[lld-macho] Support non-pcrel section relocs

[int3]

Summary

Depends on D80854.

[smeenai]

The logic looks good; putting back in your queue for the comment about the test. (Please request review again if I'm just misunderstanding the test.)

lld/MachO/InputFiles.cpp

196

Super nit: even though it's not technically needed, for instances like this where there's a comment within an if (even though there's only a single actual statement), I prefer putting braces around it (and the else), to prevent any possible confusion.

lld/test/MachO/relocations.s

60

Are you missing the corresponding CHECK for this? It would also be nice to add a test with a non-zero offset.

[int3]

address comments

lld/MachO/InputFiles.cpp

196

I prefer that too, just wasn't sure what the prevailing style was supposed to be :)

lld/test/MachO/relocations.s

60

Are you missing the corresponding CHECK for this?

oh yeah good catch

It would also be nice to add a test with a non-zero offset.

L._str is at a non-zero offset in its section, which I think is the important case to test, but yeah I guess it wouldn't hurt to add another reloc whose source is also at a non-zero offset

[smeenai]

LGTM

lld/test/MachO/relocations.s

60

Ah, I'd missed that, but yeah, the second reloc doesn't hurt.

[MaskRay]

Thanks!

lld/test/MachO/relocations.s

32

Rather than saying "This generates a pcrel symbol relocation",
it may be more helpful to just write the relocation type.

[MaskRay]

If I want to check whether lld-macho supports one particular relocation type, I'll grep the source. If the relocation type is literally mentioned in the test, it can help locate the test cases.

[int3]

lld/test/MachO/relocations.s

32

The type doesn't indicate whether it's pcrel or symbol vs section, though, so those bits of info are still necessary. But good point about greppability, I'll add in the type

[int3]

add reloc types in comments

lld/MachO/InputFiles.cpp

for (const any_relocation_info &anyRel : relInfos) {
     r.pcrel = rel.r_pcrel;
     r.length = rel.r_length;
     uint64_t rawAddend = target->getImplicitAddend(mb, sec, rel);
 
     if (rel.r_extern) {
       r.target = symbols[rel.r_symbolnum];
       r.addend = rawAddend;
     } else {
-      if (!rel.r_pcrel)
-        fatal("TODO: Only pcrel section relocations are supported");
-
       if (rel.r_symbolnum == 0 || rel.r_symbolnum > subsections.size())
         fatal("invalid section index in relocation for offset " +
               std::to_string(r.offset) + " in section " + sec.sectname +
               " of " + getName());
 
       SubsectionMap &targetSubsecMap = subsections[rel.r_symbolnum - 1];
       const section_64 &targetSec = sectionHeaders[rel.r_symbolnum - 1];
+      uint32_t targetOffset;
+      if (rel.r_pcrel)
         // The implicit addend for pcrel section relocations is the pcrel offset
-      // in terms of the addresses in the input file. Here we adjust it so that
-      // it describes the offset from the start of the target section.
-      // TODO: Figure out what to do for non-pcrel section relocations.
+        // in terms of the addresses in the input file. Here we adjust it so
+        // that it describes the offset from the start of the target section.
         // TODO: The offset of 4 is probably not right for ARM64, nor for
         //       relocations with r_length != 2.
-      uint32_t targetOffset =
+        targetOffset =
             sec.addr + rel.r_address + 4 + rawAddend - targetSec.addr;
+      else
+        // The addend for a non-pcrel relocation is its absolute address.
+        targetOffset = rawAddend - targetSec.addr;
       r.target = findContainingSubsection(targetSubsecMap, &targetOffset);
       r.addend = targetOffset;
     }
 
     r.offset = rel.r_address;
     InputSection *subsec = findContainingSubsection(subsecMap, &r.offset);
     subsec->relocs.push_back(r);
   }

lld/test/MachO/relocations.s

 _main:
   callq _f
   mov $0, %rax
   ret
 
 _f:
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
-  leaq _str(%rip), %rsi
+  leaq _str(%rip), %rsi # This generates a pcrel symbol relocation
   mov $21, %rdx # length of str
   syscall
 
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
-  leaq L_.str(%rip), %rsi
+  leaq L_.str(%rip), %rsi # This generates a pcrel section relocation
+  mov $15, %rdx # length of str
+  syscall
+
+  movl $0x2000004, %eax # write() syscall
+  mov $1, %rdi # stdout
+  movq L_.ptr_to_str(%rip), %rsi
   mov $15, %rdx # length of str
   syscall
   ret
 
 .section __TEXT,__cstring
 ## References to this generate a symbol relocation
 _str:
   .asciz "Local defined symbol\n"
 ## References to this generate a section relocation
 L_.str:
   .asciz "Private symbol\n"
+
+.section __DATA,__const
+L_.ptr_to_str:
+## This generates a non-pcrel section relocation
+  .quad L_.str