[libunwind] Add missing alloca.h include

[ldionne]

Summary

At the moment we list a set of specifric platforms for which we use alloca for
_LIBUNWIND_REMEMBER_ALLOC. We assume that on those platforms alloca is already
provided somehow. This assumption turns out to be wrong sometimes. In
particular a baremetal system using picolibc is assumed to provide aloca, but
doesn't when compiled with pedantic/without gnu extentions.

This changes the behaviour by looking for different ways an alloca
implementation could be provided and using it when found. If no alloca can be
found we revert back to using malloc.

[mstorsjo]

alloca.h isn’t a standard header, and not all those platforms included in the ifdef do have a header with that name (even if they have the alloca function/macro provided somehow by some other header).

See earlier discussion in e.g. https://reviews.llvm.org/D149635.

[StevenvdSchoot]

In D154490#4473310, @mstorsjo wrote:

alloca.h isn’t a standard header, and not all those platforms included in the ifdef do have a header with that name (even if they have the alloca function/macro provided somehow by some other header).

See earlier discussion in e.g. https://reviews.llvm.org/D149635.

Ahh, sorry I missed that PR.
I see there has been no activity on that issue since May 10. Based on the comments there, I created a new version.

[mstorsjo]

libunwind/src/config.h

26

Please avoid changing the indentation of the otherwise unchanged lines (throughout the whole patch).

[StevenvdSchoot]

Undid formatting changes

[ldionne]

[Github PR transition cleanup]

Abandoning in favour of picking up D149635, where we suggested just using __builtin_alloca. All supported compilers should support it.

libunwind/src/config.h

 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
 
 #include <__libunwind_config.h>
 
 // Platform specific configuration defines.
 #ifdef __APPLE__
-  #if defined(FOR_DYLD)
-    #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND 1
-  #else
-    #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND 1
-    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
-  #endif
 #elif defined(_WIN32)
-  #ifdef __SEH__
-    #define _LIBUNWIND_SUPPORT_SEH_UNWIND 1
-  #else
-    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
-  #endif
 #elif defined(_LIBUNWIND_IS_BAREMETAL)
-  #if !defined(_LIBUNWIND_ARM_EHABI)
-    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
-    #define _LIBUNWIND_SUPPORT_DWARF_INDEX 1
-  #endif
 #elif defined(__BIONIC__) && defined(_LIBUNWIND_ARM_EHABI)
-  // For ARM EHABI, Bionic didn't implement dl_iterate_phdr until API 21. After
-  // API 21, dl_iterate_phdr exists, but dl_unwind_find_exidx is much faster.
-  #define _LIBUNWIND_USE_DL_UNWIND_FIND_EXIDX 1
 #elif defined(_AIX)
 // The traceback table at the end of each function is used for unwinding.
 #define _LIBUNWIND_SUPPORT_TBTAB_UNWIND 1
 #else
-  // Assume an ELF system with a dl_iterate_phdr function.
-  #define _LIBUNWIND_USE_DL_ITERATE_PHDR 1
-  #if !defined(_LIBUNWIND_ARM_EHABI)
-    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
-    #define _LIBUNWIND_SUPPORT_DWARF_INDEX 1
-  #endif
 #endif
 
 #if defined(_LIBUNWIND_HIDE_SYMBOLS)
-  // The CMake file passes -fvisibility=hidden to control ELF/Mach-O visibility.
-  #define _LIBUNWIND_EXPORT
-  #define _LIBUNWIND_HIDDEN
 #else
-  #if !defined(__ELF__) && !defined(__MACH__) && !defined(_AIX)
-    #define _LIBUNWIND_EXPORT __declspec(dllexport)
-    #define _LIBUNWIND_HIDDEN
-  #else
-    #define _LIBUNWIND_EXPORT __attribute__((visibility("default")))
-    #define _LIBUNWIND_HIDDEN __attribute__((visibility("hidden")))
-  #endif
 #endif
 
 #define STR(a) #a
 #define XSTR(a) STR(a)
 #define SYMBOL_NAME(name) XSTR(__USER_LABEL_PREFIX__) #name
 
 #if defined(__APPLE__)
 #if defined(_LIBUNWIND_HIDE_SYMBOLS)
#if defined(__i386__) || defined(__x86_64__) || defined(__powerpc__) ||        \
     (!defined(__APPLE__) && defined(__arm__)) || defined(__aarch64__) ||       \
     defined(__mips__) || defined(__riscv) || defined(__hexagon__) ||           \
     defined(__sparc__) || defined(__s390x__) || defined(__loongarch__)
 #if !defined(_LIBUNWIND_BUILD_SJLJ_APIS)
 #define _LIBUNWIND_BUILD_ZERO_COST_APIS
 #endif
 #endif
 
