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accel/tcg: Document the faulting lookup in tb_lookup_cmp

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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>
This commit is contained in:
Richard Henderson 2022-08-22 18:50:46 -07:00
parent 7e0d9973ea
commit 9867b30287
1 changed files with 10 additions and 1 deletions
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11
accel/tcg/cpu-exec.c
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@ -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;