error: relocation R_MOS_PCREL_8 out of range: -134 is not in [-128, 127] about llvm-mos

[mysterymath]

Wow, okay, we (I) gloriously misinterpreted the semantics of TargetInstrInfo::getInstSizeInBytes(). We summarily return 3, since that's the max instruction size on our supported targets. But "instruction" in this case includes things like the INLINEASM "instruction", and all of the other targets include a call to TII.getInlineAsmLength() to handle that case.

Should be straightforward to fix, but I'll need to write a test case and scan the other targets' implementations to see if there's anything else we missed.

[juj]

Built latest llvm-mos from git source to see if the issue persists with latest compiler, which it seems to:

C:\code\EDIT\recvprg>mos-c64-clang++ br.cpp -Oz -o br.prg
ld.lld: error: lto.tmp:(function main: .text.main+0x84): relocation R_MOS_PCREL_8 out of range: -130 is not in [-128, 127]; references section '.text.main'
>>> referenced by ld-temp.o

ld.lld: error: lto.tmp:(function main: .text.main+0x88): relocation R_MOS_PCREL_8 out of range: -134 is not in [-128, 127]; references section '.text.main'
>>> referenced by ld-temp.o
mos-clang++: error: ld.lld command failed with exit code 1 (use -v to see invocation)

C:\code\EDIT\recvprg>mos-c64-clang++ --version
clang version 18.0.0 (https://github.com/llvm-mos/llvm-mos.git bc9be3b91539473a3fc566a58b6a8236793b7dfc)
Target: mos
Thread model: posix
InstalledDir: C:\code\llvm-mos\build\bin
Configuration file: C:\code\llvm-mos\build\bin\mos-c64.cfg

[mysterymath]

I'll be debugging this one "out loud" on this bug, I'm trying something new :)

Running the linker with -Wl,--save-temps produces the LTO temporary object file that the linker is failing to relocate.

Examining that with llvm-readelf --all yields the following relocations for .text.main:

Relocation section '.rela.text.main' at offset 0x2364 contains 4 entries:
 Offset     Info    Type                Sym. Value  Symbol's Name + Addend
00000001  00000203 R_MOS_ADDR16           00000000   .text.main + 79
00000084  00000206 R_MOS_PCREL_8          00000000   .text.main + 3
00000088  00000206 R_MOS_PCREL_8          00000000   .text.main + 3
0000008a  00000203 R_MOS_ADDR16           00000000   .text.main + 53

Accordingly, at offset 0x84, there's a branch to offset 0x3, which is definitely out of range.
Using llvm-objdump -d reveals that the branch is the one at the end of the following asm:

00000079 <end2>:
      79: ae 09 de      ldx     $de09                   ; 0xde09 <end2+0xdd90>
      7c: ac 08 de      ldy     $de08                   ; 0xde08 <end2+0xdd8f>
      7f: a9 01         lda     #$1
      81: e0 00         cpx     #$0
      83: d0 00         bne     $85 <end2+0xc>

Getting a symbolic assembly dump using -Wl,--lto-emit-asm yields:

end2:

        ;NO_APP
.LBB0_3:                                ; =>This Inner Loop Header: Depth=1
        ldx     56841
        ldy     56840
        lda     #1
        cpx     #0
        bne     .LBB0_1

Notably, this code is outside of the inline assembly, so it seems likely that it is mis-sizing the inline assembly somehow, since the far branch to .LBB0_1 doesn't get replaced with an inverse branch that skips an absolute JMP.