cmake: Add check_arm32_assembly function

Author: hebasto

.cirrus.yml

@@ -176,7 +176,7 @@ task:
     CTIMETESTS: no
   matrix:
     - env: {}
-    - env: {EXPERIMENTAL: yes, ASM: arm}
+    - env: {EXPERIMENTAL: yes, ASM: arm32}
   << : *MERGE_BASE
   test_script:
     - ./ci/cirrus.sh

CMakeLists.txt

@@ -102,12 +102,18 @@ if(SECP256K1_TEST_OVERRIDE_WIDE_MULTIPLY)
 endif()
 mark_as_advanced(FORCE SECP256K1_TEST_OVERRIDE_WIDE_MULTIPLY)
 
-set(SECP256K1_ASM "AUTO" CACHE STRING "Assembly optimizations to use: \"AUTO\", \"OFF\", \"x86_64\" or \"arm\" (experimental). [default=AUTO]")
-set_property(CACHE SECP256K1_ASM PROPERTY STRINGS "AUTO" "OFF" "x86_64" "arm")
+set(SECP256K1_ASM "AUTO" CACHE STRING "Assembly optimizations to use: \"AUTO\", \"OFF\", \"x86_64\" or \"arm32\" (experimental). [default=AUTO]")
+set_property(CACHE SECP256K1_ASM PROPERTY STRINGS "AUTO" "OFF" "x86_64" "arm32")
 check_string_option_value(SECP256K1_ASM)
-if(SECP256K1_ASM STREQUAL "arm")
+if(SECP256K1_ASM STREQUAL "arm32")
   enable_language(ASM)
-  add_compile_definitions(USE_EXTERNAL_ASM=1)
+  include(CheckArm32Assembly)
+  check_arm32_assembly()
+  if(HAVE_ARM32_ASM)
+    add_compile_definitions(USE_EXTERNAL_ASM=1)
+  else()
+    message(FATAL_ERROR "ARM32 assembly optimization requested but not available.")
+  endif()
 elseif(SECP256K1_ASM)
   include(Check64bitAssembly)
   check_64bit_assembly()
@@ -123,8 +129,8 @@ endif()
 
 option(SECP256K1_EXPERIMENTAL "Allow experimental configuration options." OFF)
 if(NOT SECP256K1_EXPERIMENTAL)
-  if(SECP256K1_ASM STREQUAL "arm")
-    message(FATAL_ERROR "ARM assembly optimization is experimental. Use -DSECP256K1_EXPERIMENTAL=ON to allow.")
+  if(SECP256K1_ASM STREQUAL "arm32")
+    message(FATAL_ERROR "ARM32 assembly optimization is experimental. Use -DSECP256K1_EXPERIMENTAL=ON to allow.")
   endif()
 endif()
 

cmake/CheckArm32Assembly.cmake

@@ -0,0 +1,6 @@
+function(check_arm32_assembly)
+  try_compile(HAVE_ARM32_ASM
+    ${CMAKE_BINARY_DIR}/check_arm32_assembly
+    SOURCES ${CMAKE_SOURCE_DIR}/cmake/source_arm32.s
+  )
+endfunction()

cmake/source_arm32.s

@@ -0,0 +1,9 @@
+.syntax unified
+.eabi_attribute 24, 1
+.eabi_attribute 25, 1
+.text
+.global main
+main:
+	ldr	r0, =0x002A
+	mov	r7, #1
+	swi	0   

configure.ac

@@ -197,8 +197,8 @@ AC_ARG_ENABLE(external_default_callbacks,
 #  *  and auto (the default).
 AC_ARG_WITH([test-override-wide-multiply], [] ,[set_widemul=$withval], [set_widemul=auto])
 
-AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm|no|auto],
-[assembly optimizations to use (experimental: arm) [default=auto]])],[req_asm=$withval], [req_asm=auto])
+AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm32|no|auto],
+[assembly optimizations to use (experimental: arm32) [default=auto]])],[req_asm=$withval], [req_asm=auto])
 
 AC_ARG_WITH([ecmult-window], [AS_HELP_STRING([--with-ecmult-window=SIZE|auto],
 [window size for ecmult precomputation for verification, specified as integer in range [2..24].]
@@ -279,7 +279,7 @@ else
       AC_MSG_ERROR([x86_64 assembly optimization requested but not available])
     fi
     ;;
-  arm)
+  arm32)
     ;;
   no)
     ;;
@@ -296,7 +296,7 @@ case $set_asm in
 x86_64)
   SECP_CONFIG_DEFINES="$SECP_CONFIG_DEFINES -DUSE_ASM_X86_64=1"
   ;;
-arm)
+arm32)
   enable_external_asm=yes
   ;;
 no)
@@ -413,8 +413,8 @@ if test x"$enable_experimental" = x"yes"; then
   AC_MSG_NOTICE([Experimental features do not have stable APIs or properties, and may not be safe for production use.])
   AC_MSG_NOTICE([******])
 else
-  if test x"$set_asm" = x"arm"; then
-    AC_MSG_ERROR([ARM assembly optimization is experimental. Use --enable-experimental to allow.])
+  if test x"$set_asm" = x"arm32"; then
+    AC_MSG_ERROR([ARM32 assembly optimization is experimental. Use --enable-experimental to allow.])
   fi
 fi
 
@@ -436,7 +436,7 @@ AM_CONDITIONAL([ENABLE_MODULE_RECOVERY], [test x"$enable_module_recovery" = x"ye
 AM_CONDITIONAL([ENABLE_MODULE_EXTRAKEYS], [test x"$enable_module_extrakeys" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_SCHNORRSIG], [test x"$enable_module_schnorrsig" = x"yes"])
 AM_CONDITIONAL([USE_EXTERNAL_ASM], [test x"$enable_external_asm" = x"yes"])
-AM_CONDITIONAL([USE_ASM_ARM], [test x"$set_asm" = x"arm"])
+AM_CONDITIONAL([USE_ASM_ARM], [test x"$set_asm" = x"arm32"])
 AM_CONDITIONAL([BUILD_WINDOWS], [test "$build_windows" = "yes"])
 AC_SUBST(LIB_VERSION_CURRENT, _LIB_VERSION_CURRENT)
 AC_SUBST(LIB_VERSION_REVISION, _LIB_VERSION_REVISION)

src/CMakeLists.txt

@@ -11,7 +11,7 @@ add_library(secp256k1_precomputed OBJECT EXCLUDE_FROM_ALL
 add_library(secp256k1 secp256k1.c $<TARGET_OBJECTS:secp256k1_precomputed>)
 
 add_library(secp256k1_asm INTERFACE)
-if(SECP256K1_ASM STREQUAL "arm")
+if(SECP256K1_ASM STREQUAL "arm32")
   add_library(secp256k1_asm_arm OBJECT EXCLUDE_FROM_ALL)
   target_sources(secp256k1_asm_arm PUBLIC
     asm/field_10x26_arm.s