[Qemu-devel] [PATCH] alpha ldl_l stl_c fix

[Vince Weaver]

Hello

The following patch is needed for a hello world binary to run under 
alpha-linux-user.

The issue is the ldl_l and stl_c instructions.  The current implementation 
is a bit confused.
   ldl_l should set the lock bit, and write the address to a table
   stl_c should write to memory only if lock bit is set, then return the
         lock_bit, then reset the lock_bit to zero

The current code does a weird mix of these things that don't seem to work.

This patch fixes things enough for me for hello_world to work, but it 
still isn't correct if we ever want to use these instructions to implement 
atomic loads/stores or run multithreaded code.

Note... the patch includes a commented out branch.  For proper emulation 
that branch should be included, but for some reason on my x86_64 system if 
the branch is included, then the memory address calculation is converted 
to nops for some reason (leading to a segfault).  I'm not sure why that is 
happening.

Vince

Index: target-alpha/translate.c
===================================================================
--- target-alpha/translate.c    (revision 5643)
+++ target-alpha/translate.c    (working copy)
@@ -138,13 +138,13 @@

 static always_inline void gen_qemu_ldl_l (TCGv t0, TCGv t1, int flags)
 {
-    tcg_gen_mov_i64(cpu_lock, t1);
+    tcg_gen_movi_i64(cpu_lock, 1);
     tcg_gen_qemu_ld32s(t0, t1, flags);
 }

 static always_inline void gen_qemu_ldq_l (TCGv t0, TCGv t1, int flags)
 {
-    tcg_gen_mov_i64(cpu_lock, t1);
+    tcg_gen_movi_i64(cpu_lock, 1);
     tcg_gen_qemu_ld64(t0, t1, flags);
 }

@@ -201,34 +201,27 @@

 static always_inline void gen_qemu_stl_c (TCGv t0, TCGv t1, int flags)
 {
-    int l1, l2;
+    int l1;

     l1 = gen_new_label();
-    l2 = gen_new_label();
-    tcg_gen_brcond_i64(TCG_COND_NE, cpu_lock, t1, l1);
+//    tcg_gen_brcondi_i64(TCG_COND_EQ, cpu_lock, 0, l1);
     tcg_gen_qemu_st32(t0, t1, flags);
-    tcg_gen_movi_i64(t0, 0);
-    tcg_gen_br(l2);
     gen_set_label(l1);
-    tcg_gen_movi_i64(t0, 1);
-    gen_set_label(l2);
-    tcg_gen_movi_i64(cpu_lock, -1);
+    tcg_gen_mov_i64(t0, cpu_lock); 
+    tcg_gen_movi_i64(cpu_lock, 0);
+
 }

 static always_inline void gen_qemu_stq_c (TCGv t0, TCGv t1, int flags)
 {
-    int l1, l2;
+    int l1;

     l1 = gen_new_label();
-    l2 = gen_new_label();
-    tcg_gen_brcond_i64(TCG_COND_NE, cpu_lock, t1, l1);
+//    tcg_gen_brcondi_i64(TCG_COND_EQ, cpu_lock, 0, l1);
     tcg_gen_qemu_st64(t0, t1, flags);
-    tcg_gen_movi_i64(t0, 0);
-    tcg_gen_br(l2);
     gen_set_label(l1);
-    tcg_gen_movi_i64(t0, 1);
-    gen_set_label(l2);
-    tcg_gen_movi_i64(cpu_lock, -1);
+    tcg_gen_movi_i64(t0, cpu_lock);
+    tcg_gen_movi_i64(cpu_lock, 0);
 }

 static always_inline void gen_store_mem (DisasContext *ctx,