From 9867b30287ec98728e52ed49d03c666e86c90a04 Mon Sep 17 00:00:00 2001 From: Richard Henderson Date: Mon, 22 Aug 2022 18:50:46 -0700 Subject: [PATCH] accel/tcg: Document the faulting lookup in tb_lookup_cmp 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 Signed-off-by: Richard Henderson --- 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; - virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE; + /* + * We know that the first page matched, and an otherwise valid TB + * encountered an incomplete instruction at the end of that page, + * 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 = TARGET_PAGE_ALIGN(desc->pc); phys_page2 = get_page_addr_code(desc->env, virt_page2); if (tb->page_addr[1] == phys_page2) { return true;