gh-142379: configure.ac: detect unusable termio operations #142380
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Some termio operations are not actually usable on some architectures. For example, the TCGETA, TCSETA, TCSETAF and TCSETAW are defined with a reference to "struct termio" on alpha, hppa and sparc64, but "struct termio" is no longer defined since glibc 2.42, causing a build failure. Instead of using those operations as soon as they are defined, this commit checks more carefully that they are actually usable. This is done using a new m4 macro PY_CHECK_IOCTL. Signed-off-by: Thomas Petazzoni <[email protected]>
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| {"TCFLSH", TCFLSH}, | ||
| #endif | ||
| #ifdef TCGETA | ||
| #if defined(HAVE_TCGETA) |
| dnl PY_CHECK_IOCTL(IOCTL_SYMBOL) | ||
| AC_DEFUN([PY_CHECK_IOCTL], | ||
| [ | ||
| AC_MSG_CHECKING([for $1]) | ||
| AC_COMPILE_IFELSE( | ||
| [AC_LANG_PROGRAM( | ||
| [[#include <sys/ioctl.h>]], | ||
| [[ | ||
| /* Test whether $1 is declared */ | ||
| long val = $1; | ||
| return 0; | ||
| ]] | ||
| )], | ||
| [AC_MSG_RESULT([yes]) | ||
| AC_DEFINE([HAVE_$1], [1], | ||
| [Define this if $1 termio operation is usable])], | ||
| [AC_MSG_RESULT([no])] | ||
| ) | ||
| ]) |
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Can you make this a generic function instead? it's useful for checking the presence of a macro. Make the includes and the expected macro type parameters of that function, as well as the name of your HAVE_ macro as you did. This could be useful elsewhere.
Ina ddition, there is no need for the return 0; as it's implicit. Also remove `/* Test whether $1 is declared */ because it's trivial what it does.
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Thanks for the feedback @picnixz. Actually such a generic macro already "exists" to some degree, it's AC_CHECK_DECL. However, we can't use it in our specific case because what AC_CHECK_DECL does is:
#ifndef YOUR_DECLARATION
(void) YOUR_DECLARATION;
#endif
The idea being: the #ifndef test if it is a macro => if it is, then fine, we're good. If it's not a macro, it checks if it's a valid r-value.
In our case, TCGETA is a macro, BUT we need to check that it is actually usable, not just "defined". And that's why AC_CHECK_DECL doesn't do the trick.
If you still think a generic macro would be good, what name should it have? Indeed, PY_CHECK_DECL would be very confusing if it has this subtle difference with AC_CHECK_DECL. Or maybe PY_CHECK_USABLE_DECL ?
And of course, our macro isn't as generic as AC_CHECK_DECL, because if the declaration exists but has no value (like #define FOO), then our test will fail.
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My idea was actually different. What I wanted to test is:
TYPE holder = $1;
where you specify TYPE (in your case it's long). And for the name, it would be PY_CHECK_CONSTANT. I wanted you to actually remove the comment but not the test itself.
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Makes a lot of sense, will do!
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Some termio operations are not actually usable on some architectures. For example, the TCGETA, TCSETA, TCSETAF and TCSETAW are defined with a reference to "struct termio" on alpha, hppa and sparc64, but "struct termio" is no longer defined since glibc 2.42, causing a build failure.
Instead of using those operations as soon as they are defined, this commit checks more carefully that they are actually usable. This is done using a new m4 macro PY_CHECK_IOCTL.