This cppreference example fails with Error: invalid operands (*UND* and *UND* sections) for %'` on g++ 11.1.0 on my Archlinux box, but not on coliru. Why?
The file name is _1h6.cpp:
$ g++ _1h6.cpp -S && as _1h6.s # same error as g++ _1h6.cpp
_1h6.s: Assembler messages:
_1h6.s:11: Error: invalid operands (*UND* and *UND* sections) for `%'
_1h6.cpp:29: Error: invalid operands (*UND* and *UND* sections) for `%'
_1h6.cpp:30: Error: invalid operands (*UND* and *UND* sections) for `%'
Here the C++ code:
#include <iostream>
extern "C" int func();
// the definition of func is written in assembly language
// raw string literal could be very useful
asm(R"(
.globl func
.type func, @function
func:
.cfi_startproc
movl $7, %eax
ret
.cfi_endproc
)");
int main()
{
int n = func();
// extended inline assembly
asm ("leal (%0,%0,4),%0"
: "=r" (n)
: "0" (n));
std::cout << "7*5 = " << n << std::endl; // flush is intentional
// standard inline assembly
asm ("movq $60, %rax\n\t" // the exit syscall number on Linux
"movq $2, %rdi\n\t" // this program returns 2
"syscall");
}
UND refers to a temporary elf section (undefined) for references without target. Could my g++ internally link different libraries than coliru? I use the same command as coliru:
g++ -std=c++20 -pthread -O2 -Wall -Wextra -pedantic -pthread -pedantic-errors _1h6.cpp -lm -latomic -lstdc++fs && ./a.out
When I use -S to create the assembly, the error happens with as _1h6.s.
Here the -S output:
.file "_1h6.cpp"
.text
.local _ZStL8__ioinit
.comm _ZStL8__ioinit,1,1
#APP
.globl func
.type func, @function
func:
.cfi_startproc
movl $7, %eax
ret
.cfi_endproc
.section .rodata
.LC0:
.string "7*5 = "
#NO_APP
.text
.globl main
.type main, @function
main:
.LFB1729:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $16, %rsp
call func@PLT
movl %eax, -4(%rbp)
movl -4(%rbp), %eax
#APP
# 27 "_1h6.cpp" 1
leal (%eax,%eax,4),%eax
# 0 "" 2
#NO_APP
movl %eax, -4(%rbp)
leaq .LC0(%rip), %rax
movq %rax, %rsi
leaq _ZSt4cout(%rip), %rax
movq %rax, %rdi
call _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@PLT
movq %rax, %rdx
movl -4(%rbp), %eax
movl %eax, %esi
movq %rdx, %rdi
call _ZNSolsEi@PLT
movq _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GOTPCREL(%rip), %rdx
movq %rdx, %rsi
movq %rax, %rdi
call _ZNSolsEPFRSoS_E@PLT
#APP
# 32 "_1h6.cpp" 1
movq $60, %rax
movq $2, %rdi
syscall
# 0 "" 2
#NO_APP
movl $0, %eax
leave
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE1729:
.size main, .-main
.type _Z41__static_initialization_and_destruction_0ii, @function
_Z41__static_initialization_and_destruction_0ii:
.LFB2232:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $16, %rsp
movl %edi, -4(%rbp)
movl %esi, -8(%rbp)
cmpl $1, -4(%rbp)
jne .L5
cmpl $65535, -8(%rbp)
jne .L5
leaq _ZStL8__ioinit(%rip), %rax
movq %rax, %rdi
call _ZNSt8ios_base4InitC1Ev@PLT
leaq __dso_handle(%rip), %rax
movq %rax, %rdx
leaq _ZStL8__ioinit(%rip), %rax
movq %rax, %rsi
movq _ZNSt8ios_base4InitD1Ev@GOTPCREL(%rip), %rax
movq %rax, %rdi
call __cxa_atexit@PLT
.L5:
nop
leave
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE2232:
.size _Z41__static_initialization_and_destruction_0ii, .-_Z41__static_initialization_and_destruction_0ii
.type _GLOBAL__sub_I_main, @function
_GLOBAL__sub_I_main:
.LFB2233:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
movl $65535, %esi
movl $1, %edi
call _Z41__static_initialization_and_destruction_0ii
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE2233:
.size _GLOBAL__sub_I_main, .-_GLOBAL__sub_I_main
.section .init_array,"aw"
.align 8
.quad _GLOBAL__sub_I_main
.hidden __dso_handle
.ident "GCC: (GNU) 11.1.0"
.section .note.GNU-stack,"",@progbits
As the error comes from as, it is a binutils problem.
as --version:
GNU assembler (GNU Binutils) 2.36.1
Copyright (C) 2021 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or later.
This program has absolutely no warranty.
This assembler was configured for a target of `x86_64-pc-linux-gnu'.
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