threads and gc on SPARC/Solaris 2.8

Tue Aug 7 14:53:00 GMT 2001

On 2001年6月27日, Boehm, Hans wrote:
> The trunk has a bug, as does my version. GC_clear_stack_inner is called,
> but not defined for SPARC + threads. It looks to me like removing the /* &&
> !defined(THREADS) */ condition in mach_dep.c should fix the problem. I
> think that was only a space optimization, which is now no longer correct.
> I'll apply that fix to my version, but I'd appreciate it if someone with a
> less modified tree could test it and check it in sooner than I will.

It looks like nobody has fixed this on the trunk yet.
I tried Hans's suggestion... gctest aborts on an "Illegal Instruction"
trap. That may explain why the code was conditionalized in the first
place.
The faulting address is consistently the top of a VM page. Wild
conjecture: GC_clear_stack_inner is entering a guard page, and the kernel
handles the page fault. On attempting to emulate the store (can
SPARC not restart the faulting instruction?) the kernel doesn't recognize
the instruction format with a global register.
The following seems to work. Does it look reasonable? I really don't
know SPARC very well.
Index: mach_dep.c
===================================================================
RCS file: /cvs/gcc/gcc/boehm-gc/mach_dep.c,v
retrieving revision 1.8
diff -u -r1.8 mach_dep.c

--- mach_dep.c 2001年05月21日 08:35:13 1.8
+++ mach_dep.c 2001年08月07日 21:34:58
@@ -511,7 +511,7 @@
 /* returns arg. Stack clearing is crucial on SPARC, so we supply */
 /* an assembly version that's more careful. Assumes limit is hotter */
 /* than sp, and limit is 8 byte aligned. */
-#if defined(ASM_CLEAR_CODE) && !defined(THREADS)
+#if defined(ASM_CLEAR_CODE)
 #ifndef SPARC
 --> fix it
 #endif
@@ -540,6 +540,8 @@
 #else
 asm("mov %sp,%o2"); /* Save sp */
 asm("add %sp,-8,%o3"); /* p = sp-8 */
+ asm("st %o1,[%o1]"); /* force stack growth if needed */
+ asm("and %o3,-8,%o3"); /* force doubleword alignment */
 asm("clr %g1"); /* [g0,g1] = 0 */
 asm("add %o1,-0x60,%sp"); /* Move sp out of the way, */
 /* so that traps still work. */
