And for fun, try the quiz at http://blog.regehr.org/archives/721. Then cry as you realize how much broken code there must be out there...
> -----Original Message----- > From: Michiel Konstapel [mailto:m.konsta...@sownet.nl] > Sent: Friday, February 15, 2013 09:31 > To: Rick Kimball; mspgcc-users@lists.sourceforge.net > Subject: Re: [Mspgcc-users] msp430-gcc 4.6.3 optimizer killing my code > > Signed overflow is actually undefined behaviour in C/C++, and the > compiler is free to do whatever it wants in that case. For gcc, there's > a flag to make signed integer arithmetic wrap around, though: > > -fwrapv > This option instructs the compiler to assume that signed > arithmetic overflow of > addition, subtraction and multiplication wraps around using twos- > complement > representation. This flag enables some optimizations and disables > others. > > It's one of the "safety switches" I've enabled for our embedded code, > because it's something many people (including myself until recently) > don't know about. Especially if you're coming from Java, where signed > overflow *is* defined to wrap. > > John Regehr has a large amount of interesting, if scary, information > about undefined behaviour in C on his blog, for example > http://blog.regehr.org/archives/759 and > http://blog.regehr.org/archives/761. > > HTH, > Michiel > > > -----Original Message----- > > From: Rick Kimball [mailto:rick.kimb...@gmail.com] > > Sent: Friday, February 15, 2013 03:19 > > To: mspgcc-users@lists.sourceforge.net > > Subject: [Mspgcc-users] msp430-gcc 4.6.3 optimizer killing my code > > > > I've been working on some C++ template based classes and ran into a > > snag. At first I thought it was related to the C++ templates however > > it turns out when I reduced the code down to a straight 'C' > > implementation I still have the same problem. > > > > The code below has issues with the int8_t data type. In "test 2" i8 > > starts at 126 and incrementing it should make it roll over to a > > negative number but it doesn't. This problem appears when i use -Os ( > > which is my normal mode of operation ) and does go away if I back off > > and use -O1. If nothing else it would interesting if others try this > > with their version of the compiler. I'm using the linux version that > > ships with Energia: > > gcc version 4.6.3 20120301 (mspgcc LTS 20120406 unpatched) (MSPGCC > > 20120406 (With patches: sf3540953 sf3559978)) Adding volatile to just > > the int8_t declaration will get rid of the problem. > > > > If you use msp430-gcc you might try this code and post your results. > > > > Secondary question, red-hat has been churning away with the msp430- > gcc > > code for a while. Is there an ETA for when we might see a new version > > from them? > > > > Thanks, > > > > -rick > > > > code on github: https://gist.github.com/RickKimball/4957969 > > > > /** > > * signedtest.c - this fails to output int8_t values properly when > > optimized with -Os > > * > > * Compiled like this: > > * > > * $ msp430-gcc -mmcu=msp430g2553 -DF_CPU=16000000 -Os -Wall \ > > * -Wno-main -g -mdisable-watchdog -fdata-sections -ffunction- > > sections \ > > * -Wl,--gc-sections signedtest.c > > * > > * $ mspdebug rf2500 "prog a.out" > > * > > * compiling with -O1 produces proper output, as does changing the > > * int8_t to volatile int8_t > > * > > */ > > > > #include <msp430.h> > > #include <stdint.h> > > #include <stdlib.h> > > > > /** > > * serial output routines > > */ > > void printc(const char c) { > > while(!(IFG2 & UCA0TXIFG)); > > IFG2 &= ~UCA0TXIFG; > > UCA0TXBUF = c; > > } > > > > void prints(const char *s) { > > while(*s) > > printc(*s++); > > } > > > > void printi(int8_t i) { > > char buff[8]; > > > > #if 1 > > if ( i < 0 ) { > > printc('-'); > > i=-i; > > } > > utoa((i & 0xff),buff,10); > > #else > > itoa((int8_t)i,buff,10); /* also tried this, also failed */ > > #endif > > > > prints(buff); > > } > > > > void printu(uint8_t i) { > > char buff[8]; > > > > utoa((i & 0xff),buff,10); > > prints(buff); > > } > > > > void println() { > > printc('\n'); > > } > > > > static const uint32_t brd = (F_CPU + (9600 >> 1)) / 9600; // Bit rate > > divisor > > > > int main(void) { > > uint16_t indx; > > > > #define BAD > > > > #if