Hi.
While qemu's behaviour matches what one would expect from reading
the docs, it does not match what I'm seeing on h/w.
Can anyone else confirm what the correct behaviour is here?
---
The syscall and sysret instructions behave a bit differently:
TF is checked after the instruction completes.
This allows the o/s to disable #DB at a syscall by adding TF to FMASK.
And then when the sysret is executed the #DB is taken "as if" the
syscall insn just completed.
Signed-off-by: Doug Evans <d...@google.com>
---
target-i386/bpt_helper.c | 12 ++++++++++++
target-i386/helper.h | 1 +
target-i386/translate.c | 29 ++++++++++++++++++++++++-----
3 files changed, 37 insertions(+), 5 deletions(-)
diff --git a/target-i386/bpt_helper.c b/target-i386/bpt_helper.c
index 6fd7fe0..d771461 100644
--- a/target-i386/bpt_helper.c
+++ b/target-i386/bpt_helper.c
@@ -244,6 +244,18 @@ void helper_single_step(CPUX86State *env)
raise_exception(env, EXCP01_DB);
}
+void helper_rechecking_single_step(CPUX86State *env)
+{
+ if ((env->eflags & TF_MASK) != 0)
+ {
+#ifndef CONFIG_USER_ONLY
+ check_hw_breakpoints(env, true);
+ env->dr[6] |= DR6_BS;
+#endif
+ raise_exception(env, EXCP01_DB);
+ }
+}
+
void helper_set_dr(CPUX86State *env, int reg, target_ulong t0)
{
#ifndef CONFIG_USER_ONLY
diff --git a/target-i386/helper.h b/target-i386/helper.h
index 4e859eb..bd9b2cf 100644
--- a/target-i386/helper.h
+++ b/target-i386/helper.h
@@ -79,6 +79,7 @@ DEF_HELPER_2(cmpxchg16b_unlocked, void, env, tl)
DEF_HELPER_2(cmpxchg16b, void, env, tl)
#endif
DEF_HELPER_1(single_step, void, env)
+DEF_HELPER_1(rechecking_single_step, void, env)
DEF_HELPER_1(cpuid, void, env)
DEF_HELPER_1(rdtsc, void, env)
DEF_HELPER_1(rdtscp, void, env)
diff --git a/target-i386/translate.c b/target-i386/translate.c
index 9fd1a04..42d036e 100644
--- a/target-i386/translate.c
+++ b/target-i386/translate.c
@@ -2500,8 +2500,10 @@ static void gen_bnd_jmp(DisasContext *s)
}
/* Generate an end of block. Trace exception is also generated if needed.
- If IIM, set HF_INHIBIT_IRQ_MASK if it isn't already set. */
-static void gen_eob_inhibit_irq(DisasContext *s, bool inhibit)
+ If INHIBIT, set HF_INHIBIT_IRQ_MASK if it isn't already set.
+ If RECHECK_TF, emit a rechecking helper for #DB, ignoring the state of
+ S->TF. This is used by the syscall/sysret insns. */
+static void gen_eob_worker(DisasContext *s, bool inhibit, bool recheck_tf)
{
gen_update_cc_op(s);
@@ -2517,6 +2519,9 @@ static void gen_eob_inhibit_irq(DisasContext *s, bool
inhibit)
}
if (s->singlestep_enabled) {
gen_helper_debug(cpu_env);
+ } else if (recheck_tf) {
+ gen_helper_rechecking_single_step(cpu_env);
+ tcg_gen_exit_tb(0);
} else if (s->tf) {
gen_helper_single_step(cpu_env);
} else {
@@ -2525,10 +2530,17 @@ static void gen_eob_inhibit_irq(DisasContext *s,
bool inhibit)
s->is_jmp = DISAS_TB_JUMP;
}
+/* End of block.
+ If INHIBIT, set HF_INHIBIT_IRQ_MASK if it isn't already set. */
+static void gen_eob_inhibit_irq(DisasContext *s, bool inhibit)
+{
+ gen_eob_worker(s, inhibit, false);
+}
+
/* End of block, resetting the inhibit irq flag. */
static void gen_eob(DisasContext *s)
{
- gen_eob_inhibit_irq(s, false);
+ gen_eob_worker(s, false, false);
}
/* generate a jump to eip. No segment change must happen before as a
@@ -7108,7 +7120,10 @@ static target_ulong disas_insn(CPUX86State *env,
DisasContext *s,
if (s->lma) {
set_cc_op(s, CC_OP_EFLAGS);
}
- gen_eob(s);
+ /* TF handling for the syscall insn is different. The TF bit is
checked
+ after the syscall insn completes. This allows #DB to not be
+ generated after one has entered CPL0 if TF is set in FMASK. */
+ gen_eob_worker(s, false, true);
break;
case 0x107: /* sysret */
if (!s->pe) {
@@ -7119,7 +7134,11 @@ static target_ulong disas_insn(CPUX86State *env,
DisasContext *s,
if (s->lma) {
set_cc_op(s, CC_OP_EFLAGS);
}
- gen_eob(s);
+ /* TF handling for the sysret insn is different. The TF bit is
+ checked after the sysret insn completes. This allows #DB to
be
+ generated "as if" the syscall insn in userspace has just
+ completed. */
+ gen_eob_worker(s, false, true);
}
break;
#endif
--
2.8.0.rc3.226.g39d4020
