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[PATCH] tools/libxl: remove usage of VLA arrays

Roger Pau Monne posted 1 patch 3 weeks, 3 days ago
Patches applied successfully (tree, apply log)
git fetch https://gitlab.com/xen-project/patchew/xen tags/patchew/20241028114831.27487-1-roger.pau@citrix.com
tools/libs/light/libxl_utils.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
[PATCH] tools/libxl: remove usage of VLA arrays
Posted by Roger Pau Monne 3 weeks, 3 days ago 
Clang 19 complains with the following error when building libxl:

libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
   48 |     char path[strlen("/local/domain") + 12];
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
string length to be known at build time.  Note ARRAY_SIZE() accounts for the
NUL terminator while strlen() didn't, hence subtract 1 from the total size
calculation.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 tools/libs/light/libxl_utils.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
index 10398a6c8611..b3f5e751cc3f 100644
--- a/tools/libs/light/libxl_utils.c
+++ b/tools/libs/light/libxl_utils.c
@@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
 char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
 {
     unsigned int len;
-    char path[strlen("/local/domain") + 12];
+    char path[ARRAY_SIZE("/local/domain") + 11];
     char *s;
 
     snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
@@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
 char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
 {
     unsigned int len;
-    char path[strlen("/local/pool") + 12];
+    char path[ARRAY_SIZE("/local/pool") + 11];
     char *s;
 
     snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
-- 
2.46.0
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Andrew Cooper 3 weeks, 2 days ago 
On 28/10/2024 11:48 am, Roger Pau Monne wrote:
> Clang 19 complains with the following error when building libxl:
>
> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
>    48 |     char path[strlen("/local/domain") + 12];
>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
> NUL terminator while strlen() didn't, hence subtract 1 from the total size
> calculation.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
>  tools/libs/light/libxl_utils.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
> index 10398a6c8611..b3f5e751cc3f 100644
> --- a/tools/libs/light/libxl_utils.c
> +++ b/tools/libs/light/libxl_utils.c
> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
>  {
>      unsigned int len;
> -    char path[strlen("/local/domain") + 12];
> +    char path[ARRAY_SIZE("/local/domain") + 11];
>      char *s;
>  
>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
>  {
>      unsigned int len;
> -    char path[strlen("/local/pool") + 12];
> +    char path[ARRAY_SIZE("/local/pool") + 11];
>      char *s;
>  
>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

Although I have a minor preference for sizeof() as suggested by Frediano.

Can fix on commit, if you're happy?

~Andrew
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Anthony PERARD 2 weeks, 1 day ago 
On Mon, Oct 28, 2024 at 12:03:59PM +0000, Andrew Cooper wrote:
> On 28/10/2024 11:48 am, Roger Pau Monne wrote:
> > Clang 19 complains with the following error when building libxl:
> >
> > libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
> >    48 |     char path[strlen("/local/domain") + 12];
> >       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
> > string length to be known at build time.  Note ARRAY_SIZE() accounts for the
> > NUL terminator while strlen() didn't, hence subtract 1 from the total size
> > calculation.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > ---
> >  tools/libs/light/libxl_utils.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
> > index 10398a6c8611..b3f5e751cc3f 100644
> > --- a/tools/libs/light/libxl_utils.c
> > +++ b/tools/libs/light/libxl_utils.c
> > @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
> >  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
> >  {
> >      unsigned int len;
> > -    char path[strlen("/local/domain") + 12];
> > +    char path[ARRAY_SIZE("/local/domain") + 11];
> >      char *s;
> >  
> >      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
> > @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
> >  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
> >  {
> >      unsigned int len;
> > -    char path[strlen("/local/pool") + 12];
> > +    char path[ARRAY_SIZE("/local/pool") + 11];
> >      char *s;
> >  
> >      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
> 
> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> Although I have a minor preference for sizeof() as suggested by Frediano.

I have a preference for sizeof() too, we even used it this way (more or
less) in libxl before, for `eom` here:
    https://elixir.bootlin.com/xen/v4.19.0/source/tools/libs/light/libxl_qmp.c#L1608

I was a bit supprised by the use of ARRAY_SIZE on a string literal but
it's just an array of char :-).

