[llvm-dev] ld.lld drops relocations
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:
> >> -HAS_RELOC, EXEC_P, HAS_SYMS, HAS_LOCALS, D_PAGED
> >> -start address 0x0000000000003000
> >> +systemd-bootx64.efi.LLD: file format pei-x86-64
> >> +systemd-bootx64.efi.LLD
> >> +architecture: i386:x86-64, flags 0x00000132:
> >> +EXEC_P, HAS_SYMS, HAS_LOCALS, D_PAGED
> >> +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 $an_elf_emulation => objcopy -I elf64-x86-64 -O
> efi-app-x86_64. 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 $an_pe_emulation (no objcopy). This should correspond to
> lld-link. In lld-link, /fixed causes config->relocatable=false, which
> eventually sets the IMAGE_FILE_RELOCS_STRIPPED 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 IMAGE_FILE_RELOCS_STRIPPED.
> But there is no .reloc, we make sure that IMAGE_FILE_RELOCS_STRIPPED
> won't be added. */
> if (! pe_data (ibfd)->has_reloc_section
> && ! (pe_data (ibfd)->real_flags & IMAGE_FILE_RELOCS_STRIPPED))
> pe_data (obfd)->dont_strip_reloc = 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".
More information about the llvm-dev
mailing list