similar to: [RFC][LLD][ARM] Initial ARM port for LLD

Hello Rui, Thanks for the comments - Synthetic sections and rewriting relocations I think that this would definitely be worth trying. It should remove the need for thunks to be represented in the core data structures, and would allow . It would also mean that we wouldn't have to associate symbols with thunks as the relocations would directly target the thunks. ARM interworking makes reusing

I'm about to start working on range extension thunks in lld. This is an attempt to summarize the approach I'd like to take and what the impact will be on lld outside of thunks. I'm interested if anyone has any constraints the approach will break, alternative suggestions, or is working on something I'll need to take account of? I expect range extension thunks to be important for

I've been working on supporting ARM/Thumb interworking thunks in LLD and have encountered a limitation that I think it is worth bringing up in a wider context. This is all LLD specific, apologies if I've abused llvm-dev here. TL;DR summary: - Thunks in lld may not work if they are added to InputSections that have already been scanned. - There is a short term fix, but in the longer term I

First of all thanks for finding the bug. I agree with Rui that right now we can manage without general thunk infrastructure. Let's provide at least a few "thunk" implementation and after that reconsider necessity of common thunk framework. As to MIPS there is one more type of thunk (keyword is .MIPS.stubs) and one more optimization of current thunk (putting a thunk in the beginning

On Fri, Jan 6, 2017 at 6:21 AM, Rui Ueyama via llvm-dev < llvm-dev at lists.llvm.org> wrote: > On Thu, Jan 5, 2017 at 8:15 PM, Peter Smith <peter.smith at linaro.org> > wrote: > >> Hello Rui, >> >> Thanks for the comments >> >> - Synthetic sections and rewriting relocations >> I think that this would definitely be worth trying. It should

After looking at this for a while, I do not think that this problem is NP-hard. With a finite "short branch" displacement k, I was not able to come up with a gadget that could create global constraints as would be needed to e.g. model an instance of 3SAT or vertex cover in terms of this problem. The problem is hard though. I believe that it is likely to be exponential in the "short

Hi, MIPS LA25 thunk is used to call PIC function from non-PIC code. Usually it contains three instructions: lui $25, %hi(func) addiu $25, $25, %lo(func) j func We can write such thunk in an arbitrary place of the generated file. But if a PIC function requires the thunk is the first routine in a section, we can optimize the code and escape jump instruction. To do so we just write the

On Wed, Aug 26, 2015 at 11:49:46AM -0400, Rafael Espíndola wrote: > This is pr10368. > > Do we really need to support hard coded relocation numbers? Looks like > the examples above have a representation as constant expressions: > > (sub (add (ptrtoint @foo) 0xeafffffe) cur_pos) > > no? I'm not sure if this would be sufficient. The R_ARM_JUMP24 relocation on ARM

On Wed, Aug 26, 2015 at 03:53:33PM -0400, Rafael Espíndola wrote: > > I'm not sure if this would be sufficient. The R_ARM_JUMP24 relocation > > on ARM has specific semantics to implement ARM/Thumb interworking; see > > http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044e/IHI0044E_aaelf.pdf > > Note that R_ARM_CALL has the same operation but different semantics.

This RFC is primarily to support the review of the range extension thunks implementation of lld. This concerns ARM and Mips as all of the thunk creation step is skipped over if the target doesn't need thunks. Mips LA25 Thunks are not range extension Thunks but these are generated using the same code, I've kept the behaviour the same as it is now, although the implementation is obviously

On Jan 19, 2017 2:48 AM, "Ed Maste" <emaste at freebsd.org> wrote: On 4 January 2017 at 13:34, Peter Smith via llvm-dev <llvm-dev at lists.llvm.org> wrote: > I'm about to start working on range extension thunks in lld. This is > an attempt to summarize the approach I'd like to take and what the > impact will be on lld outside of thunks. Now that LLD works

On Fri, Oct 7, 2016 at 12:20 PM, Evgenii Stepanov <eugeni.stepanov at gmail.com > wrote: > I've tried implementing some of the alternatives mentioned in this > thread, and so far I like this syntax the most: > > i32 reloc (29, void ()* @f, 3925868544) > ; 29 = 0x1d = R_ARM_JUMP24 > ; 3925868544 = 0xea000000 > > Note the zeroes in the relocated data instead of

I noticed that LLD doesn’t preserve the symbol type for a defsym directive. For example: $ cat f.c void f() {} $ clang -c f.c $ ld.lld -shared --defsym=g=f f.o $ objdump -T a.out DYNAMIC SYMBOL TABLE: 00000000000012a0 g DF .text 0000000000000006 f 00000000000012a0 g D .text 0000000000000000 g f is marked as a function symbol, but g is not. I recognize this is hard to do in the general

On Fri, Oct 7, 2016 at 1:55 PM, Evgenii Stepanov <eugeni.stepanov at gmail.com> wrote: > On Fri, Oct 7, 2016 at 1:22 PM, Peter Collingbourne <peter at pcc.me.uk> > wrote: > > On Fri, Oct 7, 2016 at 12:20 PM, Evgenii Stepanov > > <eugeni.stepanov at gmail.com> wrote: > >> > >> I've tried implementing some of the alternatives mentioned in

I'm not aware of a written guide either. In 2016 I did a talk on that subject at the LLVM Cauldron (http://llvm.org/devmtg/2016-09/#schedule) although quite a bit has changed since then so I'm hesitant to recommend it apart from general principles. I can't speak for the COFF side as I've only worked on the ELF side of LLD; my suggestions on where to start: - Properties of the

Hi, Sorry for delay with reply. It looks like now thunks can be implemented as a synthetic sections. In that case we give flexible solution and will be able to put thunks before/after related sections, using different alignment etc. As far as I know BFD linker uses the same approach at least for MIPS thunks. I will try to implement this idea. On Thu, Sep 8, 2016 at 1:44 AM, Rui Ueyama <ruiu

On Fri, Oct 7, 2016 at 2:48 PM, Evgenii Stepanov <eugeni.stepanov at gmail.com> wrote: > On Fri, Oct 7, 2016 at 2:28 PM, Peter Collingbourne <peter at pcc.me.uk> > wrote: > > On Fri, Oct 7, 2016 at 1:55 PM, Evgenii Stepanov < > eugeni.stepanov at gmail.com> > > wrote: > >> > >> On Fri, Oct 7, 2016 at 1:22 PM, Peter Collingbourne <peter

Hi LLVM-Devs, I am considering switching to using 'llvm-lld' instead of Gnu 'ld' in a future revision of our out-of-tree target, and I am wondering is there a getting started guide for how to go about extending 'llvm-lld' to support an additional target. Thanks, MartinO -------------------------------------------------------------- Intel Research and Development

Sure. One thing I want to remind you is that there is a place in Writer.cpp where we assume all synthetic sections were appended to end of Sections list. Look for `llvm::reverse`. If you add synthetic section thunks right before/after non-synthetic sections, you also want to change that. On Tue, Nov 29, 2016 at 1:18 PM, Simon Atanasyan <simon at atanasyan.com> wrote: > Hi, > >

On Fri, Feb 2, 2018 at 4:36 PM David Woodhouse <dwmw2 at infradead.org> wrote: > On Sat, 2018-02-03 at 00:23 +0000, Chandler Carruth wrote: > > > > Two aspects to this... > > > > One, we're somewhat reluctant to guarantee an ABI here. At least I > > am. While we don't *expect* rampant divergence here, I don't want > > this to become