[Qemu-devel] [PATCH] tcp/mips: Change TCG_AREG0 (fp -> s0)

[Stefan Weil]

Register fp (frame pointer) is a bad choice for compilations
without optimisation, because the compiler makes heavy use
of this register (so the resulting code crashes).

Register s0 was used for TCG_AREG1 in earlier releases,
but was no longer used and is now free for TCG_AREG0.

The resulting code works for compilations without
optimisation (tested with qemu mips in qemu mips
on x86 host).

v2:

* Remove s0 from tcg_target_callee_save_regs and add fp there.
  Hint from Aurelien Jarno, thanks.

* Add fp to list of reserved registers.

Cc: Aurelien Jarno <aurel...@aurel32.net>
Signed-off-by: Stefan Weil <w...@mail.berlios.de>
---
 dyngen-exec.h         |    2 +-
 tcg/mips/tcg-target.c |    6 ++++--
 tcg/mips/tcg-target.h |    2 +-
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/dyngen-exec.h b/dyngen-exec.h
index b9f6969..85a2616 100644
--- a/dyngen-exec.h
+++ b/dyngen-exec.h
@@ -61,7 +61,7 @@ extern int printf(const char *, ...);
 #elif defined(__hppa__)
 #define AREG0 "r17"
 #elif defined(__mips__)
-#define AREG0 "fp"
+#define AREG0 "s0"
 #elif defined(__sparc__)
 #ifdef CONFIG_SOLARIS
 #define AREG0 "g2"
diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
index f4fb615..c9094ee 100644
--- a/tcg/mips/tcg-target.c
+++ b/tcg/mips/tcg-target.c
@@ -1450,7 +1450,9 @@ static const TCGTargetOpDef mips_op_defs[] = {
 };
 
 static int tcg_target_callee_save_regs[] = {
+#if 0 /* used for the global env (TCG_AREG0), so no need to save */
     TCG_REG_S0,
+#endif
     TCG_REG_S1,
     TCG_REG_S2,
     TCG_REG_S3,
@@ -1459,8 +1461,7 @@ static int tcg_target_callee_save_regs[] = {
     TCG_REG_S6,
     TCG_REG_S7,
     TCG_REG_GP,
-    /* TCG_REG_FP, */ /* currently used for the global env, so np
-                         need to save */
+    TCG_REG_FP,
     TCG_REG_RA,       /* should be last for ABI compliance */
 };
 
@@ -1524,6 +1525,7 @@ void tcg_target_init(TCGContext *s)
     tcg_regset_set_reg(s->reserved_regs, TCG_REG_AT);   /* internal use */
     tcg_regset_set_reg(s->reserved_regs, TCG_REG_T0);   /* internal use */
     tcg_regset_set_reg(s->reserved_regs, TCG_REG_RA);   /* return address */
+    tcg_regset_set_reg(s->reserved_regs, TCG_REG_FP);   /* frame pointer */
     tcg_regset_set_reg(s->reserved_regs, TCG_REG_SP);   /* stack pointer */
 
     tcg_add_target_add_op_defs(mips_op_defs);
diff --git a/tcg/mips/tcg-target.h b/tcg/mips/tcg-target.h
index 0292d33..0028bfa 100644
--- a/tcg/mips/tcg-target.h
+++ b/tcg/mips/tcg-target.h
@@ -97,7 +97,7 @@ enum {
 #undef TCG_TARGET_HAS_ext16u_i32   /* andi rt, rs, 0xffff */
 
 /* Note: must be synced with dyngen-exec.h */
-#define TCG_AREG0 TCG_REG_FP
+#define TCG_AREG0 TCG_REG_S0
 
 /* guest base is supported */
 #define TCG_TARGET_HAS_GUEST_BASE
-- 
1.7.0