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

[Renlin Li <renlin dot li at foss dot arm dot com>]

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.



diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 23c881c..bdc7c80 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -7058,11 +7058,17 @@ elfNN_aarch64_check_relocs (bfd *abfd, struct bfd_link_info *info,
 
       switch (bfd_r_type)
 	{
+	case BFD_RELOC_AARCH64_16:
+#if ARCH_SIZE == 64
+	case BFD_RELOC_AARCH64_32:
+#endif
 	case BFD_RELOC_AARCH64_MOVW_G0_NC:
 	case BFD_RELOC_AARCH64_MOVW_G1_NC:
 	case BFD_RELOC_AARCH64_MOVW_G2_NC:
 	case BFD_RELOC_AARCH64_MOVW_G3:
-	  if (bfd_link_pic (info))
+	  if (bfd_link_pic (info)
+	      && (sec->flags & SEC_ALLOC) != 0
+	      && (sec->flags & SEC_READONLY) != 0)
 	    {
 	      int howto_index = bfd_r_type - BFD_RELOC_AARCH64_RELOC_START;
 	      _bfd_error_handler
diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp b/ld/testsuite/ld-aarch64/aarch64-elf.exp
index b9c9885..fbc4f86 100644
--- a/ld/testsuite/ld-aarch64/aarch64-elf.exp
+++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp
@@ -103,6 +103,8 @@ run_dump_test_lp64 "emit-relocs-257"
 run_dump_test_lp64 "emit-relocs-257-be"
 # 258 is tested in 257
 # 259 is tested in 257
+run_dump_test "emit-relocs-258-dyn-bad"
+run_dump_test "emit-relocs-259-dyn-bad"
 run_dump_test_lp64 "emit-relocs-260"
 run_dump_test_lp64 "emit-relocs-260-be"
 # 261 is tested by 260
diff --git a/ld/testsuite/ld-aarch64/emit-relocs-258-dyn-bad.d b/ld/testsuite/ld-aarch64/emit-relocs-258-dyn-bad.d
new file mode 100644
index 0000000..cbd4577
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/emit-relocs-258-dyn-bad.d
@@ -0,0 +1,4 @@
+#name: LP64 R_AARCH64_ABS32 shared library test
+#source: emit-relocs-258.s
+#ld: -shared
+#error: .*: relocation R_AARCH64_ABS32 against `dummy' can not be used when making a shared object; recompile with -fPIC
diff --git a/ld/testsuite/ld-aarch64/emit-relocs-258.s b/ld/testsuite/ld-aarch64/emit-relocs-258.s
new file mode 100644
index 0000000..f724776
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/emit-relocs-258.s
@@ -0,0 +1,6 @@
+.text
+
+  ldr x0, .L1
+
+.L1:
+  .word dummy
diff --git a/ld/testsuite/ld-aarch64/emit-relocs-259-dyn-bad.d b/ld/testsuite/ld-aarch64/emit-relocs-259-dyn-bad.d
new file mode 100644
index 0000000..6e111c6e
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/emit-relocs-259-dyn-bad.d
@@ -0,0 +1,4 @@
+#name: R_AARCH64_ABS16 shared library test
+#source: emit-relocs-259.s
+#ld: -shared
+#error: .*: relocation R_AARCH64_ABS16 against `dummy' can not be used when making a shared object; recompile with -fPIC
diff --git a/ld/testsuite/ld-aarch64/emit-relocs-259.s b/ld/testsuite/ld-aarch64/emit-relocs-259.s
new file mode 100644
index 0000000..7e1ba3c
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/emit-relocs-259.s
@@ -0,0 +1,6 @@
+.text
+
+  ldr x0, .L1
+
+.L1:
+  .hword dummy
diff --git a/ld/testsuite/ld-aarch64/gc-relocs-257.s b/ld/testsuite/ld-aarch64/gc-relocs-257.s
index dcc9db1..f57f9c6 100644
--- a/ld/testsuite/ld-aarch64/gc-relocs-257.s
+++ b/ld/testsuite/ld-aarch64/gc-relocs-257.s
@@ -1,8 +1,10 @@
 	.text
-	.word   tempy
+	and	x0, x0, x0
+	and	x0, x0, #0x1
 	.xword  tempy2
+
+	.data
+	.word   tempy
 	.hword  tempy3
 	.hword  tempy3+8
 
-	and	x0, x0, x0
-	and	x0, x0, #0x1