Bug 137109
| Summary: | compiling with O2 caused a tight loop | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 3 | Reporter: | satish <ksatishv> |
| Component: | gcc3 | Assignee: | Jakub Jelinek <jakub> |
| Status: | CLOSED NOTABUG | QA Contact: | |
| Severity: | medium | Docs Contact: | |
| Priority: | medium | ||
| Version: | 3.0 | ||
| Target Milestone: | --- | ||
| Target Release: | --- | ||
| Hardware: | ia64 | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Bug Fix | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2004-10-25 20:27:19 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
When char is signed (it is on ia64), then your testcase invokes undefined behaviour and what GCC did with it is perfectly fine implementation of undefined behaviour. Integer overflow is defined for unsigned integers only in ISO C. If you compile your program with -O2 -funsigned-char (or change c's type to unsigned char), it will work as you expect. |
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.9) Gecko/20020408 Description of problem: When compiling the following code as gcc -g -O2 a.c -o a Gets stuck in the 'for' loop void pan_generic_mem_set( void *s, int p, int size) { char *temp = (char *) s; while(size > 0) { *temp = p; temp++; size--; } } int main() { char name[10]; char c; pan_generic_mem_set(name,0, sizeof(name)); for (c = (char)1; c!='\0' ; c++) { name[0] = c; name[1] = c; name[2] = c; name[3] = c; } } The assembly listing is somehow missing the cmp4 instruction (gdb) disassemble main Dump of assembler code for function main: 0x4000000000000690 <main+0>: [MMB] alloc r34=ar.pfs,7,4,0 0x4000000000000691 <main+1>: adds r12=-16,r12 0x4000000000000692 <main+2>: nop.b 0x0 0x40000000000006a0 <main+16>: [MFI] mov r32=r1 0x40000000000006a1 <main+17>: nop.f 0x0 0x40000000000006a2 <main+18>: mov r33=b0;; 0x40000000000006b0 <main+32>: [MMB] adds r36=16,r12 0x40000000000006b1 <main+33>: mov r37=r0 0x40000000000006b2 <main+34>: nop.b 0x0 0x40000000000006c0 <main+48>: [MIB] mov r38=10 0x40000000000006c1 <main+49>: mov.i r35=ar.lc 0x40000000000006c2 <main+50>: br.call.sptk.many b0=0x4000000000000640 <pan_generic_mem_set>;; 0x40000000000006d0 <main+64>: [MII] nop.m 0x0 0x40000000000006d1 <main+65>: mov.i ar.lc=-50 0x40000000000006d2 <main+66>: mov r1=r32 0x40000000000006e0 <main+80>: [MMI] mov r37=1;; 0x40000000000006e1 <main+81>: addl r36=72,r1 0x40000000000006e2 <main+82>: nop.i 0x0;; 0x40000000000006f0 <main+96>: [MFB] ld8 r36=[r36] 0x40000000000006f1 <main+97>: nop.f 0x0 0x40000000000006f2 <main+98>: br.call.sptk.many b0=0x4000000000000400 <_init+272>;; 0x4000000000000700 <main+112>: [MMI] nop.m 0x0 0x4000000000000701 <main+113>: mov r1=r32 0x4000000000000702 <main+114>: mov r15=49 0x4000000000000710 <main+128>: [MMI] nop.m 0x0 0x4000000000000711 <main+129>: adds r17=18,r12 0x4000000000000712 <main+130>: adds r16=19,r12;; 0x4000000000000720 <main+144>: [MMB] adds r14=1,r15 0x4000000000000721 <main+145>: st1 [r17]=r15 0x4000000000000722 <main+146>: nop.b 0x0 0x4000000000000730 <main+160>: [MMI] st1 [r16]=r15;; 0x4000000000000731 <main+161>: nop.m 0x0 0x4000000000000732 <main+162>: sxt1 r14=r14;; 0x4000000000000740 <main+176>: [MIB] nop.m 0x0 0x4000000000000741 <main+177>: mov r15=r14 0x4000000000000742 <main+178>: br.cloop.sptk.few 0x4000000000000720 <m ain+144>;; 0x4000000000000750 <main+192>: [MMI] nop.m 0x0 ---Type <return> to continue, or q <return> to quit--- 0x4000000000000751 <main+193>: mov r8=r14 0x4000000000000752 <main+194>: mov.i ar.pfs=r34 0x4000000000000760 <main+208>: [MII] nop.m 0x0 0x4000000000000761 <main+209>: mov.i ar.lc=r35 0x4000000000000762 <main+210>: mov b0=r33 0x4000000000000770 <main+224>: [MMB] nop.m 0x0 0x4000000000000771 <main+225>: adds r12=16,r12 0x4000000000000772 <main+226>: br.ret.sptk.many b0;; End of assembler dump. (gdb) redhat-release/uname Red Hat Enterprise Linux AS release 3 (Taroon Update 3) Linux tower 2.4.21-20.EL #1 SMP Wed Aug 18 20:30:22 EDT 2004 ia64 ia64 ia64 GNU/Linux Version-Release number of selected component (if applicable): How reproducible: Always Steps to Reproduce: 1.Run the attached program 2. 3. Actual Results: The for loop does not break Expected Results: The loop should have broken Additional info: