Re: [Qemu-devel] [PATCH for-4.0 00/17] tcg: Move softmmu out-of-line

[Richard Henderson <richard.henderson@linaro.org>]

On 11/15/18 7:48 PM, Emilio G. Cota wrote:
> - Segfault in code_gen_buffer. This one I don't have a fix for,
>   but it's *much* easier to reproduce when -tb-size is very small,
>   e.g. "-tb-size 5 -smp 2" (BTW it crashes with x86_64 guests too.)
>   So at first I thought the code cache flushing was the problem,
>   but I don't see how that could be, at least from a TCGContext
>   viewpoint -- I agree that clearing the hash table in
>   tcg_region_assign is a good place to do so.

Ho hum.

diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index 639f0b2728..115ea186e5 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -1831,10 +1831,6 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
     existing_tb = tb_link_page(tb, phys_pc, phys_page2);
     /* if the TB already exists, discard what we just translated */
     if (unlikely(existing_tb != tb)) {
-        uintptr_t orig_aligned = (uintptr_t)gen_code_buf;
-
-        orig_aligned -= ROUND_UP(sizeof(*tb), qemu_icache_linesize);
-        atomic_set(&tcg_ctx->code_gen_ptr, (void *)orig_aligned);
         return existing_tb;
     }
     tcg_tb_insert(tb);

We can't easily undo the hash table insert, and for a relatively rare
occurrence it's not worth the effort.


r~