[PULL 05/12] linux-user/sh4: restore FP rounding mode on sigreturn

[Helge Deller <deller@kernel.org>]

From: Matt Turner <mattst88@gmail.com>

The SH4 FPSCR rounding-mode (RM) and denormal (DN) bits are not held
only in env->fpscr: they are also reflected into the derived
env->fp_status via set_float_rounding_mode()/set_flush_to_zero(). The
guest keeps the two in sync by routing every write to FPSCR through
helper_ld_fpscr().

restore_sigcontext() wrote the saved value straight into env->fpscr and
never touched env->fp_status, so on sigreturn the interrupted code
resumed with whatever FP rounding mode and flush-to-zero setting the
signal handler last installed. (regs->flags = 0 forces the FR/SZ/PR TB
flags to be recomputed, but fp_status is runtime float state, not a TB
flag, so it was left stale.) This is the FP analogue of the T/M/Q bit
problem just fixed for the integer status register.

Factor the FPSCR -> fp_status synchronisation out of helper_ld_fpscr()
into cpu_load_fpscr() and use it from restore_sigcontext() so the
rounding mode round-trips correctly across signal delivery.

Fixes: c3b5bc8ab3 ("SH4: Signal handling for the user space emulator, by Magnus Damm.")
Cc: qemu-stable@nongnu.org
Reviewed-by: Yoshinori Sato <yoshinori.sato@nifty.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
---
 linux-user/sh4/signal.c | 7 ++++++-
 target/sh4/cpu.h        | 3 +++
 target/sh4/op_helper.c  | 7 ++++++-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/linux-user/sh4/signal.c b/linux-user/sh4/signal.c
index cc36425c49..00290d6e40 100644
--- a/linux-user/sh4/signal.c
+++ b/linux-user/sh4/signal.c
@@ -173,7 +173,12 @@ static void restore_sigcontext(CPUSH4State *regs, struct target_sigcontext *sc)
     for (i=0; i<16; i++) {
         __get_user(regs->fregs[i], &sc->sc_fpregs[i]);
     }
-    __get_user(regs->fpscr, &sc->sc_fpscr);
+    /* Resync the derived float_status state, not just env->fpscr. */
+    {
+        uint32_t fpscr;
+        __get_user(fpscr, &sc->sc_fpscr);
+        cpu_load_fpscr(regs, fpscr);
+    }
     __get_user(regs->fpul, &sc->sc_fpul);
 
     regs->tra = -1;         /* disable syscall checks */
diff --git a/target/sh4/cpu.h b/target/sh4/cpu.h
index 4b0f3f6d97..3302702376 100644
--- a/target/sh4/cpu.h
+++ b/target/sh4/cpu.h
@@ -379,4 +379,7 @@ static inline void cpu_write_sr(CPUSH4State *env, uint32_t sr)
     env->sr = sr & ~((1u << SR_M) | (1u << SR_Q) | (1u << SR_T));
 }
 
+/* Set FPSCR and the derived float_status rounding/flush-to-zero state. */
+void cpu_load_fpscr(CPUSH4State *env, uint32_t val);
+
 #endif /* SH4_CPU_H */
diff --git a/target/sh4/op_helper.c b/target/sh4/op_helper.c
index 669bc84cb6..cf0f80e4a5 100644
--- a/target/sh4/op_helper.c
+++ b/target/sh4/op_helper.c
@@ -204,7 +204,7 @@ void helper_macw(CPUSH4State *env, int32_t arg0, int32_t arg1)
     }
 }
 
-void helper_ld_fpscr(CPUSH4State *env, uint32_t val)
+void cpu_load_fpscr(CPUSH4State *env, uint32_t val)
 {
     env->fpscr = val & FPSCR_MASK;
     if ((val & FPSCR_RM_MASK) == FPSCR_RM_ZERO) {
@@ -215,6 +215,11 @@ void helper_ld_fpscr(CPUSH4State *env, uint32_t val)
     set_flush_to_zero((val & FPSCR_DN) != 0, &env->fp_status);
 }
 
+void helper_ld_fpscr(CPUSH4State *env, uint32_t val)
+{
+    cpu_load_fpscr(env, val);
+}
+
 static void update_fpscr(CPUSH4State *env, uintptr_t retaddr)
 {
     int xcpt, cause, enable;
-- 
2.54.0