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linux-user/sh4: restore FP rounding mode on sigreturn

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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>
This commit is contained in:
Matt Turner
2026-05-25 11:26:41 -04:00
committed by Helge Deller
parent 6bf4c0295c
commit a740f17ed0
3 changed files with 15 additions and 2 deletions
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7
linux-user/sh4/signal.c
View File

@@ -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 */

3
target/sh4/cpu.h
View File

@@ -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 */

7
target/sh4/op_helper.c
View File

@@ -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;