For the patch, with sizeof() or ARRAY_SIZE():
Acked-by: Anthony PERARD <anthony.perard@vates.tech>

Thanks,

-- 

Anthony Perard | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Andrew Cooper 2 weeks, 1 day ago 
On 05/11/2024 3:05 pm, Anthony PERARD wrote:
> On Mon, Oct 28, 2024 at 12:03:59PM +0000, Andrew Cooper wrote:
>> On 28/10/2024 11:48 am, Roger Pau Monne wrote:
>>> Clang 19 complains with the following error when building libxl:
>>>
>>> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
>>>    48 |     char path[strlen("/local/domain") + 12];
>>>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>
>>> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
>>> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
>>> NUL terminator while strlen() didn't, hence subtract 1 from the total size
>>> calculation.
>>>
>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>>> ---
>>>  tools/libs/light/libxl_utils.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
>>> index 10398a6c8611..b3f5e751cc3f 100644
>>> --- a/tools/libs/light/libxl_utils.c
>>> +++ b/tools/libs/light/libxl_utils.c
>>> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
>>>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
>>>  {
>>>      unsigned int len;
>>> -    char path[strlen("/local/domain") + 12];
>>> +    char path[ARRAY_SIZE("/local/domain") + 11];
>>>      char *s;
>>>  
>>>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
>>> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
>>>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
>>>  {
>>>      unsigned int len;
>>> -    char path[strlen("/local/pool") + 12];
>>> +    char path[ARRAY_SIZE("/local/pool") + 11];
>>>      char *s;
>>>  
>>>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
>> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>
>> Although I have a minor preference for sizeof() as suggested by Frediano.
> I have a preference for sizeof() too, we even used it this way (more or
> less) in libxl before, for `eom` here:
>     https://elixir.bootlin.com/xen/v4.19.0/source/tools/libs/light/libxl_qmp.c#L1608
>
> I was a bit supprised by the use of ARRAY_SIZE on a string literal but
> it's just an array of char :-).
>
> For the patch, with sizeof() or ARRAY_SIZE():
> Acked-by: Anthony PERARD <anthony.perard@vates.tech>

That's 3 for sizeof(), one ambivalent, and one for ARRAY_SIZE(), with
the maintainer (who gets the majority say) already in the largest group
already.

I've adjusted and committed.

~Andrew
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Jan Beulich 3 weeks, 2 days ago 
On 28.10.2024 13:03, Andrew Cooper wrote:
> On 28/10/2024 11:48 am, Roger Pau Monne wrote:
>> Clang 19 complains with the following error when building libxl:
>>
>> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
>>    48 |     char path[strlen("/local/domain") + 12];
>>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
>> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
>> NUL terminator while strlen() didn't, hence subtract 1 from the total size
>> calculation.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>> ---
>>  tools/libs/light/libxl_utils.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
>> index 10398a6c8611..b3f5e751cc3f 100644
>> --- a/tools/libs/light/libxl_utils.c
>> +++ b/tools/libs/light/libxl_utils.c
>> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
>>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
>>  {
>>      unsigned int len;
>> -    char path[strlen("/local/domain") + 12];
>> +    char path[ARRAY_SIZE("/local/domain") + 11];
>>      char *s;
>>  
>>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
>> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
>>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
>>  {
>>      unsigned int len;
>> -    char path[strlen("/local/pool") + 12];
>> +    char path[ARRAY_SIZE("/local/pool") + 11];
>>      char *s;
>>  
>>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
> 
> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> Although I have a minor preference for sizeof() as suggested by Frediano.
> 
> Can fix on commit, if you're happy?

Please can we stick to ARRAY_SIZE() when it comes to strings? It's the
same as sizeof() when the base type is char, but the difference becomes
relevant if the base type was e.g. wchar_t.

