[Qemu-devel] [PATCH] tci: Fix build with no '-DNDEBUG'

[Qemu-devel] [PATCH] tci: Fix build with no '-DNDEBUG'

[Sergey Fedorov]

From: Sergey Fedorov <serge.fdrv@gmail.com>

assert() always evaluates its argument so there's no need to #ifdef the
definitions which is only used for assert(). Actually, doing so
generates a compilation warning which is treated as an error in QEMU
build by default. Let compiler sort out and eliminate unnecessary
local variables.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
---
 tci.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/tci.c b/tci.c
index 7cbb39ed4b6a..d709e008f3f9 100644
--- a/tci.c
+++ b/tci.c
@@ -472,10 +472,8 @@ uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
 
     for (;;) {
         TCGOpcode opc = tb_ptr[0];
-#if !defined(NDEBUG)
         uint8_t op_size = tb_ptr[1];
         uint8_t *old_code_ptr = tb_ptr;
-#endif
         tcg_target_ulong t0;
         tcg_target_ulong t1;
         tcg_target_ulong t2;
-- 
2.7.3

Re: [Qemu-devel] [PATCH] tci: Fix build with no '-DNDEBUG'

[Stefan Weil]

Am 04.04.2016 um 13:05 schrieb Sergey Fedorov:
> From: Sergey Fedorov <serge.fdrv@gmail.com>
>
> assert() always evaluates its argument so there's no need to #ifdef the
> definitions which is only used for assert(). Actually, doing so
> generates a compilation warning which is treated as an error in QEMU
> build by default. Let compiler sort out and eliminate unnecessary
> local variables.
>
> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
> ---
>  tci.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/tci.c b/tci.c
> index 7cbb39ed4b6a..d709e008f3f9 100644
> --- a/tci.c
> +++ b/tci.c
> @@ -472,10 +472,8 @@ uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
>  
>      for (;;) {
>          TCGOpcode opc = tb_ptr[0];
> -#if !defined(NDEBUG)
>          uint8_t op_size = tb_ptr[1];
>          uint8_t *old_code_ptr = tb_ptr;
> -#endif
>          tcg_target_ulong t0;
>          tcg_target_ulong t1;
>          tcg_target_ulong t2;


This patch should not be applied.

>From the Linux man page for assert: "the macro assert() generates no code".

Which variant of the assert macro evaluates its argument even when NDEBUG
is defined? On which system with which configuration did you see the
problem?

There is indeed a regression in the current code. Commit
d38ea87ac54af64ef611de434d07c12dc0399216 added an include statement
which includes assert.h before NDEBUG is defined. This is wrong and
needs a fix. Could you please try tci.c starting like this?

/* Defining NDEBUG disables assertions (which makes the code faster). */
#if !defined(CONFIG_DEBUG_TCG) && !defined(NDEBUG)
# define NDEBUG
#endif

#include "qemu/osdep.h"

Thanks,
Stefan

Re: [Qemu-devel] [PATCH] tci: Fix build with no '-DNDEBUG'

[Sergey Fedorov]

On 04/04/16 14:56, Stefan Weil wrote:
> Am 04.04.2016 um 13:05 schrieb Sergey Fedorov:
>> From: Sergey Fedorov <serge.fdrv@gmail.com>
>>
>> assert() always evaluates its argument so there's no need to #ifdef the
>> definitions which is only used for assert(). Actually, doing so
>> generates a compilation warning which is treated as an error in QEMU
>> build by default. Let compiler sort out and eliminate unnecessary
>> local variables.
>>
>> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
>> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
>> ---
>>  tci.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/tci.c b/tci.c
>> index 7cbb39ed4b6a..d709e008f3f9 100644
>> --- a/tci.c
>> +++ b/tci.c
>> @@ -472,10 +472,8 @@ uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
>>  
>>      for (;;) {
>>          TCGOpcode opc = tb_ptr[0];
>> -#if !defined(NDEBUG)
>>          uint8_t op_size = tb_ptr[1];
>>          uint8_t *old_code_ptr = tb_ptr;
>> -#endif
>>          tcg_target_ulong t0;
>>          tcg_target_ulong t1;
>>          tcg_target_ulong t2;
>
> This patch should not be applied.

