Fix the `nop` opcode on some MIPS-based Loongson CPUs.

After much trouble building Mono in Debian/MIPS, @directhex
narrowed it down to this issue:

https://sourceware.org/ml/binutils/2009-11/msg00387.html

So since some of the 2E and 2F versions of the Loongson CPUs
break with a regular `sll zero, zero, 0` we need to issue an
`or at, at, 0`. This makes sure we don't randomly deadlock or
blow up when the CPU is under heavy load.

Yes, really.

diff --git a/mono/arch/mips/mips-codegen.h b/mono/arch/mips/mips-codegen.h
index dc4df7d8a6a048ffe35419d5975e09a63528e98c..1dbd1c6e279d40613c8d7ccf9eb3ea0664528993 100644 (file)
--- a/mono/arch/mips/mips-codegen.h
+++ b/mono/arch/mips/mips-codegen.h
@@ -334,7 +334,7 @@ enum {
 /* misc and coprocessor ops */
 #define mips_move(c,dest,src) mips_addu(c,dest,src,mips_zero)
 #define mips_dmove(c,dest,src) mips_daddu(c,dest,src,mips_zero)
-#define mips_nop(c) mips_sll(c,0,0,0)
+#define mips_nop(c) mips_or(c,mips_at,mips_at,0)
 #define mips_break(c,code) mips_emit32(c, ((code)<<6)|13)
 #define mips_mfhi(c,dest) mips_format_r(c,0,0,0,dest,0,16)
 #define mips_mflo(c,dest) mips_format_r(c,0,0,0,dest,0,18)