[PATCH] D95262: [LLD][PowerPC] Fix bug in PC-Relative initial exec

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp added a comment.

I'm sorry, I should have added the full test case.

InitExec.c

  extern __thread unsigned TGlobal;
  unsigned getConst(unsigned*);
  unsigned addVal(unsigned, unsigned*);
  
  unsigned GetAddrT() {
    return addVal(getConst(&TGlobal), &TGlobal);
  }

Def.c

  __thread unsigned TGlobal;
  
  unsigned getConst(unsigned* A) {
    return *A + 3;
  }
  
  unsigned addVal(unsigned A, unsigned* B) {
    return A + *B;
  }

The problem is in InitExec.c but Def.c is required if you want to link the example and see the problem.
To compile everything:

  clang -O3 -mcpu=pwr10 -c InitExec.c
  clang -O3 -mcpu=pwr10 -c Def.c
  ld.lld InitExec.o Def.o -o IeToLe

If you objdump the problem object file:

  $ llvm-objdump -dr --mcpu=pwr10 InitExec.o

you will get the following assembly:

  0000000000000000 <GetAddrT>:
         0: a6 02 08 7c  	mflr 0
         4: f0 ff c1 fb  	std 30, -16(1)
         8: 10 00 01 f8  	std 0, 16(1)
         c: d1 ff 21 f8  	stdu 1, -48(1)
        10: 00 00 10 04 00 00 60 e4      	pld 3, 0(0), 1
  		0000000000000010:  R_PPC64_GOT_TPREL_PCREL34	TGlobal
        18: 14 6a c3 7f  	add 30, 3, 13
  		0000000000000019:  R_PPC64_TLS	TGlobal
        1c: 78 f3 c3 7f  	mr	3, 30
        20: 01 00 00 48  	bl 0x20
  		0000000000000020:  R_PPC64_REL24_NOTOC	getConst
        24: 78 f3 c4 7f  	mr	4, 30
        28: 30 00 21 38  	addi 1, 1, 48
        2c: 10 00 01 e8  	ld 0, 16(1)
        30: f0 ff c1 eb  	ld 30, -16(1)
        34: a6 03 08 7c  	mtlr 0
        38: 00 00 00 48  	b 0x38
  		0000000000000038:  R_PPC64_REL24_NOTOC	addVal

The lines of interest are:

        10: 00 00 10 04 00 00 60 e4      	pld 3, 0(0), 1
  		0000000000000010:  R_PPC64_GOT_TPREL_PCREL34	TGlobal
        18: 14 6a c3 7f  	add 30, 3, 13
  		0000000000000019:  R_PPC64_TLS	TGlobal
        1c: 78 f3 c3 7f  	mr	3, 30

Which once linked get turned into:

  10010210: ff ff 03 06 00 90 6d 38      	paddi 3, 13, -28672, 0
  10010218: 00 00 00 60  	nop
  1001021c: 78 f3 c3 7f  	mr	3, 30

The problem is that register 30 is never set after the optimization.

I'll add it to the description as well. Is this what you were looking for @MaskRay ?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D95262/new/

https://reviews.llvm.org/D95262