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cmd/link: pe .rdata section should not need to be IMAGE_SCN_MEM_EXECUTE #25926

alexbrainman opened this issue Jun 17, 2018 · 3 comments


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@alexbrainman alexbrainman commented Jun 17, 2018

CL 115975 split .text section into .text (code) and .rdata (read only data).

I expected .rdata not to need IMAGE_SCN_MEM_EXECUTE flag set (flag that instructs Windows to allow code execution in that section).

Unfortunately, when I run debug/pe tests, TestInternalLinkerDWARF failed with

--- FAIL: TestInternalLinkerDWARF (0.96s)
    file_test.go:348: running test executable failed: exit status 2 Exception 0xc0000005 0x8 0x4d9058 0x4d9058

        runtime: unknown pc 0x4d9058

I managed to fix test by adding IMAGE_SCN_MEM_EXECUTE to .rdata section. I did not have time to investigate why IMAGE_SCN_MEM_EXECUTE was required, so I just put TODO for later

I had some time to debug this. TestInternalLinkerDWARF builds a.exe executable. I run a.exe in gdb. And I can see that the crash is happening in x_cgo_thread_start. All other functions do have debug information, but this function does not. The asm for x_cgo_thread_start is:

(gdb) disas
Dump of assembler code for function x_cgo_thread_start:
   0x0000000000401330 <+0>:     push   %rbx
   0x0000000000401331 <+1>:     sub    $0x20,%rsp
   0x0000000000401335 <+5>:     mov    %rcx,%rbx
   0x0000000000401338 <+8>:     mov    $0x18,%ecx
=> 0x000000000040133d <+13>:    callq  0x4d9058 <runtime.etypes+24>
   0x0000000000401342 <+18>:    test   %rax,%rax
   0x0000000000401345 <+21>:    je     0x40136a <x_cgo_thread_start+58>
   0x0000000000401347 <+23>:    mov    (%rbx),%rdx
   0x000000000040134a <+26>:    mov    %rax,%rcx
   0x000000000040134d <+29>:    mov    %rdx,(%rax)
   0x0000000000401350 <+32>:    mov    0x8(%rbx),%rdx
   0x0000000000401354 <+36>:    mov    %rdx,0x8(%rax)
   0x0000000000401358 <+40>:    mov    0x10(%rbx),%rdx
   0x000000000040135c <+44>:    mov    %rdx,0x10(%rax)
   0x0000000000401360 <+48>:    add    $0x20,%rsp
   0x0000000000401364 <+52>:    pop    %rbx
   0x0000000000401365 <+53>:    jmpq   0x401430 <_cgo_sys_thread_start>
   0x000000000040136a <+58>:    callq  *0x149cf0(%rip)        # 0x54b060
   0x0000000000401370 <+64>:    mov    $0x2b,%r8d
   0x0000000000401376 <+70>:    mov    $0x1,%edx
   0x000000000040137b <+75>:    lea    0x60(%rax),%r9
   0x000000000040137f <+79>:    lea    0xd4fda(%rip),%rcx        # 0x4d6360 <runtime/cgo(.rdata)>
   0x0000000000401386 <+86>:    callq  0x4d9040 <runtime.etypes>
   0x000000000040138b <+91>:    callq  0x4d9048 <runtime.etypes+8>
   0x0000000000401390 <+96>:    nop

See how call into _beginthread says <runtime.etypes+24> ? It appears _beginthread function end-up in .rdata section.

(gdb) disas
Dump of assembler code for function runtime.etypes:
   0x00000000004d9040 <+0>:     jmpq   *0x54b040
   0x00000000004d9047 <+7>:     nop
   0x00000000004d9048 <+8>:     jmpq   *0x54b058
   0x00000000004d904f <+15>:    nop
   0x00000000004d9050 <+16>:    jmpq   *0x54b050
   0x00000000004d9057 <+23>:    nop
=> 0x00000000004d9058 <+24>:    jmpq   *0x54b038
   0x00000000004d905f <+31>:    nop
   0x00000000004d9060 <+32>:    jmpq   *0x54b048
   0x00000000004d9067 <+39>:    nop
   0x00000000004d9068 <+40>:    add    %al,(%rax)
   0x00000000004d906a <+42>:    add    %al,(%rax)
   0x00000000004d906c <+44>:    add    %al,(%rax)
   0x00000000004d906e <+46>:    add    %al,(%rax)
   0x00000000004d9070 <+48>:    add    %al,(%rax)
   0x00000000004d9072 <+50>:    add    %al,(%rax)
   0x00000000004d9074 <+52>:    add    %al,(%rax)
   0x00000000004d9076 <+54>:    add    %al,(%rax)
   0x00000000004d9078 <+56>:    add    %al,(%rax)
   0x00000000004d907a <+58>:    add    %al,(%rax)
   0x00000000004d907c <+60>:    add    %al,(%rax)
   0x00000000004d907e <+62>:    add    %al,(%rax)
End of assembler dump.
(gdb) si

Program received signal SIGSEGV, Segmentation fault.
0x00000000004d9058 in runtime.etypes ()

It is no surprise that this code cannot execute - it needs IMAGE_SCN_MEM_EXECUTE.

How is _beginthread code

 0x00000000004d9058 <+24>:    jmpq   *0x54b038

end-up in .rdata section? How can we make it go into .text section?

I am hoping that @ianlancetaylor has some ideas about this. :-)


@andybons andybons added this to the Unplanned milestone Jun 18, 2018

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@ianlancetaylor ianlancetaylor commented Jun 18, 2018

I would guess that dope in cmd/link/internal/ld/pe.go should use STEXT rather than SELFROSECT. It looks like the contents of the section, as created in windynrelocsym, are instructions, not read-only data.


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@alexbrainman alexbrainman commented Jul 22, 2018

I would guess that ...

You guessed correctly. I should have guessed it myself. :-)

I think this issue can wait until after go1.11 is released.



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@gopherbot gopherbot commented Jul 22, 2018

Change mentions this issue: cmd/link: move .rel symbol from .rdata into .text

@gopherbot gopherbot closed this in 8256bcd Oct 5, 2018
@golang golang locked and limited conversation to collaborators Oct 5, 2019
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