Jan
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Frediano Ziglio 3 weeks, 2 days ago 
On Mon, Oct 28, 2024 at 12:48 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 28.10.2024 13:03, Andrew Cooper wrote:
> > On 28/10/2024 11:48 am, Roger Pau Monne wrote:
> >> Clang 19 complains with the following error when building libxl:
> >>
> >> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
> >>    48 |     char path[strlen("/local/domain") + 12];
> >>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>
> >> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
> >> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
> >> NUL terminator while strlen() didn't, hence subtract 1 from the total size
> >> calculation.
> >>
> >> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> >> ---
> >>  tools/libs/light/libxl_utils.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
> >> index 10398a6c8611..b3f5e751cc3f 100644
> >> --- a/tools/libs/light/libxl_utils.c
> >> +++ b/tools/libs/light/libxl_utils.c
> >> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
> >>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
> >>  {
> >>      unsigned int len;
> >> -    char path[strlen("/local/domain") + 12];
> >> +    char path[ARRAY_SIZE("/local/domain") + 11];
> >>      char *s;
> >>
> >>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
> >> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
> >>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
> >>  {
> >>      unsigned int len;
> >> -    char path[strlen("/local/pool") + 12];
> >> +    char path[ARRAY_SIZE("/local/pool") + 11];
> >>      char *s;
> >>
> >>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
> >
> > Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> >
> > Although I have a minor preference for sizeof() as suggested by Frediano.
> >
> > Can fix on commit, if you're happy?
>
> Please can we stick to ARRAY_SIZE() when it comes to strings? It's the
> same as sizeof() when the base type is char, but the difference becomes
> relevant if the base type was e.g. wchar_t.
>
> Jan
>

But "literal" is not a wide string, and the type is "char" which is
not wide too.

BTW, both me and Andrew are not strong about.

Frediano
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Roger Pau Monné 3 weeks, 2 days ago 
On Mon, Oct 28, 2024 at 12:57:30PM +0000, Frediano Ziglio wrote:
> On Mon, Oct 28, 2024 at 12:48 PM Jan Beulich <jbeulich@suse.com> wrote:
> >
> > On 28.10.2024 13:03, Andrew Cooper wrote:
> > > On 28/10/2024 11:48 am, Roger Pau Monne wrote:
> > >> Clang 19 complains with the following error when building libxl:
> > >>
> > >> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
> > >>    48 |     char path[strlen("/local/domain") + 12];
> > >>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >>
> > >> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
> > >> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
> > >> NUL terminator while strlen() didn't, hence subtract 1 from the total size
> > >> calculation.
> > >>
> > >> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > >> ---
> > >>  tools/libs/light/libxl_utils.c | 4 ++--
> > >>  1 file changed, 2 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
> > >> index 10398a6c8611..b3f5e751cc3f 100644
> > >> --- a/tools/libs/light/libxl_utils.c
> > >> +++ b/tools/libs/light/libxl_utils.c
> > >> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
> > >>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
> > >>  {
> > >>      unsigned int len;
> > >> -    char path[strlen("/local/domain") + 12];
> > >> +    char path[ARRAY_SIZE("/local/domain") + 11];
> > >>      char *s;
> > >>
> > >>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
> > >> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
> > >>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
> > >>  {
> > >>      unsigned int len;
> > >> -    char path[strlen("/local/pool") + 12];
> > >> +    char path[ARRAY_SIZE("/local/pool") + 11];
> > >>      char *s;
> > >>
> > >>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
> > >
> > > Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> > >
> > > Although I have a minor preference for sizeof() as suggested by Frediano.
> > >
> > > Can fix on commit, if you're happy?
> >
> > Please can we stick to ARRAY_SIZE() when it comes to strings? It's the
> > same as sizeof() when the base type is char, but the difference becomes
> > relevant if the base type was e.g. wchar_t.
> >
> > Jan
> >
> 
> But "literal" is not a wide string, and the type is "char" which is
> not wide too.
> 
> BTW, both me and Andrew are not strong about.

No strong opinion either, I've assumed it was clearer to not make
implicit assumptions about the size of the string literal array
elements.  I would rather like to get this committed, and Jan seems to
prefer to use ARRAY_SIZE(), so I suggest we get the patch committed
as-is.

