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authorSergey Fedorov <serge.fdrv@gmail.com>2016-04-08 19:48:12 +0300
committerRichard Henderson <rth@twiddle.net>2016-05-12 14:06:41 -1000
commit5b053a4a28278bca606eeff7d1c0730df1b047e9 (patch)
treee9567828b03440c0d228edfc0aef296dafb34800 /cpu-exec.c
parentf9c5b66f487a04d3747dc6997b1503f9258df945 (diff)
downloadqemu-arm-5b053a4a28278bca606eeff7d1c0730df1b047e9.tar.gz
tcg: Clean up direct block chaining safety checks
We don't take care of direct jumps when address mapping changes. Thus we must be sure to generate direct jumps so that they always keep valid even if address mapping changes. Luckily, we can only allow to execute a TB if it was generated from the pages which match with current mapping. Document tcg_gen_goto_tb() declaration and note the reason for destination PC limitations. Some targets with variable length instructions allow TB to straddle a page boundary. However, we make sure that both of TB pages match the current address mapping when looking up TBs. So it is safe to do direct jumps into the both pages. Correct the checks for some of those targets. Given that, we can safely patch a TB which spans two pages. Remove the unnecessary check in cpu_exec() and allow such TBs to be patched. Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Richard Henderson <rth@twiddle.net>
Diffstat (limited to 'cpu-exec.c')
-rw-r--r--cpu-exec.c7
1 files changed, 2 insertions, 5 deletions
diff --git a/cpu-exec.c b/cpu-exec.c
index debc65ca69..f984dc71cb 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -508,11 +508,8 @@ int cpu_exec(CPUState *cpu)
next_tb = 0;
tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
}
- /* see if we can patch the calling TB. When the TB
- spans two pages, we cannot safely do a direct
- jump. */
- if (next_tb != 0 && tb->page_addr[1] == -1
- && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
+ /* See if we can patch the calling TB. */
+ if (next_tb != 0 && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
tb_add_jump((TranslationBlock *)(next_tb & ~TB_EXIT_MASK),
next_tb & TB_EXIT_MASK, tb);
}