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

[infinity0]

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.

[andybons]

@ianlancetaylor

[ianlancetaylor]

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.

[gopherbot]

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.)

[FiloSottile]

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

[andybons]

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

[pwaller]

@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.

        .text
        .file   "-"
        .globl  exampleFunc      # -- Begin function exampleFunc
        .p2align        4, 0x90
        .type   exampleFunc,@function
exampleFunc:                     # @exampleFunc
.Lfunc_begin0:
        .cfi_startproc
        movzbl  .L__const.exampleFunc.one(%rip), %eax
        movl    %eax, 8(%rsp)
        retq
.Lfunc_end0:
        .size   exampleFunc, .Lfunc_end0-exampleFunc
        .cfi_endproc

        .type   .L__const.exampleFunc.one,@object # @__const.exampleFunc.one
        .section        .rodata.cst4,"aM",@progbits,4
        .p2align        2
.L__const.exampleFunc.one:
        .long   1                       # 0x1
        .size   .L__const.exampleFunc.one, 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() {
        println(exampleFunc())
}

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        .L__const.exampleFunc.one-0x4
   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