[llvm-dev] ld.lld drops relocations (original) (raw)

Tomasz Paweł Gajc via llvm-dev llvm-dev at lists.llvm.org
Tue Mar 16 01:27:00 PDT 2021

Dnia poniedziałek, 15 marca 2021 23:21:11 CET Fāng-ruì Sòng pisze:

On Mon, Mar 15, 2021 at 3:00 PM David Blaikie <dblaikie at gmail.com> wrote: > +Fangrui Song > _> On Mon, Mar 15, 2021 at 2:57 PM Tomasz Gajc via llvm-dev <llvm-_ dev at lists.llvm.org> wrote: >> Hi, >> >> i'm trying to dig issue with building systemd-boot EFI images with >> llvm/clang and linking with llvm/lld. In general building and linking >> process works and i get my final objects. Unfortunately these EFI images >> does not boot system. I noticed that .efi image is missing PE/COFF >> relocations. When i changed linker to ld.bfd, voila everything is fine >> and final efi image does boot system and have needed relocs. I tried all[689/2941] ld.bfd -o src/boot/efi/systemd_boot.so -T /usr/lib64/gnuefi/ elf_x86_64_efi.lds -shared -Bsymbolic -nostdlib -znocombreloc -L /usr/lib64 / usr/lib64/gnuefi/crt0-efi-x86_64.o src/boot/efi/disk.c.o src/boot/efi/ graphics.c.o src/boot/efi/measure.c.o src/boot/efi/pe.c.o src/boot/efi/ util.c.o src/boot/efi/boot.c.o src/boot/efi/console.c.o src/boot/efi/crc32.c.o src/boot/efi/random-seed.c.o src/boot/efi/sha256.c.o src/boot/efi/shim.c.o - lefi -lgnuefi /usr/lib64/gcc/x86_64-openmandriva-linux-gnu/10.2.1/libgcc.a [690/2941] /usr/bin/clang -Isystemd-resolved.p -I. -I.. -Isrc/basic -I../src/ basic -Isrc/boot -I../ >> the ld.lld options related to relocations, but still no success. Thanks >> for your help. >> >> Below you can find diff between two objdumps. >> >> [root at tpg-latitude5490 /]# cat bootx.linkers.diff >> --- bootx.BFD 2021-03-14 23:33:41.687446710 +0100 >> +++ bootx.LLD 2021-03-14 23:33:58.037519874 +0100 >> @@ -1,11 +1,12 @@ >> >> -systemd-bootx64.efi.BFD: file format pei-x86-64 >> -systemd-bootx64.efi.BFD >> -architecture: i386:x86-64, flags 0x00000133: >> -HASRELOC, EXECP, HASSYMS, HASLOCALS, DPAGED >> -start address 0x0000000000003000 >> +systemd-bootx64.efi.LLD: file format pei-x86-64 >> +systemd-bootx64.efi.LLD >> +architecture: i386:x86-64, flags 0x00000132: >> +EXECP, HASSYMS, HASLOCALS, DPAGED >> +start address 0x0000000000004000 >> >> -Characteristics 0x206 >> +Characteristics 0x207 >> + relocations stripped >> >> executable >> line numbers stripped >> debugging information removed >> >> @@ -14,11 +15,11 @@ >> >> Magic 020b (PE32+) >> MajorLinkerVersion 2 >> MinorLinkerVersion 36 >> >> -SizeOfCode 0000000000010000 >> -SizeOfInitializedData 0000000000006000 >> +SizeOfCode 000000000000f600 >> +SizeOfInitializedData 0000000000005e00 >> >> SizeOfUninitializedData 0000000000000000 >> >> -AddressOfEntryPoint 0000000000003000 >> -BaseOfCode 0000000000003000 >> +AddressOfEntryPoint 0000000000004000 >> +BaseOfCode 0000000000004000 >> >> ImageBase 0000000000000000 >> SectionAlignment 00001000 >> FileAlignment 00000200 >> >> @@ -29,9 +30,9 @@ >> >> MajorSubsystemVersion 0 >> MinorSubsystemVersion 0 >> Win32Version 00000000 >> >> -SizeOfImage 0001c000 >> -SizeOfHeaders 00000400 >> -CheckSum 00022f3d >> +SizeOfImage 0001b000 >> +SizeOfHeaders 00000370 >> +CheckSum 0001b531 >> >> Subsystem 0000000a (EFI application) >> DllCharacteristics 00000000 >> SizeOfStackReserve 0000000000000000 >> >> @@ -47,7 +48,7 @@ >> >> Entry 2 0000000000000000 00000000 Resource Directory [.rsrc] >> Entry 3 0000000000000000 00000000 Exception Directory [.pdata] >> Entry 4 0000000000000000 00000000 Security Directory >> >> -Entry 5 0000000000013000 0000000a Base Relocation Directory [.reloc] >> +Entry 5 0000000000000000 00000000 Base Relocation Directory [.reloc] >> >> Entry 6 0000000000000000 00000000 Debug Directory >> Entry 7 0000000000000000 00000000 Description Directory >> Entry 8 0000000000000000 00000000 Special Directory >> >> @@ -59,367 +60,358 @@ >> >> Entry e 0000000000000000 00000000 CLR Runtime Header >> Entry f 0000000000000000 00000000 Reserved >> >> - >> -PE File Base Relocations (interpreted .reloc section contents) >> - >> -Virtual Address: 00004770 Chunk size 10 (0xa) Number of fixups 1 >> - reloc 0 offset 0 [4770] ABSOLUTE >> - >> >> Sections: >> Idx Name Size VMA LMA File off >> Algn>> >> - 0 .text 0000ff20 0000000000003000 0000000000003000 00000400 >> 2**4 - CONTENTS, ALLOC, LOAD, READONLY, CODE >> - 1 .reloc 0000000a 0000000000013000 0000000000013000 00010400 >> 2**0 + 0 .rela.dyn 00000fa8 0000000000000170 0000000000000170 >> 00000370 2**3>> >> CONTENTS, ALLOC, LOAD, READONLY, DATA >> >> - 2 .data 00004460 0000000000014000 0000000000014000 00010600 >> 2**5 + 1 .text 0000f510 0000000000004000 0000000000004000 >> 00001400 2**4 + CONTENTS, ALLOC, LOAD, READONLY, CODE >> + 2 .data 00004578 0000000000014000 0000000000014000 00010a00 >> 2**5>> >> CONTENTS, ALLOC, LOAD, DATA >> >> - 3 .dynamic 000000f0 0000000000019000 0000000000019000 00014c00 >> 2**3 + 3 .dynamic 000000a0 0000000000019000 0000000000019000 >> 00015000 2**3>> >> CONTENTS, ALLOC, LOAD, DATA >> >> - 4 .rela 00000fa8 000000000001a000 000000000001a000 00014e00 >> 2**3 - CONTENTS, ALLOC, LOAD, READONLY, DATA >> - 5 .dynsym 000004e0 000000000001b000 000000000001b000 00015e00 >> 2**3 + 4 .dynsym 00000450 000000000001a000 000000000001a000 >> 00015200 2**3>> >> CONTENTS, ALLOC, LOAD, READONLY, DATA >> >> 1. [systemd issue] - https://github.com/systemd/systemd/issues/19005 _>> ________________________ >> LLVM Developers mailing list >> llvm-dev at lists.llvm.org >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Is this ld.lld (ELF) or lld-link (PE-COFF)? lld is a crunchgen style linker which supports multiple binary formats. This is ld.lld snapshot of 12.0.0 from 2021-03-05

