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Posted to commits@nuttx.apache.org by GitBox <gi...@apache.org> on 2020/04/12 14:45:27 UTC
[GitHub] [incubator-nuttx] xiaoxiang781216 opened a new pull request #769:
misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
xiaoxiang781216 opened a new pull request #769: misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
URL: https://github.com/apache/incubator-nuttx/pull/769
Since the standard require ioctl has this prototype:
int ioctl(int fildes, int request, ... /* arg */);
https://pubs.opengroup.org/onlinepubs/009604599/functions/ioctl.html
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[GitHub] [incubator-nuttx] patacongo merged pull request #769: misc/Kconfig:
enable LIBC_IOCTL_VARIADIC by default
Posted by GitBox <gi...@apache.org>.
patacongo merged pull request #769: misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
URL: https://github.com/apache/incubator-nuttx/pull/769
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[GitHub] [incubator-nuttx] patacongo edited a comment on issue #769:
misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
Posted by GitBox <gi...@apache.org>.
patacongo edited a comment on issue #769: misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
URL: https://github.com/apache/incubator-nuttx/pull/769#issuecomment-612629522
This must be a new addition to the specs at OpenGroup.org. They did not specify ioctl at all in the past.
NOTE: That this is only a thin layer. It still only accepts one 'unsigned int' argument. But the ioctl layer just gets that using va_arg. See libs/libc/misc/lib_ioctl.c:
108 va_start(ap, req);
109 arg = va_arg(ap, unsigned long);
110 va_end(ap);
111
112 /* Then let fs_ioctl() to the real work */
113
114 return fs_ioctl(fd, req, arg);
It would take a lot of work to use this properly. And variadic functions cannot be used in syscalls so we would probably have to have a vioctl() as the primary OS interface.
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[GitHub] [incubator-nuttx] patacongo commented on issue #769: misc/Kconfig:
enable LIBC_IOCTL_VARIADIC by default
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #769: misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
URL: https://github.com/apache/incubator-nuttx/pull/769#issuecomment-612631905
> NOTE: That this is only a thin layer. It still only accepts one 'unsigned int' argument. But the ioctl layer just gets that using va_arg. See libs/libc/misc/lib_ioctl.c:
>
> ```
> 108 va_start(ap, req);
> 109 arg = va_arg(ap, unsigned long);
> 110 va_end(ap);
> 111
> 112 /* Then let fs_ioctl() to the real work */
> 113
> 114 return fs_ioctl(fd, req, arg);
> ```
That problem with that is that it is unsafe. Per comments in libs/libc/misc/lib_ioctl.c:
91 /* Get the unsigned long argument.
92 *
93 * REVISIT: This could be the cause of the crash down the road if the
94 * actual size of the argument is anything other than sizeof(unsigned long).
95 * Most small integers will be promoted to 'int'. ARM should pass the
96 * following test with all three types having sizeof(type) == 4 bytes.
97 * 'float' should also be tested. But 'long long' and 'double' are out of
98 * the question! Don't try to pass them.
99 *
100 * And what will happen if no third argument is passed? In most cases,
101 * this should just result in a garbage value for arg. But you may
102 * discover cases where something worse happens!
103 */
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[GitHub] [incubator-nuttx] patacongo commented on issue #769: misc/Kconfig:
enable LIBC_IOCTL_VARIADIC by default
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #769: misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
URL: https://github.com/apache/incubator-nuttx/pull/769#issuecomment-612629867
None of the ioctl commands listed on that page are defined or supported by NuttX either.
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[GitHub] [incubator-nuttx] patacongo commented on issue #769: misc/Kconfig:
enable LIBC_IOCTL_VARIADIC by default
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #769: misc/Kconfig: enable LIBC_IOCTL_VARIADIC by default
URL: https://github.com/apache/incubator-nuttx/pull/769#issuecomment-612629522
This must be a new addition to the specs at OpenGroup.org. They did not specify ioctl at all in the past.
NOTE: That this is only a thin layer. It still only accepts one 'unsigned int' argument. But the ioctl layer just gets that using va_arg. See libs/libc/misc/lib_ioctl.c:
108 va_start(ap, req);
109 arg = va_arg(ap, unsigned long);
110 va_end(ap);
111
112 /* Then let fs_ioctl() to the real work */
113
114 return fs_ioctl(fd, req, arg);
It would take a lot of work to use this properly. And variadic functions cannot be used in syscalls so we would probably have to have a vioctl().
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