From a9182d06f8589c96c18c4a8f0ab9bcef678e6b12 Mon Sep 17 00:00:00 2001
From: Igor Todorovski <itodorov@ca.ibm.com>
Date: Thu, 14 May 2026 17:34:18 -0400
Subject: [PATCH] Add z/OS support with clang

Add the z/OS build-data entry, clang ABI flags, shared library linker handling, and s390x cycle counter support.

Move z/OS feature macros into the OS configuration and leave clang.txt with clang-specific flags only.

Disable the thread_local OS feature for z/OS and gate FFI exception storage on BOTAN_TARGET_OS_HAS_THREAD_LOCAL.

Tested with diff checks, z/OS configure generation, native configure, and native compilation of ffi.o and utils_os_utils.o.
---
 src/build-data/cc/clang.txt         |  4 +++-
 src/build-data/cc/gcc.txt           |  5 +++--
 src/build-data/os/zos.txt           | 29 +++++++++++++++++++++++++++++
 src/lib/ffi/ffi.cpp                 | 10 ++++++++--
 src/lib/utils/os_utils/os_utils.cpp |  8 ++++++++
 5 files changed, 51 insertions(+), 5 deletions(-)
 create mode 100644 src/build-data/os/zos.txt

diff --git a/src/build-data/cc/clang.txt b/src/build-data/cc/clang.txt
index d89da5deb7c..ebb39322097 100644
--- a/src/build-data/cc/clang.txt
+++ b/src/build-data/cc/clang.txt
@@ -52,6 +52,7 @@ macos         -> "{cxx} -dynamiclib -fPIC -install_name {libdir}/{soname_abi} -c
 
 # The default works for GNU ld and several other Unix linkers
 default       -> "{cxx} -shared -fPIC -Wl,-soname,{soname_abi}"
+zos           -> "{cxx} -shared -fPIC"
 
 mingw         -> "{cxx} -shared -Wl,--out-implib,{shared_lib_name}.a"
 </so_link_commands>
@@ -105,11 +106,12 @@ llvm    -> "-emit-llvm -fno-use-cxa-atexit"
 </cpu_flags>
 
 <mach_abi_linking>
-all!haiku,llvm -> "-pthread"
+all!haiku,llvm,zos -> "-pthread"
 
 x86_32  -> "-m32"
 x86_64  -> "-m64"
 ppc64   -> "-m64"
+zos     -> "-fzos-le-char-mode=ascii -mnocsect -fno-short-enums -m64 -mzos-target=zosv3r1"
 
 macos   -> "-stdlib=libc++"
 ios     -> "-stdlib=libc++"
diff --git a/src/build-data/cc/gcc.txt b/src/build-data/cc/gcc.txt
index 6a650589086..5c57c560aea 100644
--- a/src/build-data/cc/gcc.txt
+++ b/src/build-data/cc/gcc.txt
@@ -57,8 +57,9 @@ macos   -> "{cxx} -dynamiclib -fPIC -install_name {libdir}/{soname_abi}"
 hpux    -> "{cxx} -shared -fPIC -Wl,+h,{soname_abi}"
 solaris -> "{cxx} -shared -fPIC -Wl,-h,{soname_abi}"
 
-# AIX and OpenBSD don't use sonames at all
+# These platforms don't use sonames at all
 aix     -> "{cxx} -shared -fPIC"
+zos     -> "{cxx} -shared -fPIC"
 openbsd -> "{cxx} -shared -fPIC"
 
 mingw   -> "{cxx} -shared -Wl,--out-implib,{shared_lib_name}.a"
@@ -107,7 +108,7 @@ arm64:neon    -> ""
 
 # Flags set here are included at compile and link time
 <mach_abi_linking>
-all!haiku,qnx,none -> "-pthread"
+all!haiku,qnx,zos,none -> "-pthread"
 
 s390    -> "-m31"
 s390x   -> "-m64"
diff --git a/src/build-data/os/zos.txt b/src/build-data/os/zos.txt
new file mode 100644
index 00000000000..df1ed4b8687
--- /dev/null
+++ b/src/build-data/os/zos.txt
@@ -0,0 +1,29 @@
+soname_suffix "so"
+
+use_stack_protector no
+
+<feature_macros>
+_XOPEN_SOURCE=600
+_ALL_SOURCE
+_OPEN_SYS_FILE_EXT=1
+_AE_BIMODAL=1
+_ENHANCED_ASCII_EXT=0xFFFFFFFF
+</feature_macros>
+
+<target_features>
+posix1
+clock_gettime
+dev_random
+
+atomics
+sockets
+system_clock
+threads
+filesystem
+</target_features>
+
+<aliases>
+z/OS
+os/390
+os390
+</aliases>
diff --git a/src/lib/ffi/ffi.cpp b/src/lib/ffi/ffi.cpp
index 30f25f11a20..5fd508e9b2f 100644
--- a/src/lib/ffi/ffi.cpp
+++ b/src/lib/ffi/ffi.cpp
@@ -22,8 +22,14 @@ namespace Botan_FFI {
 
 namespace {
 
-// NOLINTNEXTLINE(*-avoid-non-const-global-variables)
-thread_local std::string g_last_exception_what;
+
+#if defined(BOTAN_TARGET_OS_HAS_THREAD_LOCAL)
+   // NOLINTNEXTLINE(*-avoid-non-const-global-variables)
+   thread_local std::string g_last_exception_what;
+#else
+   // NOLINTNEXTLINE(*-avoid-non-const-global-variables)
+   std::string g_last_exception_what;
+#endif
 
 int ffi_map_error_type(Botan::ErrorType err) {
    switch(err) {
diff --git a/src/lib/utils/os_utils/os_utils.cpp b/src/lib/utils/os_utils/os_utils.cpp
index 97922a0c7a9..7ae6e5b6c0b 100644
--- a/src/lib/utils/os_utils/os_utils.cpp
+++ b/src/lib/utils/os_utils/os_utils.cpp
@@ -71,6 +71,10 @@
    #include <kernel/OS.h>
 #endif
 
+#if defined(BOTAN_TARGET_OS_IS_ZOS)
+   #include <builtins.h>
+#endif
+
 namespace Botan {
 
 uint32_t OS::get_process_id() {
@@ -220,7 +224,11 @@ uint64_t OS::get_cpu_cycle_counter() {
    asm volatile("mov %0=ar.itc" : "=r"(rtc));
 
    #elif defined(BOTAN_TARGET_ARCH_IS_S390X)
+   #if defined(BOTAN_TARGET_OS_IS_ZOS)
+   __stckf(&rtc);
+   #else
    asm volatile("stck 0(%0)" : : "a"(&rtc) : "memory", "cc");
+   #endif
 
    #elif defined(BOTAN_TARGET_ARCH_IS_HPPA)
    asm volatile("mfctl 16,%0" : "=r"(rtc));  // 64-bit only?