Fix __pthread_get_minstack()

This is the function that should take into account TLS block, and 1MB is
too high, since it will be used for sigaltstack() on SIGSEGV

v0: copy-paste glibc __pthread_get_minstack()
v2: return static 16K instead of 1MB

base/glibc-compatibility/glibc-compatibility.c

@@ -9,14 +9,36 @@ extern "C" {
 #endif
 
 #include <pthread.h>
+#include <unistd.h>
+#include <limits.h>
+#include <assert.h>
 
+/// glibc __pthread_get_minstack() will take TLS into account for the minimal
+/// stack size (since you cannot use stack less then TLS block size, otherwise
+/// some variables may be overwritten)
+///
+/// So glibc implementation is:
+///
+///     sysconf(_SC_PAGESIZE) + __static_tls_size + PTHREAD_STACK_MIN;
+///
+/// But this helper cannot do this since:
+/// - __pthread_get_minstack() is hidden in libc (note that rust tried to do
+///     this but revert it to retry loop, for compatibility, while we cannot
+///     use retry loop since this function is used for sigaltstack())
+/// - __static_tls_size is not exported in glibc
+/// - it is not used anywhere except for clickhouse itself (for sigaltstack(),
+///   to handle SIGSEGV only) and using PTHREAD_STACK_MIN (16k) is enough right
+///   now.
+///
+/// Also we cannot use getStackSize() (pthread_attr_getstack()) since it will
+/// return 8MB, and this is too huge for signal stack.
 size_t __pthread_get_minstack(const pthread_attr_t * attr)
 {
-    return 1048576;        /// This is a guess. Don't sure it is correct.
+    _Static_assert(PTHREAD_STACK_MIN == 16<<10, "Too small return value of __pthread_get_minstack()");
+    return PTHREAD_STACK_MIN;
 }
 
 #include <signal.h>
-#include <unistd.h>
 #include <string.h>
 #include <sys/syscall.h>