| Message ID | 20220823220542.1993395-14-richard.henderson@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | linux-user: Fix siginfo_t contents when jumping to non-readable pages | expand |
On Tue, 2022-08-23 at 15:05 -0700, Richard Henderson wrote: > 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. > > 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; > > - 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; Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
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;
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. Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- accel/tcg/cpu-exec.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)