[Bug c++/90886] New: loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886
Bug ID: 90886
Summary: loop/while/for problem
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: joe at freakyacres dot com
Target Milestone: ---
I apologize because this all got a little bit above my head. But the following
code only runs the "for" loop once.
volatile unsigned char x;
int main() {
while (1) {
for (unsigned char i = 0 ; i < 128 ; i++) {
x = i;
}
}
}
Apparently compiles to...
$ avr-g++ -Os -mmcu=atmega328p main.cpp -o main.elf
$ avr-objdump --demangle -d main.elf
(other code omitted)
0090 :
90: 10 92 00 01 sts 0x0100, r1 ; 0x800100 <_edata>
0094 <_exit>:
94: f8 94 cli
0096 <__stop_program>:
96: ff cf rjmp.-2 ; 0x96 <__stop_program>
$ avr-g++ --version
Replacing the for loop 128 with any other value fixes the problem.
Much work was done at the github link below where minds much more advanced than
my own researched and confirmed what was happening.
https://github.com/arduino/Arduino/issues/8973
https://forum.arduino.cc/index.php?topic=621017.0
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886 --- Comment #2 from Joe --- Using built-in specs. Reading specs from /usr/lib/gcc/avr/5.4.0/device-specs/specs-avr2 COLLECT_GCC=avr-gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/avr/5.4.0/lto-wrapper Target: avr Configured with: ../gcc/configure -v --enable-languages=c,c++ --prefix=/usr/lib --infodir=/usr/share/info --mandir=/usr/share/man --bindir=/usr/bin --libexecdir=/usr/lib --libdir=/usr/lib --enable-shared --with-system-zlib --enable-long-long --enable-nls --without-included-gettext --disable-libssp --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=avr CFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong -Wformat ' CPPFLAGS='-Wdate-time -D_FORTIFY_SOURCE=2' CXXFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong -Wformat ' FCFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong' FFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong' GCJFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong' LDFLAGS='-Wl,-Bsymbolic-functions -Wl,-z,relro' OBJCFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong -Wformat ' OBJCXXFLAGS='-g -O2 -fdebug-prefix-map=/build/gcc-avr-n0nSsH/gcc-avr-5.4.0+Atmel3.6.0=. -fstack-protector-strong -Wformat ' Thread model: single gcc version 5.4.0 (GCC)
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886
--- Comment #3 from Joe ---
Changing i to 127 produces following assembly...
volatile unsigned char x;
int main() {
while (1) {
for (unsigned char i = 0 ; i < 127 ; i++) {
x = i;
}
}
}
0090 :
90: 80 e0 ldi r24, 0x00 ; 0
92: 80 93 00 01 sts 0x0100, r24 ; 0x800100 <_edata>
96: 8f 5f subir24, 0xFF ; 255
98: 8f 37 cpi r24, 0x7F ; 127
9a: d1 f3 breq.-12; 0x90
9c: fa cf rjmp.-12; 0x92
009e <_exit>:
9e: f8 94 cli
00a0 <__stop_program>:
a0: ff cf rjmp.-2 ; 0xa0 <__stop_program>
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886 Joe changed: What|Removed |Added Version|5.4.0 |7.3.0 --- Comment #5 from Joe --- Tested with 7.3.0 with same results. Using built-in specs. Reading specs from /home/xxx/avr-tools-test/avr/bin/../lib/gcc/avr/7.3.0/device-specs/specs-avr2 COLLECT_GCC=./avr-g++ COLLECT_LTO_WRAPPER=/home/xxx/avr-tools-test/avr/bin/../libexec/gcc/avr/7.3.0/lto-wrapper Target: avr Configured with: ../gcc/configure --enable-fixed-point --enable-languages=c,c++ --prefix=/home/jenkins/workspace/avr-gcc-staging/label/debian7-x86_64/objdir --disable-nls --disable-libssp --disable-libada --disable-shared --with-avrlibc=yes --with-dwarf2 --disable-doc --target=avr Thread model: single gcc version 7.3.0 (GCC)
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886 --- Comment #6 from Joe --- Hmmm... Maybe 7.3.0 isn't supported either.
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886 Joe changed: What|Removed |Added Version|7.3.0 |7.4.0 --- Comment #8 from Joe --- Here is assembler under 7.4.0... Segmentation fault with i=128. Any other value within the bounds of unsigned char is ok. i=128 04f0 : 4f0: c6 05 1a 0b 20 00 00movb $0x0,0x200b1a(%rip)# 201011 4f7: 66 0f 1f 84 00 00 00nopw 0x0(%rax,%rax,1) 4fe: 00 00 i=129 04f0 : 4f0: 31 c0 xor%eax,%eax 4f2: 88 05 19 0b 20 00 mov%al,0x200b19(%rip)# 201011 4f8: ff c0 inc%eax 4fa: 3c 81 cmp$0x81,%al 4fc: 75 f4 jne4f2 4fe: eb f0 jmp4f0
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886 --- Comment #9 from Joe --- Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.4.0-1ubuntu1~18.04.1' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
[Bug target/90886] loop/while/for problem
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90886 --- Comment #10 from Joe --- probably noticed but code is always "i <" not "i =" as I stated in the previous comments.
