search for: outputsect

.../reviews.llvm.org/D25627. > >> >>Problem: >> >>Currently, LLD creates special sections that are not just concatenations of >> input sections but need link-time data generation, such as .got, .plt, >> interp, .mips.options, >etc., as output sections. We have OutputSectionBase >> subclasses (e.g. GotSection, PltSection, etc.) to create data. Even though >> this scheme works in most cases, >there are a few situations that doesn't >> work well as you may have noticed. Here are a issues. >> > >- You cannot mix special sections wi...

...existing InputSections. > > The disadvantage with extra flexibility is that it increases the > amount of opportunities for both implementers and users to make > mistakes, and it makes some implementation details more complicated. > Where we would have been able to guarantee a single OutputSection, we > may have many clumps of InputSections distributed across several > OutputSections. In some cases it is user error to split InputSections > apart as they need to be contiguous, which requites diagnostics, and > in some cases algorithms need to be careful, for example in embedded...

This idea popped up in the review thread for https://reviews.llvm.org/D25627 . Problem: Currently, LLD creates special sections that are not just concatenations of input sections but need link-time data generation, such as .got, .plt, interp, .mips.options, etc., as output sections. We have OutputSectionBase subclasses (e.g. GotSection, PltSection, etc.) to create data. Even though this scheme works in most cases, there are a few situations that doesn't work well as you may have noticed. Here are a issues. - You cannot mix special sections with other types of sections. For example, usin...

...> > Proposed implementation for range extension thunks > > At a high-level we need to solve the following problems: > > - Assign addresses more than once > > - Maintain state between successive calls of createThunks() > > - Synchronization of the linker script and the OutputSection after > adding thunks > > This last past seems to be the messier. The issue is not with the > patch, is with the existing infrastructure that uses a completely > different representation for linker scripts and non linker scripts. > > What I think is needed is for the writer...

...ge Where are we now with LLD and thunks - We have moved the createThunks() function as late as it can be in finalizeSections(), most importantly after all the content has been added to the image. - We only call createThunks() once and we don't calculate addresses before createThunks(). - If an OutputSection is described by a LinkerScript then any thunks created in it are put at the end of the OutputSection. This is due to the LinkerScript not being aware of the thunks (InputSections) in the InputSectionDescriptions. Proposed implementation for range extension thunks At a high-level we need to solv...

...re some comments. >From your arc mapfiles it looks like that in the output both linker's have given the .text output section the correct base address given the alignment restrictions as the alignment requirement of .text from lib_a-memset-bs.o is 4, therefor the alignment requirement of the OutputSection .text should be 4: LLD: Address Size Alignment 00000000 00000080 4 .text 00000000 00000004 1 basic-arc.o:(.text) 00000000 00000000 0 main 00000004 0000007c 4 ... (lib_a-memset-bs.o):(.text) LD .text 0x0000000000000000...

On 2020-11-18, Teresa Johnson via llvm-dev wrote: >AFAIK this effort stalled when Tobias changed jobs. Adding Sergei who may >know the current status of the support within Qualcomm. > >Teresa > >On Wed, Nov 18, 2020 at 11:12 AM Mitra, Gaurav via llvm-dev < >llvm-dev at lists.llvm.org> wrote: > >> Hello All, >> >> >> >> I’d like to pick up

...directive in the file, or pass -mthumb to the assembler via arm-linux-gnu-gcc -Wa,-mthumb (I think). I'm not able to explain what you are seeing in your print out as it doesn't quite match the map file. Looking at your source diff I think I may have found a bug: uint64_t AddrLoc = getOutputSection()->Addr + Offset; RelExpr Expr = Rel.Expr; + if ((Expr == R_PC || Expr == R_GOT_PC) && + (Config->EMachine == EM_ARC_COMPACT || + Config->EMachine == EM_ARC_COMPACT2)) { + uint64_t M = 0; + if (Type == R_ARC_32_PCREL || Type == R_ARC_PC32 || +...

...he storage unit affected by the relocation." For LLD we are calculating the virtual address (VA) of P, as I understand it this is equivalent to the vma used in BFD. Assuming that the relocation is relocating a regular InputSection from the basic-arc.o object then the LLD calculation of P = getOutputSection()->Addr + getOffset(Rel.Offset); translates to: (VA of OutputSection) + (Offset of InputSection within OutputSection) + (Offset within InputSection given by r_offset) The BFD linker seems to be doing the equivalent calculation with an extra modification of the (Offset within InputSection giv...

Hi, I was doing some experiments with LLD and noticed that it pads out OutputSections with null bytes in all cases (as far as I could tell). However, for executable sections on some targets, 0x00 forms part of an executable instruction that is not nop. In particular, for x86_64 targets at least, the sequence 0x00 0x00 is an add instruction. This can result in confusing disassemb...

