[llvm-dev] ld.lld drops relocations

[Tomasz Gajc via llvm-dev]

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 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
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