Commit Graph

5 Commits

Author SHA1 Message Date
Jason W Kim
861b9c6a39 This fixes one divergence between LLVM and binutils for ARM in the
text section.

Assume the following bit of annotated assembly:

.section	.data.rel.ro,"aw",%progbits
.align	2
.LAlpha:
.long	startval(GOTOFF)

.text
.align	2
.type	main,%function
.align	4

main: ;;; assume "main" starts at offset 0x20
0x0	push	{r11, lr}
0x4	movw	r0, :lower16:(.LAlpha-(.LBeta+8))
;;; ==> (.AddrOf(.LAlpha) - ((.AddrOf(.LBeta) - .AddrOf(".")) + 8)
;;; ==> (??? - ((16-4) + 8) = -20
0x8	movt	r0, :upper16:(.LAlpha-(.LBeta+8))
;;; ==> (.AddrOf(.LAlpha) - ((.AddrOf(.LBeta) - .AddrOf(".")) + 8)
;;; ==> (??? - ((16-8) + 8) = -16
0xc	... blah

.LBeta:
0x10	add	r0, pc, r0
0x14	... blah

.LGamma:
0x18	add	r1, pc, r1

Above snippet results in the following relocs in the .o file for the
first pair of movw/movt instructions

00000024 R_ARM_MOVW_PREL_NC .LAlpha
00000028 R_ARM_MOVT_PREL .LAlpha

And the encoded instructions in the .o file for main: must be

00000020 <main>:
20:	e92d4800 push	{fp, lr}
24:	e30f0fec movw	r0, #65516	; 0xffec i.e. -20
28:	e34f0ff0 movt	r0, #65520	; 0xfff0 i.e. -16

However, llc (prior to this commit) generates the following sequence

00000020 <main>:
20:	e92d4800 push	{fp, lr}
24:	e30f0fec movw	r0, #65516	; 0xffec - i.e. -20
28:	e34f0fff movt	r0, #65535	; 0xffff - i.e. -1

What has to happen in the ArmAsmBackend is that if the relocation is PC
relative, the 16 bits encoded as part of movw and movt must be both addends,
not addresses. It makes sense to encode addresses by right shifting the value
by 16, but the result is incorrect for PIC.
i.e., the right shift by 16 for movt is ONLY valid for the NON-PCRel case.

This change agrees with what GNU as does, and makes the PIC code run.

MC/ARM/elf-movt.s covers this case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131674 91177308-0d34-0410-b5e6-96231b3b80d8
2011-05-19 20:55:25 +00:00
Evan Cheng
f3eb3bba16 Completed :lower16: / :upper16: support for movw / movt pairs on Darwin.
- Fixed :upper16: fix up routine. It should be shifting down the top 16 bits first.
- Added support for Thumb2 :lower16: and :upper16: fix up.
- Added :upper16: and :lower16: relocation support to mach-o object writer.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123424 91177308-0d34-0410-b5e6-96231b3b80d8
2011-01-14 02:38:49 +00:00
Evan Cheng
7597212abc Model :upper16: and :lower16: as ARM specific MCTargetExpr. This is a step
in the right direction. It eliminated some hacks and will unblock codegen
work. But it's far from being done. It doesn't reject illegal expressions,
e.g. (FOO - :lower16:BAR). It also doesn't work in Thumb2 mode at all.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123369 91177308-0d34-0410-b5e6-96231b3b80d8
2011-01-13 07:58:56 +00:00
Jason W Kim
86a97f2e4d 1. Support ELF pcrel relocations for movw/movt:
R_ARM_MOVT_PREL and R_ARM_MOVW_PREL_NC.
2. Fix minor bug in ARMAsmPrinter - treat bitfield flag as a bitfield, not an enum.
3. Add support for 3 new elf section types (no-ops)




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123294 91177308-0d34-0410-b5e6-96231b3b80d8
2011-01-12 00:19:25 +00:00
Jason W Kim
9081b4b4cf Workaround for bug 8721.
.s Test added.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123292 91177308-0d34-0410-b5e6-96231b3b80d8
2011-01-11 23:53:41 +00:00