+#if defined(__has_builtin)
+#define _LIBUNWIND_HAS_BUILTIN(x) __has_builtin(x)
+#else
+#define _LIBUNWIND_HAS_BUILTIN(x) 0
+#endif
+
+#if defined(__has_include)
+#define _LIBUNWIND_HAS_INCLUDE(x) __has_include(x)
+#else
+#define _LIBUNWIND_HAS_INCLUDE(x) 0
+#endif
+
 #ifndef _LIBUNWIND_REMEMBER_HEAP_ALLOC
-#if defined(_LIBUNWIND_REMEMBER_STACK_ALLOC) || defined(__APPLE__) ||          \
-    defined(__linux__) || defined(__ANDROID__) || defined(__MINGW32__) ||      \
-    defined(_LIBUNWIND_IS_BAREMETAL)
+
+#if _LIBUNWIND_HAS_BUILTIN(__builtin_alloca)
+#define _LIBUNWIND_REMEMBER_ALLOC(_size) __builtin_alloca(_size)
+#define _LIBUNWIND_REMEMBER_FREE(_ptr)                                         \
+  do {                                                                         \
+  } while (0)
+#elif defined(alloca)
+#define _LIBUNWIND_REMEMBER_ALLOC(_size) alloca(_size)
+#define _LIBUNWIND_REMEMBER_FREE(_ptr)                                         \
+  do {                                                                         \
+  } while (0)
+#elif _LIBUNWIND_HAS_INCLUDE(<alloca.h>)
+#include <alloca.h>
 #define _LIBUNWIND_REMEMBER_ALLOC(_size) alloca(_size)
 #define _LIBUNWIND_REMEMBER_FREE(_ptr)                                         \
   do {                                                                         \
   } while (0)
 #elif defined(_WIN32)
 #define _LIBUNWIND_REMEMBER_ALLOC(_size) _malloca(_size)
 #define _LIBUNWIND_REMEMBER_FREE(_ptr) _freea(_ptr)
 #define _LIBUNWIND_REMEMBER_CLEANUP_NEEDED
#define _LIBUNWIND_LOG0(msg) do {                                              \
   } while (0)
 #define _LIBUNWIND_LOG(msg, ...) do {                                          \
     fprintf(stderr, "libunwind: " msg "\n", __VA_ARGS__);                      \
     fflush(stderr);                                                            \
   } while (0)
 #endif
 
 #if defined(NDEBUG)
-  #define _LIBUNWIND_LOG_IF_FALSE(x) x
 #else
   #define _LIBUNWIND_LOG_IF_FALSE(x)                                           \
     do {                                                                       \
       bool _ret = x;                                                           \
       if (!_ret)                                                               \
         _LIBUNWIND_LOG("" #x " failed in %s", __FUNCTION__);                   \
-    } while (0)
 #endif
 
 // Macros that define away in non-Debug builds
 #ifdef NDEBUG
-  #define _LIBUNWIND_DEBUG_LOG(msg, ...)
-  #define _LIBUNWIND_TRACE_API(msg, ...)
-  #define _LIBUNWIND_TRACING_UNWINDING (0)
-  #define _LIBUNWIND_TRACING_DWARF (0)
-  #define _LIBUNWIND_TRACE_UNWINDING(msg, ...)
-  #define _LIBUNWIND_TRACE_DWARF(...)
 #else
-  #ifdef __cplusplus
-    extern "C" {
-  #endif
     extern  bool logAPIs(void);
     extern  bool logUnwinding(void);
     extern  bool logDWARF(void);
-  #ifdef __cplusplus
-    }
-  #endif
   #define _LIBUNWIND_DEBUG_LOG(msg, ...)  _LIBUNWIND_LOG(msg, __VA_ARGS__)
   #define _LIBUNWIND_TRACE_API(msg, ...)                                       \
     do {                                                                       \
       if (logAPIs())                                                           \
         _LIBUNWIND_LOG(msg, __VA_ARGS__);                                      \
-    } while (0)
-  #define _LIBUNWIND_TRACING_UNWINDING logUnwinding()
-  #define _LIBUNWIND_TRACING_DWARF logDWARF()
   #define _LIBUNWIND_TRACE_UNWINDING(msg, ...)                                 \
     do {                                                                       \
       if (logUnwinding())                                                      \
         _LIBUNWIND_LOG(msg, __VA_ARGS__);                                      \
-    } while (0)
   #define _LIBUNWIND_TRACE_DWARF(...)                                          \
     do {                                                                       \
       if (logDWARF())                                                          \
         fprintf(stderr, __VA_ARGS__);                                          \
-    } while (0)
 #endif
 
 #ifdef __cplusplus
 // Used to fit UnwindCursor and Registers_xxx types against unw_context_t /
 // unw_cursor_t sized memory blocks.
 #if defined(_LIBUNWIND_IS_NATIVE_ONLY)
 # define COMP_OP ==
 #else
 # define COMP_OP <=
 #endif
 template <typename _Type, typename _Mem>
 struct check_fit {
   template <typename T>
   struct blk_count {
     static const size_t count =
         (sizeof(T) + sizeof(uint64_t) - 1) / sizeof(uint64_t);
   };
   static const bool does_fit =
       (blk_count<_Type>::count COMP_OP blk_count<_Mem>::count);
 };
 #undef COMP_OP
 #endif // __cplusplus
 
 #endif // LIBUNWIND_CONFIG_H