libstdc++: Fix std::format for pointers [PR110239]

The formatter for pointers was casting to uint64_t which sign extends a
32-bit pointer and produces a value that won't fit in the provided
buffer. Cast to uintptr_t instead.

There was also a bug in the __parse_integer helper when converting a
wide string to a narrow string in order to use std::from_chars on it.
The function would always try to read 32 characters, even if the format
string was shorter than that. Fix that bug, and remove the constexpr
implementation of __parse_integer by just using __from_chars_alnum
instead of from_chars, because that's usable in constexpr even in
C++20.

libstdc++-v3/ChangeLog:

	PR libstdc++/110239
	* include/std/format (__format::__parse_integer): Fix buffer
	overflow for wide chars.
	(formatter<const void*, C>::format): Cast to uintptr_t instead
	of uint64_t.
	* testsuite/std/format/string.cc: Test too-large widths.

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 96a1e62ccc8cd5873b0f1d6f92b782aad8051c44..9d5981e4882991cc2cbfb9353d399372030e8722 100644 (file)
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -269,39 +269,26 @@ namespace __format
       if (__first == __last)
        __builtin_unreachable();
 
-      // TODO: use this loop unconditionally?
-      // Most integers used for arg-id, width or precision will be small.
-      if (is_constant_evaluated())
-       {
-         auto __next = __first;
-         unsigned short __val = 0;
-         while (__next != __last && '0' <= *__next && *__next <= '9')
-           {
-             __val = (__val * 10) + (*__next - '0'); // TODO check overflow?
-             ++__next;
-           }
-         if (__next == __first)
-           return {0, nullptr};
-         return {__val, __next};
-       }
-
-      unsigned short __val = 0;
       if constexpr (is_same_v<_CharT, char>)
        {
-         auto [ptr, ec] = std::from_chars(__first, __last, __val);
-         if (ec == errc{})
-           return {__val, ptr};
-         return {0, nullptr};
+         const auto __start = __first;
+         unsigned short __val = 0;
+         // N.B. std::from_chars is not constexpr in C++20.
+         if (__detail::__from_chars_alnum<true>(__first, __last, __val, 10)
+               && __first != __start) [[likely]]
+           return {__val, __first};
        }
       else
        {
+         unsigned short __val = 0;
          constexpr int __n = 32;
          char __buf[__n]{};
-         for (int __i = 0; __i < __n && __first != __last; ++__i)
+         for (int __i = 0; __i < __n && (__first + __i) != __last; ++__i)
            __buf[__i] = __first[__i];
          auto [__v, __ptr] = __format::__parse_integer(__buf, __buf + __n);
          return {__v, __first + (__ptr - __buf)};
        }
+      return {0, nullptr};
     }
 
   template<typename _CharT>
@@ -2118,7 +2105,7 @@ namespace __format
        typename basic_format_context<_Out, _CharT>::iterator
        format(const void* __v, basic_format_context<_Out, _CharT>& __fc) const
        {
-         auto __u = reinterpret_cast<__UINT64_TYPE__>(__v);
+         auto __u = reinterpret_cast<__UINTPTR_TYPE__>(__v);
          char __buf[2 + sizeof(__v) * 2];
          auto [__ptr, __ec] = std::to_chars(__buf + 2, std::end(__buf),
                                             __u, 16);

diff --git a/libstdc++-v3/testsuite/std/format/string.cc b/libstdc++-v3/testsuite/std/format/string.cc
index e421028a873e58d81fc389867c2211ab0dcebff3..d28135ec260b3b0d7e93af481da686b8d7f34774 100644 (file)
--- a/libstdc++-v3/testsuite/std/format/string.cc
+++ b/libstdc++-v3/testsuite/std/format/string.cc
@@ -121,6 +121,11 @@ test_format_spec()
   // Invalid presentation types for strings.
   VERIFY( ! is_format_string_for("{:S}", "str") );
   VERIFY( ! is_format_string_for("{:d}", "str") );
+
+  // Maximum integer value supported for widths and precisions is USHRT_MAX.
+  VERIFY( is_format_string_for("{:65535}", 1) );
+  VERIFY( ! is_format_string_for("{:65536}", 1) );
+  VERIFY( ! is_format_string_for("{:9999999}", 1) );
 }
 
 int main()