...olTable::addFile) The frontend work seems to be largely dominated by ObjectFile::parse (as you would expect), though there is about 10% of total runtime slipping through the cracks here in various other "frontend" tasks. The backend work is split about evenly between scanRelocations and OutputSection::writeTo. InputSectionBase::relocate is only about 10% of the total runtime (part of OutputSection::writeTo). Some slightly cleaned up `perf report` output with some more details: https://reviews.llvm.org/P7972 So it seems like overall, the profile is basically split 3 ways (about 30% each): -...

...pt->processNonSectionCommands() // This should only be done once Correct. > In theory all the other __start and __end symbols could still be kept > separate if the linker script commands were created late, and in a > compatible way. I also don't think that this means removing > OutputSections::Sections just yet either? Probably not, but it might got away in the future. > I don't think that we are proposing to follow the ld.bfd model of > driving the default case via a built in linker script yet? I think > that this would be considerably more work than just this limite...

..._RTTI_start = .); > *(.data.rel.ro.RTTI.*) ; PROVIDE_HIDDEN (__RTTI_end = .); > *(.data.rel.ro.local* > .gnu.linkonce.d.rel.ro.local.*) *(.data.rel.ro .data.rel.ro.* > .gnu.linkonce.d.rel.ro.*) } > > This would have your table contiguous in the .data.rel.ro OutputSection > and can be found with the __RTTI_start and __RTTI_end symbols. It may not > work so well if you are using SHF_LINK_ORDER for the RTTI sections as some > linkers tend to handle these better when every InputSection in the > OutputSection has SHF_LINK_ORDER. > > Peter > >...

Hi Rafael, On 07/31/2017 04:20 PM, Rafael Avila de Espindola via llvm-dev wrote: > However, do we need to start with instrumentation? The original paper > uses sampling with good results and current intel cpus can record every > branch in a program. > > I would propose starting with just an lld patch that reads the call > graph from a file. The format would be very similar to

Hey, We would like to propose an idea that would help security harden applications that define custom sections. Motivation and Background In Chromium we have a garbage collector that implements some RTTI machinery in the form of a table. This table is used by the collector to trace and finalize garbage collected objects. We're thinking of using __attribute__((section(...))) so that the table

...o be largely dominated by ObjectFile::parse (as >> you would expect), though there is about 10% of total runtime slipping >> through the cracks here in various other "frontend" tasks. >> >> The backend work is split about evenly between scanRelocations and >> OutputSection::writeTo. InputSectionBase::relocate is only about 10% of the >> total runtime (part of OutputSection::writeTo). >> >> Some slightly cleaned up `perf report` output with some more details: >> https://reviews.llvm.org/P7972 >> >> So it seems like overall, the p...

We have fairly large and complex code to handle relocations in Writer.cpp, Target.cpp, OutputSections.cpp and InputSections.cpp. They started with simple code, but because each patch added a small piece of code to the existing one, it is becoming out of control now. For example, we have lots of entangled boolean flags in the functions that interfere with each other in an obscure fashion. Even I...

...d if the output section is > different. > Correct. Plus, others can be enabled if they're safe to apply when we know things are going to the same output section. > The common use cases that I can see that might not fit perfectly into > that model: > - Code that is in different OutputSections but it will be logically > correct and in many cases desirable to perform transformations on as > if they were in the same output section. Right. The output section that the linker communicates for a symbol doesn't need to correspond to a "physical" output section. So let&...

...StringSwitch.h" #include "llvm/Support/FileOutputBuffer.h" #include "llvm/Support/raw_ostream.h" #include <climits> +#include <unordered_set> using namespace llvm; using namespace llvm::ELF; @@ -922,6 +924,157 @@ static void sortBySymbolsOrder(ArrayRef<OutputSection *> OutputSections) { Sec->sort([&](InputSectionBase *S) { return SectionOrder.lookup(S); }); } +// Sort sections by the profile data provided in the .note.llvm.callgraph +// sections. +// +// This algorithm is based on Call-Chain Clustering from: +// Optimizing Function Place...

...he sizes and addresses of all the SyntheticSections are known. This would mean that the final address of each caller and callee could be used, and after thunk creation there would be no further content changes. This would mean: - All code that runs prior to thunk creation may have the offset in the OutputSection altered by the addition of thunks. In particular scanRelocs() calculates the offset in the OutputSection of some relocations. We would need to find alternative ways of handling these cases so that they could either survive thunk creation or be patched up afterwards. - assignAddresses() will need...