[igt-dev] [PATCH i-g-t v2 2/2] build: provide stub implementation for memfd_create

[Antonio Argenziano]

On 25/07/18 12:57, De Marchi, Lucas wrote:
> On Wed, 2018-07-25 at 09:46 -0700, Antonio Argenziano wrote:
>>
>> On 24/07/18 15:20, Lucas De Marchi wrote:
>>> When libc misses memfd_create(), provide a stub implementation to go
>>> through the syscall() route. Syscall numbers are provided for platforms
>>> currently supported by i-g-t only.
>>>
>>> v2: add support to autotools
>>>
>>> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
>>> ---
>>>    configure.ac                  |  3 +++
>>>    lib/stubs/syscalls/sys/mman.h | 37 +++++++++++++++++++++++++++++++++++
>>>    meson.build                   |  3 +++
>>
>> I thought you were going to remove "#include <linux/memfd.h>" from
>> gem_userptr_blits and include the stub instead.
> 
> I decided not to. To summarize:
> 
> In order to get the memfd_create() function definition one needs to include
> sys/mman.h. The man page is wrong and I sent a patch.
> 
> linux/memfd.h is the kernel header (i.e. not from libc). It's useful to have
> it if we are using or going to use new flags not present in the libc headers.
> Or harmless. This is their content for me:
> 
> kernel header (linux/memfd.h):
> /* flags for memfd_create(2) (unsigned int) */
> #define MFD_CLOEXEC             0x0001U
> #define MFD_ALLOW_SEALING       0x0002U
> #define MFD_HUGETLB             0x0004U
> 
> libc header (bits/mman-shared.h which is down the include chain for
> sys/mman.h):
> 
> #ifdef __USE_GNU
> /* Flags for memfd_create.  */
> # ifndef MFD_CLOEXEC
> #  define MFD_CLOEXEC 1U
> #  define MFD_ALLOW_SEALING 2U
> #  define MFD_HUGETLB 4U
> # endif
> ...
> 
> We could also check if linux/memfd.h is available or just remove the include
> since we are not using any flag not available on libc, but IMO it's not
> necessary or at least not for this patch.

Fair enough, time for me to modernize a little anyway :).

For both patches:
Acked-by: Antonio Argenziano <antonio.argenziano at intel.com>

> 
> 
> Lucas De Marchi
> 
>>
>> Antonio.
>>
>>>    3 files changed, 43 insertions(+)
>>>    create mode 100644 lib/stubs/syscalls/sys/mman.h
>>>
>>> diff --git a/configure.ac b/configure.ac
>>> index 0a5b0425..416a3240 100644
>>> --- a/configure.ac
>>> +++ b/configure.ac
>>> @@ -81,6 +81,9 @@ AC_CHECK_FUNCS(timer_create, [], [
>>>    ])
>>>    AC_SUBST(TIMER_LIBS)
>>>    
>>> +dnl Check for memfd_create
>>> +AC_CHECK_FUNCS(memfd_create)
>>> +
>>>    dnl Check for CPUID
>>>    cpuid="yes"
>>>    AC_TRY_LINK([
>>> diff --git a/lib/stubs/syscalls/sys/mman.h b/lib/stubs/syscalls/sys/mman.h
>>> new file mode 100644
>>> index 00000000..2ac2da6a
>>> --- /dev/null
>>> +++ b/lib/stubs/syscalls/sys/mman.h
>>> @@ -0,0 +1,37 @@
>>> +/* SPDX-License-Identifier: MIT */
>>> +
>>> +#pragma once
>>> +
>>> +#include_next <sys/mman.h>
>>> +
>>> +#if !defined(HAVE_MEMFD_CREATE) || !HAVE_MEMFD_CREATE
>>> +#include <errno.h>
>>> +#include <sys/syscall.h>
>>> +#include <sys/types.h>
>>> +#include <unistd.h>
>>> +
>>> +#ifndef __NR_memfd_create
>>> +#if defined __x86_64__
>>> +#define __NR_memfd_create 319
>>> +#elif defined __i386__
>>> +#define __NR_memfd_create 356
>>> +#elif defined __arm__
>>> +#define __NR_memfd_create 385
>>> +#else
>>> +#warning "__NR_memfd_create unknown for your architecture"
>>> +#endif
>>> +#endif
>>> +
>>> +static inline int missing_memfd_create(const char *name, unsigned int
>>> flags)
>>> +{
>>> +#ifdef __NR_memfd_create
>>> +	return syscall(__NR_memfd_create, name, flags);
>>> +#else
>>> +	errno = ENOSYS;
>>> +	return -1;
>>> +#endif
>>> +}
>>> +
>>> +#define memfd_create missing_memfd_create
>>> +
>>> +#endif
>>> diff --git a/meson.build b/meson.build
>>> index 22118828..63ac6292 100644
>>> --- a/meson.build
>>> +++ b/meson.build
>>> @@ -196,6 +196,9 @@ if cc.has_member('struct sysinfo', 'totalram',
>>>    	config.set('HAVE_STRUCT_SYSINFO_TOTALRAM', 1)
>>>    endif
>>>    
>>> +have = cc.has_function('memfd_create', prefix : '''#include
>>> <sys/mman.h>''', args : '-D_GNU_SOURCE')
>>> +config.set10('HAVE_MEMFD_CREATE', have)
>>> +
>>>    add_project_arguments('-D_GNU_SOURCE', language : 'c')
>>>    add_project_arguments('-include', 'config.h', language : 'c')
>>>    
>>>