Clang error: Cannot compile builtin function

Question

I'm compiling a code which has GCC library extra separately added. While compiling it with clang error

cannot compile

is showing

I've tried added flags. -std=89gnu does not work with a clang. After some inspection found the same function in compiler file.

BUILTIN(__builtin_init_dwarf_reg_size_table, "vv*", "n")

Error:

gcc/unwind-dw2.c:1336:3: error: cannot compile this __builtin_init_dwarf_reg_size_table

Answer 1

That's a really weird error message, can you put the full one here? Also, I'm surprised that you want to compile libgcc with clang, I don't think anyone has really tried before. Some better repro instructions would help though as this seems to work:

echristo@jhereg ~/tmp> cat foo.c

char x[16]; void a() { __builtin_init_dwarf_reg_size_table(x); }

echristo@jhereg ~/tmp> clang -S -o - foo.c --target=x86_64-linux-gnu

    .text
    .file   "foo.c"
    .globl  a                       # -- Begin function a
    .p2align    4, 0x90
    .type   a,@function
a:                                      # @a
    .cfi_startproc
# %bb.0:
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset %rbp, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register %rbp
    movb    $8, x
    movb    $8, x+1
    movb    $8, x+2
    movb    $8, x+3
    movb    $8, x+4
    movb    $8, x+5
    movb    $8, x+6
    movb    $8, x+7
    movb    $8, x+8
    movb    $8, x+9
    movb    $8, x+10
    movb    $8, x+11
    movb    $8, x+12
    movb    $8, x+13
    movb    $8, x+14
    movb    $8, x+15
    movb    $8, x+16
    popq    %rbp
    .cfi_def_cfa %rsp, 8
    retq
.Lfunc_end0:
    .size   a, .Lfunc_end0-a
    .cfi_endproc
                                        # -- End function
    .type   x,@object               # @x
    .comm   x,16,16

    .ident  "clang version 9.0.0 (https://github.com/llvm/llvm-project.git b669fea42f5c2a5b203c3f0da2a6b04b90bfd5a7)"
    .section    ".note.GNU-stack","",@progbits
    .addrsig
    .addrsig_sym x