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cmd/link: silently performs incorrect relocations when linking foreign objects #24321

infinity0 opened this issue Mar 9, 2018 · 6 comments


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@infinity0 infinity0 commented Mar 9, 2018

For example, when linking syso files.

Adding go:cgo_import_dynamic helps but (1) it was recently disabled for security reasons for non-cgo files, then reenabled because solaris needs it, so it's unclear if this policy will persist in the long-run for all architectures, and (2) you need to specify it for specific symbols rather than for all symbols. In any case, an error should be raised with a hint on what to do, rather than succeeding silently with invalid output.

The equivalent thing in Haskell Just Works with no extra annotations.

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@andybons andybons commented Mar 9, 2018

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@ianlancetaylor ianlancetaylor commented Mar 9, 2018

Can you show us a self-contained example?

Does it work if you use -ldflags=-linkmode=external?

Perhaps we should default to external linking mode in the presence of any syso files.

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@gopherbot gopherbot commented Apr 12, 2018

Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)

@gopherbot gopherbot closed this Apr 12, 2018
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@FiloSottile FiloSottile commented Apr 12, 2018

Reopening, I can provide a test case from FiloSottile/ed25519-dalek-rustgo#1.

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@andybons andybons commented Apr 13, 2018

Removing the WaitingForInfo tag worked around GopherBot fighting you :P.

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@pwaller pwaller commented Mar 26, 2019

@ianlancetaylor I encountered this issue while looking into #30890.

Also, whilst typing in my issue number I discovered the very next issue filed was also about relocations - interesting/amusing coincidence: #30891.

        .file   "-"
        .globl  exampleFunc      # -- Begin function exampleFunc
        .p2align        4, 0x90
        .type   exampleFunc,@function
exampleFunc:                     # @exampleFunc
        movzbl, %eax
        movl    %eax, 8(%rsp)
        .size   exampleFunc, .Lfunc_end0-exampleFunc

        .type,@object #
        .section        .rodata.cst4,"aM",@progbits,4
        .p2align        2
        .long   1                       # 0x1
        .size, 4

If I build this with as to produce a syso and go build, the relocation is missing in the resulting binary.

TEXT ·exampleFunc(SB),$0-8
  JMP exampleFunc(SB)
package main

func main() {

func exampleFunc() uint

objdump -dr shows the relocation in the syso:

0000000000000000 <exampleFunc>:
   0:   0f b6 05 00 00 00 00    movzbl 0x0(%rip),%eax        # 7 <exampleFunc+0x7>
                        3: R_X86_64_PC32
   7:   89 04 24                mov    %eax,8(%rsp)
   a:   c3                      retq   

but it's missing in the go binary:

0000000000401000 <exampleFunc>:
  401000:       0f b6 05 00 00 00 00    movzbl 0x0(%rip),%eax        # 401007 <exampleFunc+0x7>
  401007:       89 04 24                mov    %eax,8(%rsp)
  40100a:       c3                      retq   

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