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qemu: fix bug causing BSoD on Windows 98

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Fixes #7342
This commit is contained in:
osy
2025-08-11 20:35:02 -07:00
parent 464fd7dd7c
commit cafa33ecec
1 changed files with 56 additions and 0 deletions
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patches/qemu-10.0.2-utm.patch
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@@ -337,3 +337,59 @@ index 63e10cc6df..1e1b553795 100644
--
2.41.0
From 0f1d6606c28d0ae81a1b311972c5c54e5e867bf0 Mon Sep 17 00:00:00 2001
From: Mark Cave-Ayland <[email protected]>
Date: Wed, 11 Jun 2025 14:03:15 +0100
Subject: [PATCH] target/i386: fix TB exit logic in gen_movl_seg() when writing
to SS
Before commit e54ef98c8a ("target/i386: do not trigger IRQ shadow for LSS"), any
write to SS in gen_movl_seg() would cause a TB exit. The changes introduced by
this commit were intended to restrict the DISAS_EOB_INHIBIT_IRQ exit to the case
where inhibit_irq is true, but missed that a DISAS_EOB_NEXT exit can still be
required when writing to SS and inhibit_irq is false.
Comparing the PE(s) && !VM86(s) section with the logic in x86_update_hflags(), we
can see that the DISAS_EOB_NEXT exit is still required for the !CODE32 case when
writing to SS in gen_movl_seg() because any change to the SS flags can affect
hflags. Similarly we can see that the existing CODE32 case is still correct since
a change to any of DS, ES and SS can affect hflags. Finally for the
gen_op_movl_seg_real() case an explicit TB exit is not needed because the segment
register selector does not affect hflags.
Update the logic in gen_movl_seg() so that a write to SS with inhibit_irq set to
false where PE(s) && !VM86(s) will generate a DISAS_EOB_NEXT exit along with the
inline comment. This has the effect of allowing Win98SE to boot in QEMU once
again.
Signed-off-by: Mark Cave-Ayland <[email protected]>
Fixes: e54ef98c8a ("target/i386: do not trigger IRQ shadow for LSS")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2987
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
---
target/i386/tcg/translate.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 0fcddc2ec0..0cb87d0201 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -2033,8 +2033,11 @@ static void gen_movl_seg(DisasContext *s, X86Seg seg_reg, TCGv src, bool inhibit
tcg_gen_trunc_tl_i32(sel, src);
gen_helper_load_seg(tcg_env, tcg_constant_i32(seg_reg), sel);
- /* For move to DS/ES/SS, the addseg or ss32 flags may change. */
- if (CODE32(s) && seg_reg < R_FS) {
+ /*
+ * For moves to SS, the SS32 flag may change. For CODE32 only, changes
+ * to SS, DS and ES may change the ADDSEG flags.
+ */
+ if (seg_reg == R_SS || (CODE32(s) && seg_reg < R_FS)) {
s->base.is_jmp = DISAS_EOB_NEXT;
}
} else {
--
2.41.0