[llvm-bugs] [Bug 40740] New: [PowerPC64] [ELFv2] wrong .init section for large binaries (long branch thunk)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40740

            Bug ID: 40740
           Summary: [PowerPC64] [ELFv2] wrong .init section for large
                    binaries (long branch thunk)
           Product: lld
           Version: unspecified
          Hardware: Other
                OS: FreeBSD
            Status: NEW
          Severity: normal
          Priority: P
         Component: ELF
          Assignee: unassignedbugs at nondot.org
          Reporter: alfredo.junior at eldorado.org.br
                CC: llvm-bugs at lists.llvm.org, peter.smith at linaro.org

A large powerpc64 ELFv2 executable linked with lld (i.e. clang) may have an
incorrect .init section and it will crash with SIGTRAP.

In the example bellow, where I'd expect "bl  nnnnn <frame_dummy+0x8>", there's
a "trap" instruction instead, followed by function
"<__long_branch_frame_dummy>":


[root at alfredo-1 /home/alfredo.junior/tmp]# /usr/local/bin/objdump clang -d -j
.init

clang:     file format elf64-powerpc-freebsd


Disassembly of section .init:

0000000013ca9f10 <_init>:
    13ca9f10:   3c 4c 00 1d     addis   r2,r12,29
    13ca9f14:   38 42 76 38     addi    r2,r2,30264
    13ca9f18:   f8 21 ff d1     stdu    r1,-48(r1)
    13ca9f1c:   7c 08 02 a6     mflr    r0
    13ca9f20:   f8 01 00 40     std     r0,64(r1)
    13ca9f24:   7f e0 00 08     trap

0000000013ca9f28 <__long_branch_frame_dummy>:
    13ca9f28:   3d 82 ff e4     addis   r12,r2,-28
    13ca9f2c:   e9 8c bf 00     ld      r12,-16640(r12)
    13ca9f30:   7d 89 03 a6     mtctr   r12
    13ca9f34:   4e 80 04 20     bctr
    13ca9f38:   4b ff ff f1     bl      13ca9f28 <__long_branch_frame_dummy>
    13ca9f3c:   60 00 00 00     nop
    13ca9f40:   4b ff ff 59     bl      13ca9e98 <__do_global_ctors_aux+0x8>
    13ca9f44:   60 00 00 00     nop
    13ca9f48:   e8 21 00 00     ld      r1,0(r1)
    13ca9f4c:   e8 01 00 10     ld      r0,16(r1)
    13ca9f50:   7c 08 03 a6     mtlr    r0
    13ca9f54:   4e 80 00 20     blr



Looks like long-branch-thunk code need to handle .init section as an special
case when the second part of init lands in a higher address.

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