defined(GOOD) > > volatile int8_t i8; // test2 produces valid results > > #elif defined(BAD) > > int8_t i8; // broken for test2 unless marked volatile or you use - > O1 > > #endif > > uint8_t u8; > > > > WDTCTL = WDTPW + WDTHOLD; // No watchdog > reset > > // > > DCOCTL = 0; // Run at 16 MHz > > BCSCTL1 = CALBC1_16MHZ; // > > DCOCTL = CALDCO_16MHZ; // > > > > //P1DIR |= BIT0 | BIT4; P1SEL |= BIT4; > > > > // GPIO Configuration ; // Set alternate > > function I/O for UART & SPI > > P1SEL |= BIT2; // UART P1.2(tx) > > P1SEL2 |= BIT2; > > > > // Serial Config > > UCA0CTL1 = UCSWRST; // Hold USCI in > > reset to allow configuration > > UCA0CTL0 = 0; // No parity, LSB > > first, 8 bits, one stop bit, UART (async) > > UCA0BR1 = (brd >> 12) & 0xFF; // High byte of > whole > > divisor > > UCA0BR0 = (brd >> 4) & 0xFF; // Low byte of > whole > > divisor > > UCA0MCTL = ((brd << 4) & 0xF0) | UCOS16; // Fractional > > divisor, oversampling mode > > UCA0CTL1 = UCSSEL_2; // Use SMCLK for > bit > > rate generator, release reset > > > > > > prints("-test 1- int8_t=125, uint8_t=125 - signed/unsigned boundary > > rollover\n RESULTS: always succeeds\n"); > > i8=125; u8=125; > > for(indx=0; indx < 5; indx++, i8++, u8++) { > > printi(i8); > > prints(", "); > > printu(u8); > > println(); > > } > > > > prints("-test 2- int8_t=126, uint8_t=126 - signed/unsigned boundary > > rollover\n RESULTS: fails unless volatile\n"); > > i8=126; u8=126; > > for(indx=0; indx < 4; indx++, i8++, u8++) { > > printi(i8); > > prints(", "); > > printu(u8); > > println(); > > } > > > > prints("-test 3- int8_t=127, uint8_t=127 - signed/unsigned boundary > > rollover\n RESULTS: always ok\n"); > > i8=127; u8=127; > > for(indx=0; indx < 3; indx++, i8++, u8++) { > > printi(i8); > > prints(", "); > > printu(u8); > > println(); > > } > > > > while(1); > > } > > > > #if 0 > > >>> Bad results when int8_t not volatile > > > > -test 1- int8_t=125, uint8_t=125 - signed/unsigned boundary > rollover > > RESULTS: always succeeds > > 125, 125 > > 126, 126 > > 127, 127 > > -128, 128 > > -127, 129 > > -test 2- int8_t=126, uint8_t=126 - signed/unsigned boundary > rollover > > RESULTS: fails unless volatile > > 126, 126 > > 127, 127 > > 127, 128 << fail this is the wrong result > > 127, 129 << fail this is the wrong result > > -test 3- int8_t=127, uint8_t=127 - signed/unsigned boundary > rollover > > RESULTS: always ok > > 127, 127 > > -128, 128 > > -127, 129 > > > > > > >>> Good results when using volatile int8_t > > > > -test 1- int8_t=125, uint8_t=125 - signed/unsigned boundary > rollover > > RESULTS: always succeeds > > 125, 125 > > 126, 126 > > 127, 127 > > -128, 128 > > -127, 129 > > -test 2- int8_t=126, uint8_t=126 - signed/unsigned boundary > rollover > > RESULTS: fails unless volatile > > 126, 126 > > 127, 127 > > -128, 128 > > -127, 129 > > -test 3- int8_t=127, uint8_t=127 - signed/unsigned boundary > rollover > > RESULTS: always ok > > 127, 127 > > -128, 128 > > -127, 129 > > > > > > #endif > > > > --------------------------------------------------------------------- > -- > > ------- > > Free Next-Gen Firewall Hardware Offer > > Buy your Sophos next-gen firewall before the end March 2013 > > and get the hardware for free! Learn more. > > http://p.sf.net/sfu/sophos-d2d-feb > > _______________________________________________ > > Mspgcc-users mailing list > > Mspgcc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/mspgcc-users > > ----------------------------------------------------------------------- > ------- > Free Next-Gen Firewall Hardware Offer > Buy your Sophos next-gen firewall before the end March 2013 > and get the hardware for free! Learn more. > http://p.sf.net/sfu/sophos-d2d-feb > _______________________________________________ > Mspgcc-users mailing list > Mspgcc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/mspgcc-users ------------------------------------------------------------------------------ Free Next-Gen Firewall Hardware Offer Buy your Sophos next-gen firewall before the end March 2013 and get the hardware for free! Learn more. http://p.sf.net/sfu/sophos-d2d-feb _______________________________________________ Mspgcc-users mailing list Mspgcc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mspgcc-users
