[PATCH] D30256: [ELF] - Implemented -z noreloc-overflow.

[Rui Ueyama via llvm-commits]

On Wed, Feb 22, 2017 at 1:24 PM, George Rimar <grimar at accesssoftek.com>
wrote:

> >I believe GNU linker prints out "relocations against text section;
> recomiple with -fPIC" warning if the linker is creating a DSO. Does >it
> warn on text relocations if no -shared is given?
>
> Depends on relocation. It will show this error for relocations that may be
> truncated in runtime:
> 2594
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2594>
> case R_X86_64_32:
> 2595
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2595>
> if (!ABI_64_P (abfd))
> 2596
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2596>
> goto pointer;
> 2597
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2597> /*
> Fall through. */
> 2598
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2598>
> case R_X86_64_8:
> 2599
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2599>
> case R_X86_64_16:
> 2600
> <https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf64-x86-64.c;h=a058eca3abf03cc2f79601d170b2d6b9f9c459e5;hb=HEAD#l2600>
> case R_X86_64_32S:
>
> But if you take R_X86_64_64:
>
> .text
> .global _start
> _start:
>  .quad _start
>

OK, so this is a separate issue. If a relocation may not be representable
at runtime, the linker prints out a warning. We need to do the same, but
this is a different issue than allowing/disallowing text relocations.


> llvm-mc -filetype=obj -triple=x86_64-pc-linux test.s -o test.o
> ld.bfd test.o -shared -o out
>
> Then no error is produced and DT_TEXTREL is added:
>
>  0x0000000000000016 (TEXTREL)            0x0
>  0x0000000000000000 (NULL)               0x0​
> Relocation section '.rela.dyn' at offset 0x1e0 contains 1 entries:
>   Offset          Info           Type           Sym. Value    Sym. Name +
> Addend
> 0000000001f8  000100000001 R_X86_64_64       00000000000001f8 _start + 0
>

So I think the answer is that the GNU linker doesn't warn on text
relocations at all.
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