inline-asm/10035: arm register r0 is corrupted

inline-asm/10035: arm register r0 is corrupted

[murphychen]

>Number:         10035
>Category:       inline-asm
>Synopsis:       arm register r0 is corrupted
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Mar 12 06:36:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     gcc-3.0
>Release:        unknown-1.0
>Organization:
>Environment:
linux
>Description:
When assigning local variable to use arm register r0, the initialization of the local variable will be ignored.
>How-To-Repeat:
compile the c code again.
>Fix:
Don't know how to fix.
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="gccbug.txt"
Content-Disposition: inline; filename="gccbug.txt"

$cat test.c

int fun(char *s, long n) {
  register long a asm("r0");
  a = 3;
  fun("xxx", a);
  a = 5;
  return a;
}

$ arm-linux-gcc -Os -S -mthumb -mcpu=arm7tdmi -mtune=arm7tdmi -march=armv4t test.c 

$ cat test.s

@ Generated by gcc 3.0 for ARM/elf
        .file   "test.c"
        .code   16
        .section        .rodata
        .align  2
.LC0:
        .ascii  "xxx\000"
        .text
        .align  2
        .global fun
        .thumb_func
        .type   fun,function
fun:
        push    {lr}
        ldr     r0, .L3
        mov     r1, r0
        bl      fun
        mov     r0, #5
        pop     {pc}
.L4:
        .align  2
.L3:
        .word   .LC0
.Lfe1:
        .size   fun,.Lfe1-fun
        .ident  "GCC: (GNU) 3.0"

$ arm-linux-gcc -v -Os -S -mthumb -mcpu=arm7tdmi -mtune=arm7tdmi -march=armv4t test.c 
Reading specs from /usr/local/arm/3.0/lib/gcc-lib/arm-linux/3.0/specs
Configured with: ../../src/gcc-3.0/configure --target=arm-linux --prefix=/usr/local/arm/3.0 --enable-languages=c,c++,objc,f77,java --enable-threads
Thread model: posix
gcc version 3.0
 /usr/local/arm/3.0/lib/gcc-lib/arm-linux/3.0/cc1 -lang-c -v -D__GNUC__=3 -D__GNUC_MINOR__=0 -D__GNUC_PATCHLEVEL__=0 -Dunix -Dlinux -D__ELF__ -D__unix__ -D__linux__ -D__ELF__ -D__unix -D__linux -Asystem=unix -Asystem=posix -Acpu=arm -Amachine=arm -D__CHAR_UNSIGNED__ -D__OPTIMIZE_SIZE__ -D__OPTIMIZE__ -D__STDC_HOSTED__=1 -D__ARM_ARCH_4T__ -D__APCS_32__ -D__ARMEL__ -D__THUMBEL__ -D__thumb__ test.c -quiet -dumpbase test.c -mthumb -mcpu=arm7tdmi -mtune=arm7tdmi -march=armv4t -Os -version -o test.s
GNU CPP version 3.0 (cpplib) (ARM GNU/Linux with ELF)
GNU C version 3.0 (arm-linux)
        compiled by GNU C version 2.95.2 20000220 (Debian GNU/Linux).
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/arm/3.0/lib/gcc-lib/arm-linux/3.0/include
 /usr/local/arm/3.0/arm-linux/sys-include
 /usr/local/arm/3.0/arm-linux/include
End of search list.

Re: inline-asm/10035: arm register r0 is corrupted

[rearnsha]

Synopsis: arm register r0 is corrupted

State-Changed-From-To: open->closed
State-Changed-By: rearnsha
State-Changed-When: Wed Mar 12 11:58:05 2003
State-Changed-Why:
    Register r0 is reserved by the ABI for passing arguments to functions and for returning results from those functions.  You can't reserve it for your own variable.  In general, you must restrict fixed register allocations to registers that don't have specific purposes in the ABI.  For ARM this is the set r4-r8 (and in some circumstances you may also use r9 and r10).

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10035