a
security/built-in.a crypto/built-in.a block/built-in.a
arch/arm64/lib/built-in.a lib/built-in.a arch/arm64/lib/lib.a lib/lib.a
drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a
--no-whole-archive --start-group ./drivers/firmware/efi/libstub/lib.a
--end-group

PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash
backtrace.
Stack dump:
0.      Program arguments: ld.lld -EL -maarch64elf --no-undefined -X -z norelro
--emit-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1
--strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds
--whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a
arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a
fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a
block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a arch/arm64/lib/lib.a
lib/lib.a drivers/built-in.a sound/built-in.a net/built-in.a virt/
built-in.a --no-whole-archive --start-group
./drivers/firmware/efi/libstub/lib.a --end-group
 #0 0x000000000162fa63 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x162fa63)
 #1 0x000000000162d9be llvm::sys::RunSignalHandlers()
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x162d9be)
 #2 0x00000000016301f5 SignalHandler(int)
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x16301f5)
 #3 0x00007fc459efa140 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x14140)
 #4 0x00000000017b8e7e lld::elf::OutputSection::finalize()
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x17b8e7e)
 #5 0x00000000018eca68 (anonymous
namespace)::Writer<llvm::object::ELFType<(llvm::support::endianness)1, true>
>::finalizeSections()
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x18eca68)
 #6 0x00000000018b868b void
lld::elf::writeResult<llvm::object::ELFType<(llvm::support::endianness)1, true>
>() (/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x18b868b)
 #7 0x000000000170fad6 void
lld::elf::LinkerDriver::link<llvm::object::ELFType<(llvm::support::endianness)1,
true> >(llvm::opt::InputArgList&)
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x170fad6)
 #8 0x00000000017008e1 lld::elf::LinkerDriver::main(llvm::ArrayRef<char
const*>)
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x17008e1)
 #9 0x00000000016fe15f lld::elf::link(llvm::ArrayRef<char const*>, bool,
llvm::raw_ostream&, llvm::raw_ostream&)
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x16fe15f)
#10 0x000000000159be55 lldMain(int, char const**, llvm::raw_ostream&,
llvm::raw_ostream&, bool)
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x159be55)
#11 0x000000000159b6c0 main
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x159b6c0)
#12 0x00007fc4599eccca __libc_start_main ./csu/../csu/libc-start.c:308:16
#13 0x000000000159b3ba _start
(/usr/local/google/home/dbrazdil/dev/tc-build/install/bin/lld+0x159b3ba)
../scripts/link-vmlinux.sh: line 89: 43038 Segmentation fault      ${LD}
${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux} ${strip_debug#-Wl,} -o ${output} -T ${lds}
${objects}

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