[PATCH] D59780: Support Intel Control-flow Enforcement Technology

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In D59780#1778882 <https://reviews.llvm.org/D59780#1778882>, @tstellar wrote:

> In D59780#1778863 <https://reviews.llvm.org/D59780#1778863>, @ruiu wrote:
>
> > Hmm, I'm sorry but I'm confused. IIRC I had a discussion in the LLVM dev meeting that we were going to submit a change with a single PLT scheme rather than IPLT, so when I said that I'm going to submit a patch, I meant that I'm going to submit a patch for the 1PLT scheme rather than the 2PLT scheme. But this is for the 2PLT scheme. This is not something I want.
>
>
> What was the decision that was made at the developer meeting?  Will lld support the 2PLT scheme defined in the psABI?


(Personally, I am still unhappy with the .plt.sec scheme.  I think I prefer a 1PLT scheme like AArch64's Branch Target Indicators (BTI) and Pointer Authentication Code (PAC).) But I thought @ruiu accepted the fait accompli because there had been very strong objection to diverge from what GNU ld does. https://groups.google.com/forum/#!topic/x86-64-abi/sQcX3__r4c0

`objdump -d` (built from binutils-gdb HEAD) still does not work with lld produced binaries.

  % objdump -d a.bfd  # -z ibt
  Disassembly of section .plt:
  
  0000000000001020 <.plt>:
      1020:       ff 35 e2 2f 00 00       pushq  0x2fe2(%rip)        # 4008 <_GLOBAL_OFFSET_TABLE_+0x8>
      1026:       f2 ff 25 e3 2f 00 00    bnd jmpq *0x2fe3(%rip)        # 4010 <_GLOBAL_OFFSET_TABLE_+0x10>
      102d:       0f 1f 00                nopl   (%rax)
      1030:       f3 0f 1e fa             endbr64 
      1034:       68 00 00 00 00          pushq  $0x0
      1039:       f2 e9 e1 ff ff ff       bnd jmpq 1020 <.plt>
      103f:       90                      nop
      1040:       f3 0f 1e fa             endbr64 
      1044:       68 01 00 00 00          pushq  $0x1
      1049:       f2 e9 d1 ff ff ff       bnd jmpq 1020 <.plt>
      104f:       90                      nop
  Disassembly of section .plt.got:
  
  0000000000001050 <__cxa_finalize at plt>:
      1050:       f3 0f 1e fa             endbr64 
      1054:       f2 ff 25 9d 2f 00 00    bnd jmpq *0x2f9d(%rip)        # 3ff8 <__cxa_finalize at GLIBC_2.2.5>
      105b:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
  
  Disassembly of section .plt.sec:
  
  0000000000001060 <puts at plt>:
      1060:       f3 0f 1e fa             endbr64 
      1064:       f2 ff 25 ad 2f 00 00    bnd jmpq *0x2fad(%rip)        # 4018 <puts at GLIBC_2.2.5>
      106b:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
  
  0000000000001070 <exit at plt>:
      1070:       f3 0f 1e fa             endbr64 
      1074:       f2 ff 25 a5 2f 00 00    bnd jmpq *0x2fa5(%rip)        # 4020 <exit at GLIBC_2.2.5>
      107b:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)



  % objdump -d a.lld  # --require-cet (actually my patched version, which behaves like AArch64's --force-bti
  ...
  Disassembly of section .plt:
  
  00000000000018c0 <.plt>:
      18c0:       ff 35 0a 22 00 00       pushq  0x220a(%rip)        # 3ad0 <__init_array_end+0x1190>
      18c6:       ff 25 0c 22 00 00       jmpq   *0x220c(%rip)        # 3ad8 <__init_array_end+0x1198>
      18cc:       0f 1f 40 00             nopl   0x0(%rax)
      18d0:       f3 0f 1e fa             endbr64 
      18d4:       68 00 00 00 00          pushq  $0x0
      18d9:       e9 e2 ff ff ff          jmpq   18c0 <_fini+0x14>
      18de:       66 90                   xchg   %ax,%ax
      18e0:       f3 0f 1e fa             endbr64 
      18e4:       68 01 00 00 00          pushq  $0x1
      18e9:       e9 d2 ff ff ff          jmpq   18c0 <_fini+0x14>
      18ee:       66 90                   xchg   %ax,%ax
      18f0:       f3 0f 1e fa             endbr64 
      18f4:       68 02 00 00 00          pushq  $0x2
      18f9:       e9 c2 ff ff ff          jmpq   18c0 <_fini+0x14>
      18fe:       66 90                   xchg   %ax,%ax
  
  Disassembly of section .plt.sec:
  
  0000000000001900 <.plt.sec>:
      1900:       f3 0f 1e fa             endbr64 
      1904:       ff 25 16 22 00 00       jmpq   *0x2216(%rip)        # 3b20 <__cxa_finalize at GLIBC_2.2.5>
      190a:       66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
      1910:       f3 0f 1e fa             endbr64 
      1914:       ff 25 0e 22 00 00       jmpq   *0x220e(%rip)        # 3b28 <puts at GLIBC_2.2.5>
      191a:       66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
      1920:       f3 0f 1e fa             endbr64 
      1924:       ff 25 06 22 00 00       jmpq   *0x2206(%rip)        # 3b30 <exit at GLIBC_2.2.5>
      192a:       66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)




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