[ARM] Relocation counting during check_relocs

[ARM] Relocation counting during check_relocs

[Richard Sandiford]

When linked with -shared, this testcase:

	.globl	foo
foo:
	mov	pc,lr

	.data
	.word	foo-.
	.word	foo-.+0x100

produces two dynamic R_ARM_REL32s against the data section, but this one:

	.globl	foo
foo:
	mov	pc,lr
	bal	foo(PLT)

	.data
	.word	foo-.
	.word	foo-.+0x100

gives the error:

(.data+0x0): dangerous relocation: unsupported relocation
(.data+0x4): dangerous relocation: unsupported relocation

The problem is that elf32_arm_check_relocs only registers a relocation
for R_ARM_REL32 when h->needs_plt is false:

	    if ((info->shared || htab->root.is_relocatable_executable)
		&& (sec->flags & SEC_ALLOC) != 0
		&& ((r_type == R_ARM_ABS32 || r_type == R_ARM_ABS32_NOI)
		    || (h != NULL && ! h->needs_plt
			&& (! info->symbolic || ! h->def_regular))))

But even if h->needs_plt is true, we will only resolve certain types
of relocation to the PLT.  The local "needs_plt" variable says which
types those are, so I think we should be checking that instead.

I thought this might overcount for PIEs, where things like R_ARM_REL32
could in theory refer to the PLT and avoid a dynamic reloc.  However,
it seems that we try to generate a dynamic reloc even there:

	.text
	.globl	_start
_start:
	bl	foo(PLT)

	.data
	.word	foo-.

(linked with -pie) so I think the patch is correct for that case too.

Emitting unnecessary relocs in the PIE case is a separate bug that
I'll try to fix if this patch is OK.  Checking h->needs_plt isn't
enough even then, because we might decide to use a PLT after processing
the current reloc.  I think the right fix is to include a PLT check
in the SYMBOL_CALLS_LOCAL code in elf32_arm_final_link_relocate
and allocate_dynrelocs.

Tested on arm-linux-gnueabi and arm-eabi.  OK to install?

Richard


bfd/
	* elf32-arm.c (elf32_arm_check_relocs): Check needs_plt rather than
	h->needs_plt when deciding whether to record a possible dynamic reloc.

ld/testsuite/
	* ld-arm/arm-rel32.s, ld-arm/arm-rel32.d: New testcase.
	* ld-arm/arm-elf.exp: Run it.

Index: bfd/elf32-arm.c
===================================================================
--- bfd/elf32-arm.c	2010-12-14 15:52:50.000000000 +0000
+++ bfd/elf32-arm.c	2010-12-14 15:56:00.000000000 +0000
@@ -10946,7 +10946,7 @@ elf32_arm_check_relocs (bfd *abfd, struc
 	    if ((info->shared || htab->root.is_relocatable_executable)
 		&& (sec->flags & SEC_ALLOC) != 0
 		&& ((r_type == R_ARM_ABS32 || r_type == R_ARM_ABS32_NOI)
-		    || (h != NULL && ! h->needs_plt
+		    || (h != NULL && ! needs_plt
 			&& (! info->symbolic || ! h->def_regular))))
 	      {
 		struct elf_dyn_relocs *p, **head;
Index: ld/testsuite/ld-arm/arm-rel32.s
===================================================================
--- /dev/null	2010-12-14 12:47:12.274544604 +0000
+++ ld/testsuite/ld-arm/arm-rel32.s	2010-12-14 15:56:00.000000000 +0000
@@ -0,0 +1,8 @@
+	.globl	foo
+foo:
+	mov	pc,lr
+	bal	foo(PLT)
+
+	.data
+	.word	foo-.
+	.word	foo-.+0x100
Index: ld/testsuite/ld-arm/arm-rel32.d
===================================================================
--- /dev/null	2010-12-14 12:47:12.274544604 +0000
+++ ld/testsuite/ld-arm/arm-rel32.d	2010-12-14 15:56:00.000000000 +0000
@@ -0,0 +1,12 @@
+
+.*:     file format .*
+
+DYNAMIC RELOCATION RECORDS
+OFFSET +TYPE +VALUE 
+[^ ]+ R_ARM_REL32 +foo
+[^ ]+ R_ARM_REL32 +foo
+[^ ]+ R_ARM_JUMP_SLOT +foo
+
+
+Contents of section \.data:
+ [^ ]+ 00000000 00010000  .*
Index: ld/testsuite/ld-arm/arm-elf.exp
===================================================================
--- ld/testsuite/ld-arm/arm-elf.exp	2010-12-14 15:52:50.000000000 +0000
+++ ld/testsuite/ld-arm/arm-elf.exp	2010-12-14 15:56:11.000000000 +0000
@@ -126,6 +126,9 @@ set armelftests {
     {"arm-rel31" "-static -T arm.ld" "" {arm-rel31.s}
      {{objdump -s arm-rel31.d}}
      "arm-rel31"}
+    {"arm-rel32" "-shared -T arm-dyn.ld" "" {arm-rel32.s}
+     {{objdump -Rsj.data arm-rel32.d}}
+     "arm-rel32"}
     {"arm-call" "-static -T arm.ld" "-meabi=4" {arm-call1.s arm-call2.s}
      {{objdump -d arm-call.d}}
      "arm-call"}

Re: [ARM] Relocation counting during check_relocs

[Nick Clifton]

Hi Richard,

> bfd/
> 	* elf32-arm.c (elf32_arm_check_relocs): Check needs_plt rather than
> 	h->needs_plt when deciding whether to record a possible dynamic reloc.
>
> ld/testsuite/
> 	* ld-arm/arm-rel32.s, ld-arm/arm-rel32.d: New testcase.
> 	* ld-arm/arm-elf.exp: Run it.

Approved - please apply.

Cheers
   Nick