Oops, you're right, it's a really silly patch.

>
> From the Linux man page for assert: "the macro assert() generates no code".
>
> Which variant of the assert macro evaluates its argument even when NDEBUG
> is defined? 

I'm not sure of how I got this misunderstanding :)

> On which system with which configuration did you see the
> problem?

I get the following error messages when I compile on Ubuntu 14.04.4 LTS.

$ /home/sergey/projects/qemu/configure
--target-list=x86_64-linux-user,x86_64-softmmu --enable-tcg-interpreter
$ make
...
/home/sergey/projects/qemu/tci.c: In function ‘tcg_qemu_tb_exec’:
/home/sergey/projects/qemu/tci.c:528:25: error: ‘old_code_ptr’
undeclared (first use in this function)
             assert(tb_ptr == old_code_ptr + op_size);
                         ^
/home/sergey/projects/qemu/tci.c:528:25: note: each undeclared
identifier is reported only once for each function it appears in
/home/sergey/projects/qemu/tci.c:528:40: error: ‘op_size’ undeclared
(first use in this function)
             assert(tb_ptr == old_code_ptr + op_size);
                                        ^
make[1]: *** [tci.o] Error 1

>
> There is indeed a regression in the current code. Commit
> d38ea87ac54af64ef611de434d07c12dc0399216 added an include statement
> which includes assert.h before NDEBUG is defined. This is wrong and
> needs a fix. Could you please try tci.c starting like this?
>
> /* Defining NDEBUG disables assertions (which makes the code faster). */
> #if !defined(CONFIG_DEBUG_TCG) && !defined(NDEBUG)
> # define NDEBUG
> #endif
>
> #include "qemu/osdep.h"
>

Doing so really helps. So what are the plans of how to fix the problem?

Thanks,
Sergey

Re: [Qemu-devel] [PATCH] tci: Fix build with no '-DNDEBUG'

[Stefan Weil]

Am 04.04.2016 um 15:22 schrieb Sergey Fedorov:
> On 04/04/16 14:56, Stefan Weil wrote:
[...]
>> There is indeed a regression in the current code. Commit
>> d38ea87ac54af64ef611de434d07c12dc0399216 added an include statement
>> which includes assert.h before NDEBUG is defined. This is wrong and
>> needs a fix. Could you please try tci.c starting like this?
>>
>> /* Defining NDEBUG disables assertions (which makes the code faster). */
>> #if !defined(CONFIG_DEBUG_TCG) && !defined(NDEBUG)
>> # define NDEBUG
>> #endif
>>
>> #include "qemu/osdep.h"
>>
> 
> Doing so really helps. So what are the plans of how to fix the problem?
> 
> Thanks,
> Sergey


The correct fix needs a little bit more code because my first try (see
above) did not get the definition of macro CONFIG_DEBUG_TCG.

My patch was now sent to the list.

Regards,
Stefan

Re: [Qemu-devel] [PATCH] tci: Fix build with no '-DNDEBUG'

[Sergey Fedorov]

On 04/04/16 20:53, Stefan Weil wrote:
> Am 04.04.2016 um 15:22 schrieb Sergey Fedorov:
>> On 04/04/16 14:56, Stefan Weil wrote:
> [...]
>>> There is indeed a regression in the current code. Commit
>>> d38ea87ac54af64ef611de434d07c12dc0399216 added an include statement
>>> which includes assert.h before NDEBUG is defined. This is wrong and
>>> needs a fix. Could you please try tci.c starting like this?
>>>
>>> /* Defining NDEBUG disables assertions (which makes the code faster). */
>>> #if !defined(CONFIG_DEBUG_TCG) && !defined(NDEBUG)
>>> # define NDEBUG
>>> #endif
>>>
>>> #include "qemu/osdep.h"
>>>
>> Doing so really helps. So what are the plans of how to fix the problem?
>>
>> Thanks,
>> Sergey
>
> The correct fix needs a little bit more code because my first try (see
> above) did not get the definition of macro CONFIG_DEBUG_TCG.
>
> My patch was now sent to the list.

Thanks!