LLD is not assigning an OutputSection of type OVERLAY an address.

[smithp35]

Bugzilla Link	42006
Version	unspecified
OS	Linux
CC	@smithp35

Extended Description

When attempting to test Thunk reuse between two OVERLAY OutputSections which we shouldn't do as only one will be in memory at a time I came across a relocation out of range error as Thunks were not created at all. On further inspection the LMA and VMA expressions were all ignored with 0 being the result.

I think that this is due to the requirement of OVERLAY to clear the SHF_ALLOC flag on the OutputSection. This seems to prevent Thunk Creation and causes the LMA and VMA to be ignored.

cat overlay.s
.section .sec1, "ax", %progbits
bl far

      .section .sec2, "ax", %progbits
      bl far

      .section .sec3, "ax", %progbits
      .globl far
      .type far, %function

far: bx lr

cat overlay.lds
SECTIONS {
.sec1 0x1000 (OVERLAY) : AT (0x1000) { *(.sec1) }
.sec2 0x1000 (OVERLAY) : AT (0x2000) { *(.sec2) }
.far 0x10000000 : { *(.sec3) }
}

llvm-mc --triple=armv7-a-linux-gnueabihf overlay.s -filetype=obj -o overlay.o
ld.lld overlay.o --script overlay.lds
ld.lld: error: overlay.o:(.sec1+0x0): relocation R_ARM_CALL out of range: 268435448 is not in [-33554432, 33554431]
ld.lld: error: overlay.o:(.sec2+0x0): relocation R_ARM_CALL out of range: 268435448 is not in [-33554432, 33554431]

cat overlay2.lds
SECTIONS {
.sec1 0x1000 (OVERLAY) : AT (0x1000) { *(.sec1) }
.sec2 0x1000 (OVERLAY) : AT (0x2000) { *(.sec2) }
.far 0x3000 : { *(.sec3) }
}
ld.lld overlay.o --script overlay2.lds -o overlay --print-map
VMA LMA Size Align Out In Symbol
0 0 4 1 .sec1
0 0 4 1 overlay.o:(.sec1)
0 0 0 1 $a.0
0 0 4 1 .sec2
0 0 4 1 overlay.o:(.sec2)
0 0 0 1 $a.1
0 0 7a 1 .comment
0 0 7a 1 :(.comment)
0 0 50 4 .symtab
0 0 50 4 :(.symtab)
0 0 3b 1 .shstrtab
0 0 3b 1 :(.shstrtab)
0 0 14 1 .strtab
0 0 14 1 :(.strtab)
3000 3000 4 1 .far
3000 3000 4 1 overlay.o:(.sec3)
3000 3000 0 1 $a.2
3000 3000 0 1 far
3004 3004 0 4 .text
3004 3004 0 4 overlay.o:(.text)

This is in contrast with arm-linux-gnueabihf-ld.bfd
LOAD overlay.o

.sec1 0x0000000000001000 0x10
*(.sec1)
.sec1 0x0000000000001000 0x4 overlay.o
fill 0x0000000000001004 0x4
.sec1.__stub 0x0000000000001008 0x8 linker stubs

.sec2 0x0000000000001000 0x10 load address 0x0000000000002000
*(.sec2)
.sec2 0x0000000000001000 0x4 overlay.o
fill 0x0000000000001004 0x4
.sec2.__stub 0x0000000000001008 0x8 linker stubs

.far 0x0000000010000000 0x4 load address 0x0000000010001000
*(.sec3)
.sec3 0x0000000010000000 0x4 overlay.o
0x0000000010000000 far

Note that ld.bfd has removed the SHF_ALLOC after assigning addresses and has created stubs (thunks) in each overlay as we would expect.

In summary I think:
-LLD should not hard-code the address of a non-alloc section to 0.
-LLD should permit thunks to be generated from OVERLAY regions.
-LLD should prohibit thunks from being shared with an OVERLAY region.