Hi!
While working on a vax-linux cross-compiler, I noticed that my vax-linux kernel
won't boot. I tracked this down to a function that re-calculates addresses (VM
addresses to physical addresses for things that run before VM is switched on).
I've then ran the C file through the preprocessor and put it through my host
compiler (gcc-3.3.x on PeeCee). Same result even there.
Testcase:
void *
s0vmaddr_to_load_addr(void *vaddr)
{
extern char _rtext;
return (char *)vaddr - (0x80000000) - 0x00100000 + (unsigned int)
&_rtext;
}
[EMAIL PROTECTED]:~/vax-linux/kernel-2.5$ gcc -c testcase.c
[EMAIL PROTECTED]:~/vax-linux/kernel-2.5$ objdump -d testcase.o
testcase.o: file format elf32-i386
Disassembly of section .text:
00000000 <s0vmaddr_to_load_addr>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: b8 00 00 00 00 mov $0x0,%eax
8: 05 00 00 f0 7f add $0x7ff00000,%eax
d: 03 45 08 add 0x8(%ebp),%eax
10: 5d pop %ebp
11: c3 ret
As you see, four bytes were reserved to be put in by the linker. However, it
seems this is missing in case of a -O2 build:
[EMAIL PROTECTED]:~/vax-linux/kernel-2.5$ gcc -c -O2 testcase.c
[EMAIL PROTECTED]:~/vax-linux/kernel-2.5$ objdump -d testcase.o
testcase.o: file format elf32-i386
Disassembly of section .text:
00000000 <s0vmaddr_to_load_addr>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 8b 45 08 mov 0x8(%ebp),%eax
6: 5d pop %ebp
7: 05 00 00 f0 7f add $0x7ff00000,%eax
c: c3 ret
...or am I wrong here?
Thanks!
Jan-Benedict Glaw <[EMAIL PROTECTED]>
--
Summary: -O2 optimizer bug?
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jbglaw at lug-owl dot de
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21196
