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

[Renlin Li]

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.



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