[llvm-bugs] [Bug 39711] New: Broken PLT in statically linked binary with -z now -z retpolineplt

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Mon Nov 19 12:17:16 PST 2018


            Bug ID: 39711
           Summary: Broken PLT in statically linked binary with -z now -z
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: FreeBSD
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: ELF
          Assignee: unassignedbugs at nondot.org
          Reporter: emaste at freebsd.org
                CC: llvm-bugs at lists.llvm.org, peter.smith at linaro.org

Hello world test code:
% cat hello.c
#include <stdio.h>
int main(int argc, char *argv[]) { printf("Hi\n"); }

lld version:
% ld.lld --version
LLD 6.0.1 (FreeBSD 335540-1200005) (compatible with GNU linkers)

Build test application:
% LLD_REPRODUCE=hello.tar cc -g -static -Wl,-zretpolineplt,-znow hello.c -o

Application segfaults:
% ./hello.static-retpoline-now
zsh: illegal hardware instruction (core dumped)  ./hello.static-retpoline-now

We have a PLT entry that jumps to an invalid location:
% objdump -S -section=.plt hello.static-retpoline-now

hello.static-retpoline-now:     file format ELF64-x86-64

Disassembly of section .plt:
  2a0890:       4c 8b 1d a9 5f 00 00    movq    24489(%rip), %r11
  2a0897:       e9 d4 ff ff ff  jmp     -44 <_init+0x8>
  2a089c:       cc      int3
  2a089d:       cc      int3
  2a089e:       cc      int3
  2a089f:       cc      int3

Note that there is a .plt entry here, but no PLT header.

Reproducer: https://people.freebsd.org/~emaste/lld/hello.tar.xz
See also FreeBSD PR 233336 https://bugs.freebsd.org/233336

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