Re: [linuxsh-dev] Different old_mmap behavior in 2.4.5 and 2.4.8

[David W. <dw...@in...>]

dr...@re... said:
>  Then fix the kernel.  The change is necessary and correct.

I suppose it is feasible for the kernel to accommodate MAP_ANONYMOUS mmap at
the 'wrong' page addresses. Whether it _should_ do that or not sort of 
depends on how good the reasons are for not specifying MAP_FIXED in 
libpthread when you obviously seem to have meant it that way.

I think a combination of mmap(MAP_ANONYMOUS|MAP_SHARED); fork();
mremap(MAP_FIXED) may still get the SH4 to screw up, but I think that was
the case anyway. Mremap seems to be fundamentally broken in that respect - it
doesn't have the same hooks (arch_get_unmapped_area()) that mmap() has to
allow the arch code to vet the addresses use.

I'll leave that one as an exercise for the reader.

Index: arch/sh/kernel/sys_sh.c
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/kernel/sys_sh.c,v
retrieving revision 1.7
diff -u -r1.7 sys_sh.c
--- arch/sh/kernel/sys_sh.c	2001/08/03 23:50:59	1.7
+++ arch/sh/kernel/sys_sh.c	2001/09/11 21:39:00
@@ -68,7 +68,9 @@
 	if (!addr)
 		addr = TASK_UNMAPPED_BASE;
 
-	addr = COLOUR_ALIGN(addr);
+	/* We don't need to do the cache colouring for anonymous pages */
+	if (filp)
+		addr = COLOUR_ALIGN(addr);
 
 	for (vma = find_vma(current->mm, addr); ; vma = vma->vm_next) {
 		/* At this point:  (!vma || addr < vma->vm_end). */
@@ -77,7 +79,8 @@
 		if (!vma || addr + len <= vma->vm_start)
 			return addr;
 		addr = vma->vm_end;
-		addr = COLOUR_ALIGN(addr);
+		if (filp)
+			addr = COLOUR_ALIGN(addr);
 	}
 }
 #endif


--
dwmw2