[LLVMdev] [lld] question on ELF section formating

[Shankar Easwaran]

It could be any of the following issues :-

a) When writing content overlapped ...
b) The way relocations are applied in X86_64 would be different from 
AARCH64, so could be in the place how relocations are being processed.

Thanks

Shankar Easwaran

On 7/28/2014 3:53 PM, Daniel Stewart wrote:
> I've been adding ELF/AArch64 support to lld based off the existing x86_64
> code that is already there in lld. I've been able to compile and link a
> simple "Hello World"-type program. However, I'm getting what appears to be a
> misplacement/name change of the _start atom. When I do the link, the _start
> section gets named __tls_get_addr. The code inside this section appears to
> be correct, just the name is wrong. If I output in YAML, it appears to have
> the correct name.
>
>   
>
> Since I know this is new code that no one has seen, I was just wondering if
> anyone might give me a hint as to why this might happen or a good place to
> start looking. I'm new to the linker and only have been looking into lld for
> about a week.
>
>   
>
> The output in YAML for the section in question is:
>
>   
>
>    - name:            _start
>
>      scope:           global
>
>      content:         [ 1D, 00, 80, D2, 1E, 00, 80, D2, FD, 03, 00, 91,
>
>                         E5, 03, 00, AA, E1, 03, 40, F9, E2, 23, 00, 91,
>
>                         E6, 03, 00, 91, A0, 00, 00, 58, C3, 00, 00, 58,
>
>                         E4, 00, 00, 58, 00, 00, 00, 94, 00, 00, 00, 94 ]
>
>      alignment:       2^3
>
>      section-name:    .text
>
>      references:
>
>        - kind:            R_AARCH64_CALL26
>
>          offset:          40
>
>          target:          __plt___libc_start_main
>
>        - kind:            R_AARCH64_CALL26
>
>          offset:          44
>
>          target:          __plt_abort
>
>        - kind:            in-group
>
>          offset:          0
>
>          target:          L030
>
>        - kind:            layout-after
>
>          offset:          0
>
>          target:          '$d.010'
>
>   
>
> The output during objdump of that section is:
>
>   
>
> 00000000004006d0 <__tls_get_addr>:
>
>    4006d0:              d280001d             mov       x29, #0x0
> // #0
>
>    4006d4:              d280001e             mov       x30, #0x0
> // #0
>
>    4006d8:              910003fd              mov       x29, sp
>
>    4006dc:               aa0003e5             mov       x5, x0
>
>    4006e0:              f94003e1              ldr           x1, [sp]
>
>    4006e4:              910023e2             add        x2, sp, #0x8
>
>    4006e8:              910003e6             mov       x6, sp
>
>    4006ec:               580000a0             ldr           x0, 400700
> <__tls_get_addr+0x30>
>
>    4006f0:               580000c3              ldr           x3, 400708
> <__tls_get_addr+0x38>
>
>    4006f4:               580000e4             ldr           x4, 400710
> <__tls_get_addr+0x40>
>
>    4006f8:               97ffffe6                bl            400690
> <__libc_start_main at plt>
>
>    4006fc:                97ffffe9                bl            4006a0
> <abort at plt>
>
>    400700:               004008a0             .inst       0x004008a0 ;
> undefined
>
>    400704:               00000000             .inst       0x00000000 ;
> undefined
>
>    400708:               00400934             .inst       0x00400934 ;
> undefined
>
>    40070c:               00000000             .inst       0x00000000 ;
> undefined
>
>    400710:               004009ac              .inst       0x004009ac ;
> undefined
>
>    400714:               00000000             .inst       0x00000000 ;
> undefined
>
>   
>
>   
>
> Daniel
>
>   
>
> --
>
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by
> The Linux Foundation
>
>   
>
>
>
>
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-- 
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