[llvm-dev] ld.lld drops relocations
Tomasz Gajc via llvm-dev
[root@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, DATADavid Blaikie via llvm-dev
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Fāng-ruì Sòng via llvm-dev
Is this ld.lld (ELF) or lld-link (PE-COFF)? lld is a crunchgen style
linker which supports multiple binary formats.
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
/* 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.
Tomasz Paweł Gajc via llvm-dev
> On Mon, Mar 15, 2021 at 3:00 PM David Blaikie <dbla...@gmail.com> wrote:
> > +Fangrui Song
> >
> > On Mon, Mar 15, 2021 at 2:57 PM Tomasz Gajc via llvm-dev <llvm-
d...@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
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../
> 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".