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From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Subject: [PULL 13/20] accel/tcg: Document the faulting lookup in tb_lookup_cmp
Date: Thu, 1 Sep 2022 07:52:03 +0100
Message-Id: <20220901065210.117081-18-richard.henderson@linaro.org>
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It was non-obvious to me why we can raise an exception in
the middle of a comparison function, but it works.
While nearby, use TARGET_PAGE_ALIGN instead of open-coding.
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
accel/tcg/cpu-exec.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 7887af6f45..5f43b9769a 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -198,7 +198,16 @@ static bool tb_lookup_cmp(const void *p, const void *d)
tb_page_addr_t phys_page2;
target_ulong virt_page2;
=20
- virt_page2 =3D (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZ=
E;
+ /*
+ * We know that the first page matched, and an otherwise valid=
TB
+ * encountered an incomplete instruction at the end of that pa=
ge,
+ * therefore we know that generating a new TB from the current=
PC
+ * must also require reading from the next page -- even if the
+ * second pages do not match, and therefore the resulting insn
+ * is different for the new TB. Therefore any exception raised
+ * here by the faulting lookup is not premature.
+ */
+ virt_page2 =3D TARGET_PAGE_ALIGN(desc->pc);
phys_page2 =3D get_page_addr_code(desc->env, virt_page2);
if (tb->page_addr[1] =3D=3D phys_page2) {
return true;
--=20
2.34.1