Commit 6e6c4efe authored by Richard Henderson's avatar Richard Henderson
Browse files

tcg: Restart after TB code generation overflow 

If a TB generates too much code, try again with fewer insns.

Fixes: https://bugs.launchpad.net/bugs/1824853


Reviewed-by: default avatarPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: default avatarRichard Henderson <richard.henderson@linaro.org>
parent 8b86d6d2

accel/tcg/translate-all.c

+32 −6
Original line number Diff line number Diff line
@@ -1722,6 +1722,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu, 
    tb->cflags = cflags;

    tb->trace_vcpu_dstate = *cpu->trace_dstate;

    tcg_ctx->tb_cflags = cflags;

 tb_overflow:



#ifdef CONFIG_PROFILER

    /* includes aborted translations because of exceptions */
@@ -1755,14 +1756,39 @@ TranslationBlock *tb_gen_code(CPUState *cpu, 
    ti = profile_getclock();

#endif



    /* ??? Overflow could be handled better here.  In particular, we

       don't need to re-do gen_intermediate_code, nor should we re-do

       the tcg optimization currently hidden inside tcg_gen_code.  All

       that should be required is to flush the TBs, allocate a new TB,

       re-initialize it per above, and re-do the actual code generation.  */

    gen_code_size = tcg_gen_code(tcg_ctx, tb);

    if (unlikely(gen_code_size < 0)) {

        switch (gen_code_size) {

        case -1:

            /*

             * Overflow of code_gen_buffer, or the current slice of it.

             *

             * TODO: We don't need to re-do gen_intermediate_code, nor

             * should we re-do the tcg optimization currently hidden

             * inside tcg_gen_code.  All that should be required is to

             * flush the TBs, allocate a new TB, re-initialize it per

             * above, and re-do the actual code generation.

             */

            goto buffer_overflow;



        case -2:

            /*

             * The code generated for the TranslationBlock is too large.

             * The maximum size allowed by the unwind info is 64k.

             * There may be stricter constraints from relocations

             * in the tcg backend.

             *

             * Try again with half as many insns as we attempted this time.

             * If a single insn overflows, there's a bug somewhere...

             */

            max_insns = tb->icount;

            assert(max_insns > 1);

            max_insns /= 2;

            goto tb_overflow;



        default:

            g_assert_not_reached();

        }

    }

    search_size = encode_search(tb, (void *)gen_code_buf + gen_code_size);

    if (unlikely(search_size < 0)) {

tcg/tcg.c

+4 −0
Original line number Diff line number Diff line
@@ -3996,6 +3996,10 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb) 
        if (unlikely((void *)s->code_ptr > s->code_gen_highwater)) {

            return -1;

        }

        /* Test for TB overflow, as seen by gen_insn_end_off.  */

        if (unlikely(tcg_current_code_size(s) > UINT16_MAX)) {

            return -2;

        }

    }

    tcg_debug_assert(num_insns >= 0);

    s->gen_insn_end_off[num_insns] = tcg_current_code_size(s);