Package: gcc Version: 1:2.95.2-13 Severity: normal To add to my problem (reported on debian devel) here is a test program to reproduce it:
Output with o=2 (unaligned) [EMAIL PROTECTED]:~$ ./bla Start of struct 0xeffffc70, content: a=aaaaaaaaaaaaaa rel-pos x=12 offset o=2 Now we are going to memcpy dst=a+x+o=0xeffffc7e result of a+x+o access: b=aaaabbbbbbbbbb Now we are going to bcopy dst=&(tmp_iphdr->saddr)=0xeffffc7e result of bcopy &(tmp_iphdr->saddr) access: b=aaaabbbbbbbbbb Now we are going to memcpy dst=&(tmp_iphdr->saddr)=0xeffffc7e Bus error Output with o=4 (aligned) [EMAIL PROTECTED]:~$ gcc -O2 -o bla bla.c [EMAIL PROTECTED]:~$ ./bla Start of struct 0xeffffc70, content: a=aaaaaaaaaaaaaa rel-pos x=12 offset o=4 Now we are going to memcpy dst=a+x+o=0xeffffc80 result of a+x+o access: b=aaaabbbbbbbbbb Now we are going to bcopy dst=&(tmp_iphdr->saddr)=0xeffffc80 result of bcopy &(tmp_iphdr->saddr) access: b=aaaabbbbbbbbbb Now we are going to memcpy dst=&(tmp_iphdr->saddr)=0xeffffc80 result of memcpy &(tmp_iphdr->saddr) access: b=aaaabbbbbbbbbb Note: in both cases the pointer to the target (of bcopy and memcpy) are the same a+x+o=0xeffffc7e and &(tmp_iphdr->saddr)=0xeffffc7e. The first case works with memcpy, the second doesnt. This looks clearly like some broken optimization. Indeed: [EMAIL PROTECTED]:~$ gcc -O0 -o bla bla.c [EMAIL PROTECTED]:~$ ./bla Start of struct 0xeffffc70, content: a=aaaaaaaaaaaaaa rel-pos x=12 offset o=2 Now we are going to memcpy dst=a+x+o=0xeffffc7e result of a+x+o access: b=aaaabbbbbbbbbb Now we are going to bcopy dst=&(tmp_iphdr->saddr)=0xeffffc7e result of bcopy &(tmp_iphdr->saddr) access: b=aaaabbbbbbbbbb Now we are going to memcpy dst=&(tmp_iphdr->saddr)=0xeffffc7e result of memcpy &(tmp_iphdr->saddr) access: b=aaaabbbbbbbbbb I guess this means I should report a bug against gcc -- System Information Debian Release: 2.2 Kernel Version: Linux auric 2.4.15-pre4 #1 SMP Thu Nov 15 09:26:46 EST 2001 sparc64 unknown Versions of the packages gcc depends on: ii binutils 2.10.0.9-4 The GNU assembler, linker and binary utiliti ii cpp 2.95.2-13 The GNU C preprocessor. ii libc6 2.1.3-20 GNU C Library: Shared libraries and Timezone