I have seen two ways producing an EFI binary. Both are largely underspecified.

* ld.bfd -m $anelfemulation => objcopy -I elf64-x86-64 -O efi-app-x8664. This converts an ELF binary to a PE-COFF binary in a largely underspecified way. It is not clearly how objcopy translates the ELF sections and relocations. * ld.bfd -m $anpeemulation (no objcopy). This should correspond to lld-link. In lld-link, /fixed causes config->relocatable=false, which eventually sets the IMAGEFILERELOCSSTRIPPED flag. It seems that GNU ld does something a bit differently. bfd/peXXigen.c

This is how a ld.bfd linking looks like : [689/2941] ld.bfd -o src/boot/efi/systemd_boot.so -T /usr/lib64/gnuefi/ elf_x86_64_efi.lds -shared -Bsymbolic -nostdlib -znocombreloc -L /usr/lib64 / usr/lib64/gnuefi/crt0-efi-x86_64.o src/boot/efi/disk.c.o src/boot/efi/ graphics.c.o src/boot/efi/measure.c.o src/boot/efi/pe.c.o src/boot/efi/ util.c.o src/boot/efi/boot.c.o src/boot/efi/console.c.o src/boot/efi/crc32.c.o src/boot/efi/random-seed.c.o src/boot/efi/sha256.c.o src/boot/efi/shim.c.o - lefi -lgnuefi /usr/lib64/gcc/x86_64-openmandriva-linux-gnu/10.2.1/libgcc.a [690/2941] /usr/bin/clang -Isystemd-resolved.p -I. -I.. -Isrc/basic -I../src/ basic -Isrc/boot -I../

And here is the meson.build https://github.com/systemd/systemd/blob/main/src/ boot/efi/meson.build

/* For PIE, if there is .reloc, we won't add IMAGEFILERELOCSSTRIPPED. But there is no .reloc, we make sure that IMAGEFILERELOCSSTRIPPED won't be added. */ if (! pedata (ibfd)->hasrelocsection && ! (pedata (ibfd)->realflags & IMAGEFILERELOCSSTRIPPED)) pedata (obfd)->dontstripreloc = 1;

One may need to debug ld.bfd to understand how it works.

This sounds like i should file a bug report for llvm/lld for missing "feature".

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