Thanks, Roger.
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Jan Beulich 3 weeks, 2 days ago 
On 28.10.2024 18:26, Roger Pau Monné wrote:
> On Mon, Oct 28, 2024 at 12:57:30PM +0000, Frediano Ziglio wrote:
>> On Mon, Oct 28, 2024 at 12:48 PM Jan Beulich <jbeulich@suse.com> wrote:
>>>
>>> On 28.10.2024 13:03, Andrew Cooper wrote:
>>>> On 28/10/2024 11:48 am, Roger Pau Monne wrote:
>>>>> Clang 19 complains with the following error when building libxl:
>>>>>
>>>>> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
>>>>>    48 |     char path[strlen("/local/domain") + 12];
>>>>>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>
>>>>> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
>>>>> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
>>>>> NUL terminator while strlen() didn't, hence subtract 1 from the total size
>>>>> calculation.
>>>>>
>>>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>>>>> ---
>>>>>  tools/libs/light/libxl_utils.c | 4 ++--
>>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
>>>>> index 10398a6c8611..b3f5e751cc3f 100644
>>>>> --- a/tools/libs/light/libxl_utils.c
>>>>> +++ b/tools/libs/light/libxl_utils.c
>>>>> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
>>>>>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
>>>>>  {
>>>>>      unsigned int len;
>>>>> -    char path[strlen("/local/domain") + 12];
>>>>> +    char path[ARRAY_SIZE("/local/domain") + 11];
>>>>>      char *s;
>>>>>
>>>>>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
>>>>> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
>>>>>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
>>>>>  {
>>>>>      unsigned int len;
>>>>> -    char path[strlen("/local/pool") + 12];
>>>>> +    char path[ARRAY_SIZE("/local/pool") + 11];
>>>>>      char *s;
>>>>>
>>>>>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
>>>>
>>>> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>>>
>>>> Although I have a minor preference for sizeof() as suggested by Frediano.
>>>>
>>>> Can fix on commit, if you're happy?
>>>
>>> Please can we stick to ARRAY_SIZE() when it comes to strings? It's the
>>> same as sizeof() when the base type is char, but the difference becomes
>>> relevant if the base type was e.g. wchar_t.
>>>
>>> Jan
>>>
>>
>> But "literal" is not a wide string, and the type is "char" which is
>> not wide too.
>>
>> BTW, both me and Andrew are not strong about.
> 
> No strong opinion either, I've assumed it was clearer to not make
> implicit assumptions about the size of the string literal array
> elements.  I would rather like to get this committed, and Jan seems to
> prefer to use ARRAY_SIZE(), so I suggest we get the patch committed
> as-is.

Well, ultimately it's Anthony's call, for still being the sole maintainer.

Jan
Re: [PATCH] tools/libxl: remove usage of VLA arrays
Posted by Frediano Ziglio 3 weeks, 3 days ago 
On Mon, Oct 28, 2024 at 11:48 AM Roger Pau Monne <roger.pau@citrix.com> wrote:
>
> Clang 19 complains with the following error when building libxl:
>
> libxl_utils.c:48:15: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
>    48 |     char path[strlen("/local/domain") + 12];
>       |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Replace the usage of strlen() with ARRAY_SIZE(), which allows the literal
> string length to be known at build time.  Note ARRAY_SIZE() accounts for the
> NUL terminator while strlen() didn't, hence subtract 1 from the total size
> calculation.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
>  tools/libs/light/libxl_utils.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
> index 10398a6c8611..b3f5e751cc3f 100644
> --- a/tools/libs/light/libxl_utils.c
> +++ b/tools/libs/light/libxl_utils.c
> @@ -45,7 +45,7 @@ unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, unsigned
>  char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
>  {
>      unsigned int len;
> -    char path[strlen("/local/domain") + 12];
> +    char path[ARRAY_SIZE("/local/domain") + 11];
>      char *s;
>
>      snprintf(path, sizeof(path), "/local/domain/%d/name", domid);
> @@ -141,7 +141,7 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, const char *p,
>  char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
>  {
>      unsigned int len;
> -    char path[strlen("/local/pool") + 12];
> +    char path[ARRAY_SIZE("/local/pool") + 11];
>      char *s;
>
>      snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);

Minor: why not sizeof instead of ARRAY_SIZE ?

Not a regression, but looking at final strings and size added, it
looks like the numbers should be more uint16_t than uint32_t.
Maybe we want something like

    char path[sizeof("/local/pool//name") + 12];

BTW,

Reviewed-by: Frediano Ziglio <frediano.ziglio@cloud.com>

Frediano

Patchew 2.1-devel-b67e4c2

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