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Re: [Qemu-devel] [PATCH] ARM - Remove fixed map code buffer restriction
From: |
andrzej zaborowski |
Subject: |
Re: [Qemu-devel] [PATCH] ARM - Remove fixed map code buffer restriction |
Date: |
Mon, 12 Dec 2011 18:24:14 +0100 |
Hi,
On 12 December 2011 16:55, Peter Maydell <address@hidden> wrote:
> On 12 December 2011 15:37, Dr. David Alan Gilbert
> <address@hidden> wrote:
>> On ARM, don't map the code buffer at a fixed location, and fix up the
>> call/goto tcg routines to let it do long jumps.
>>
>> Mapping the code buffer at a fixed address could sometimes result in it being
>> mapped over the top of the heap with pretty random results.
>>
>> This diff is against v1.0.
>
> Patches should always be against master, although we're still
> close enough to 1.0 that this will probably apply anyway.
>
> Comments like "This diff is against v1.0." go below the '---' so they
> don't appear in the final commit log.
>
> Code generally looks OK to me.
To me as well, I'll apply if there are no objections. I remember
Peter asked about MAP_FIXED on other hosts, has there been a
resolution?
>
>> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>> ---
>> exec.c | 4 +---
>> tcg/arm/tcg-target.c | 31 ++++++++++++-------------------
>> 2 files changed, 13 insertions(+), 22 deletions(-)
>>
>> diff --git a/exec.c b/exec.c
>> index 6b92198..ef83da1 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -497,9 +497,7 @@ static void code_gen_alloc(unsigned long tb_size)
>> if (code_gen_buffer_size > (512 * 1024 * 1024))
>> code_gen_buffer_size = (512 * 1024 * 1024);
>> #elif defined(__arm__)
>> - /* Map the buffer below 32M, so we can use direct calls and
>> branches */
>> - flags |= MAP_FIXED;
>> - start = (void *) 0x01000000UL;
>> + /* Keep the buffer no bigger than 16GB to branch between blocks */
>> if (code_gen_buffer_size > 16 * 1024 * 1024)
>> code_gen_buffer_size = 16 * 1024 * 1024;
>> #elif defined(__s390x__)
>> diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
>> index e05a64f..730d913 100644
>> --- a/tcg/arm/tcg-target.c
>> +++ b/tcg/arm/tcg-target.c
>> @@ -842,6 +842,12 @@ static inline void tcg_out_st8(TCGContext *s, int cond,
>> tcg_out_st8_12(s, cond, rd, rn, offset);
>> }
>>
>> +/* The _goto case is normally between TBs within the same code buffer,
>> + and with the code buffer limited to 16GB we shouldn't need the long
>> + case.
>> +
>> + .... except to the prologue that is in its own buffer.
>> + */
>> static inline void tcg_out_goto(TCGContext *s, int cond, uint32_t addr)
>> {
>> int32_t val;
>> @@ -855,22 +861,20 @@ static inline void tcg_out_goto(TCGContext *s, int
>> cond, uint32_t addr)
>> if (val - 8 < 0x01fffffd && val - 8 > -0x01fffffd)
>> tcg_out_b(s, cond, val);
>> else {
>> -#if 1
>> - tcg_abort();
>> -#else
>> if (cond == COND_AL) {
>> tcg_out_ld32_12(s, COND_AL, TCG_REG_PC, TCG_REG_PC, -4);
>> - tcg_out32(s, addr); /* XXX: This is l->u.value, can we use it?
>> */
>> + tcg_out32(s, addr);
>
> I see these XXXs have been there since the ARM tcg target was
> introduced. Does anybody know what they were referring to? Andrzej?
David asked me about them, but I couldn't figure it out. (the part in
tcg_out_call apparently is just copy&pasted from tcg_ouy_goto)
BTW: I think we can also use the "ld" branch when we see the goto
target is in Thumb mode.
Cheers
Re: [Qemu-devel] [PATCH] ARM - Remove fixed map code buffer restriction, andrzej zaborowski, 2011/12/14