Re: [BFD][AARCH64]Disallow R_AARCH64_ABS32(LP64) & R_AARCH64_ABS16 in const section of shared object

[Matthias Klose <doko at ubuntu dot com>]

This seems to break kernel builds, and linking systemd against gnu-efi
libraries.  Now reported in PR22764.

Matthias

On 18.10.2017 12:40, Renlin Li wrote:
> Hi all,
> 
> R_AARCH64_ABS64, R_AARCH64_ABS32 and R_AARCH64_ABS16 are data relocations
> supported in AArch64 elf ABI.
> 
> R_AARCH64_ABS64 under LP64 is allowed in shared object and a dynamic relocation
> entry
> will be generated. This allows the dynamic linker to do further symbol resolution.
> 
> R_AARCH64_ABS32 likewise is allowed in shared object, however under ILP32 abi.
> 
> The original behavior for R_AARCH64_ABS32 under LP64 is that, it's allowed
> in shared object and silently resolved at static linking time.
> No dynamic relocation entry is generate for it.
> 
> R_AARCH64_ABS16 is allowed in shared object under both L64 and ILP32.
> It's resolved at static linking time as well.
> 
> Under LP64, the address should be 64-bit. R_AARCH64_ABS32 relocation indicates
> an address that is only sized 32 bits which is not correct in LP64 shared object.
> It's useful to error out.
> 
> I have checked glibc dynamic linker code, R_AARCH64_ABS16 is not supported at
> all. So
> R_AARCH64_ABS16 should be reject in shared object completely.
> 
> 
> In this patch, R_AARCH64_ABS32 is rejected under LP64 in read-only section of
> shared object.
> R_AARCH64_ABS16 is rejected in constant section of shared object in both ABI.
> 
> This will sometimes provide useful information for buggy code.
> 
> By the way, glibc aarch64 elf_machine_load_address is using R_AARCH64_ABS32 to
> hold an address even in LP64. I had a discussion here sometime ago. The change
> here will break the glibc build. This patch will not be committed until glibc
> has been fixed.
> https://sourceware.org/ml/libc-alpha/2017-10/msg00816.html
> 
> testcases are also added. Binutils regression checked OK.
> Linux kernel linked OK with new binutils. OK for trunk?
> 
> 
> Regards,
> Renlin Li
> 
> 
> ld/ChangeLog:
> 
> 2017-10-18  Renlin Li  <renlin.li@arm.com>
> 
>     * testsuite/ld-aarch64/aarch64-elf.exp: Run new test cases.
>     * testsuite/ld-aarch64/emit-relocs-258-dyn-bad.d: New.
>     * testsuite/ld-aarch64/emit-relocs-258.s: New.
>     * testsuite/ld-aarch64/emit-relocs-259-dyn-bad.d: New.
>     * testsuite/ld-aarch64/emit-relocs-259.s: New.
>     * testsuite/ld-aarch64/gc-relocs-257.s: Put R_AARCH64_ABS32,
>     R_AARCH64_ABS16 data into data section.
> 
> bfd/ChangeLog:
> 
> 2017-10-18  Renlin Li  <renlin.li@arm.com>
> 
>     * elfnn-aarch64.c (elfNN_aarch64_check_relocs): Disallow
>     BFD_RELOC_AARCH64_16 in shared object const section. Disallow
>     BFD_RELOC_AARCH64_32 in shared object const section under LP64.
> 
> 
>