Package: gcc-6
Version: 6.3.0-18+deb9u
GCC produces incorrect code for the following program. The C11 standard
requires (§ F.8.5) that the floating point exception flag is set by the
following code, yet the generated assembly does not set it. These
results are for an x86-64 system running Debian 9.
The interaction is:
“““
$ gcc -W -Wall -S -std=c11 -O3 -march=native -masm=intel -fverbose-asm
test.c
test.c:2:0: warning: ignoring #pragma STDC FENV_ACCESS [-Wunknown-pragmas]
#pragma STDC FENV_ACCESS ON
test.c: In function ‘main’:
test.c:11:9: warning: unused variable ‘x’ [-Wunused-variable]
float x = 0.0 / 0.0;
^
”””
The file “test.c” is:
“““
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
#if !defined(__STDC_IEC_559__)
#error "Requires IEC 60559 compliance"
#endif
int f();
int main(void) {
float x = 0.0 / 0.0;
f();
return 0;
}
”””
The output file “test.s” is (excluding comments) is:
“““
.section .rodata.str1.1,"aMS",@progbits,1
.LC0:
.string "Hello world!"
.section .text.startup,"ax",@progbits
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB5:
.cfi_startproc
sub rsp, 8 #,
.cfi_def_cfa_offset 16
xor eax, eax #
call f@PLT #
lea rdi, .LC0[rip] #,
xor eax, eax #
call printf@PLT #
xor eax, eax #
add rsp, 8 #,
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE5:
.size main, .-main
.ident "GCC: (Debian 6.3.0-18+deb9u1) 6.3.0 20170516"
.section .note.GNU-stack,"",@progbits
”””
