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gh-159320: use pthread_getattr_np for stack limit checks even on musl - #159376
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reporting the stack limit of the main thread incorrectly. On platforms where pthread_getattr_np underreports the main thread's stack size, use RLIMIT_STACK for the main thread instead.
Yhg1s
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AA-Turner,
Eclips4,
corona10,
emmatyping,
erlend-aasland,
itamaro,
markshannon and
tomasr8
as code owners
October 13, 2026 21:31
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This is a more general fix than #159321, and incidentally also lets us have proper stack overflow protections on musl. |
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For the record, I think this should not be backported. |
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encukou
reviewed
Oct 16, 2026
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Python/ceval.c
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…doesn't depend on explicitly setting the stack size. It's correct for new threads regardless of that call.
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Can you please make the new "HAVE" macro private? Replace the macro in configure.ac: - [AC_DEFINE([HAVE_UNRELIABLE_PTHREAD_GETATTR_NP], [1],
+ [AC_DEFINE([_Py_HAVE_UNRELIABLE_PTHREAD_GETATTR_NP], [1],Something like that: Detailsdiff --git a/Python/ceval.c b/Python/ceval.c
index 3ed070a5846..e0623293670 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -65,7 +65,7 @@ _Py_ReachedRecursionLimitWithMargin(PyThreadState *tstate, int margin_count)
# define Py_C_STACK_SIZE 4000000
#endif
-#ifdef HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
+#ifdef _Py_HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
#ifdef HAVE_SYS_RESOURCE_H
# include <sys/resource.h>
#endif
@@ -165,7 +165,7 @@ hardware_stack_limits(uintptr_t *base, uintptr_t *top, uintptr_t sp)
err |= pthread_attr_destroy(&attr);
}
if (err == 0) {
-# ifdef HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
+# ifdef _Py_HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
/* pthread_getattr_np on the main thread of a musl process reports a
* stack size based on the current stack rather than RLIMIT_STACK.
* New threads are reported correctly even on musl, so this fallback
diff --git a/Tools/build/check_capi_macros_ignored.txt b/Tools/build/check_capi_macros_ignored.txt
index cfa37c2b137..238c29b7039 100644
--- a/Tools/build/check_capi_macros_ignored.txt
+++ b/Tools/build/check_capi_macros_ignored.txt
@@ -627,7 +627,6 @@ HAVE_UNAME
HAVE_UNISTD_H
HAVE_UNLINKAT
HAVE_UNLOCKPT
-HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
HAVE_UNSHARE
HAVE_USABLE_WCHAR_T
HAVE_UTIL_H
diff --git a/configure b/configure
index 221907add48..744ee2beef4 100755
--- a/configure
+++ b/configure
@@ -21875,7 +21875,7 @@ printf "%s\n" "$ac_cv_unreliable_pthread_getattr_np" >&6; }
if test "x$ac_cv_unreliable_pthread_getattr_np" = xyes
then :
-printf "%s\n" "#define HAVE_UNRELIABLE_PTHREAD_GETATTR_NP 1" >>confdefs.h
+printf "%s\n" "#define _Py_HAVE_UNRELIABLE_PTHREAD_GETATTR_NP 1" >>confdefs.h
fi
fi
diff --git a/configure.ac b/configure.ac
index e523314b492..42844ab64ca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5620,7 +5620,7 @@ int main(void) {
[ac_cv_unreliable_pthread_getattr_np=yes],
[ac_cv_unreliable_pthread_getattr_np=no])])
AS_VAR_IF([ac_cv_unreliable_pthread_getattr_np], [yes],
- [AC_DEFINE([HAVE_UNRELIABLE_PTHREAD_GETATTR_NP], [1],
+ [AC_DEFINE([_Py_HAVE_UNRELIABLE_PTHREAD_GETATTR_NP], [1],
[Define if pthread_getattr_np under-reports the main thread's stack size (musl behaviour).])])])
# os.statx uses Linux's statx function. AIX also has a function named statx,
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 4193d536f3b..1fdeb7d9f2f 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -1706,10 +1706,6 @@
/* Define to 1 if you have the 'unlockpt' function. */
#undef HAVE_UNLOCKPT
-/* Define if pthread_getattr_np under-reports the main thread's stack size
- (musl behaviour). */
-#undef HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
-
/* Define to 1 if you have the 'unshare' function. */
#undef HAVE_UNSHARE
@@ -2227,6 +2223,10 @@
/* Define if you have the 'tanpi' function. */
#undef _Py_HAVE_TANPI
+/* Define if pthread_getattr_np under-reports the main thread's stack size
+ (musl behaviour). */
+#undef _Py_HAVE_UNRELIABLE_PTHREAD_GETATTR_NP
+
/* Thread stack size set by the linker (in bytes). */
#undef _Py_LINKER_THREAD_STACK_SIZE
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Adjust the use of pthread_getattr_np for stack size limit detection to avoid the problem on musl of it reporting the stack limit of the main thread incorrectly. On platforms where pthread_getattr_np underreports the main thread's stack size, use RLIMIT_STACK for the main thread instead. (Cross-compiles targeting musl will have to pass ac_cv_unreliable_pthread_getattr_np=yes to configure.)