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misc.cc static_assert invalid c++11/14 on macOS #8412

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zeha opened this issue Oct 13, 2019 · 3 comments · Fixed by #8413
Closed

misc.cc static_assert invalid c++11/14 on macOS #8412

zeha opened this issue Oct 13, 2019 · 3 comments · Fixed by #8413

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@zeha
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@zeha zeha commented Oct 13, 2019

  • Program: Authoritative (but I guess all programs)
  • Issue type: Bug report

Short description

this line in misc.cc ...

    static_assert(CMSG_SPACE(sizeof(*pkt)) <= sizeof(*cmsgbuf), "Buffer is too small for in6_pktinfo");

expands to this on macOS:

    static_assert((((__darwin_size_t)((char *)(__darwin_size_t)(sizeof(struct cmsghdr)) + (sizeof(__uint32_t) - 1)) &~ (sizeof(__uint32_t) - 1)) + ((__darwin_size_t)((char *)(__darwin_size_t)(sizeof(*pkt)) + (sizeof(__uint32_t) - 1)) &~ (sizeof(__uint32_t) - 1))) <= sizeof(*cmsgbuf), "Buffer is too small for in6_pktinfo");

This apparently used to compile, but no longer does. Maybe clang got stricter about what it allows inside a constexpr. I've done a quick check if the involved header files have changed, but apparently not.

Compile failure:

misc.cc:893:19: error: static_assert expression is not an integral constant expression
    static_assert(CMSG_SPACE(sizeof(*pkt)) <= sizeof(*cmsgbuf), "Buffer is too small for in6_pktinfo");
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/socket.h:652:33: note: expanded from macro 'CMSG_SPACE'
#define CMSG_SPACE(l)           (__DARWIN_ALIGN32(sizeof(struct cmsghdr)) + __DARWIN_ALIGN32(l))
                                ^
misc.cc:893:19: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/socket.h:652:34: note: expanded from macro 'CMSG_SPACE'
#define CMSG_SPACE(l)           (__DARWIN_ALIGN32(sizeof(struct cmsghdr)) + __DARWIN_ALIGN32(l))
                                 ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/i386/_param.h:43:42: note: expanded from macro '__DARWIN_ALIGN32'
#define       __DARWIN_ALIGN32(p)       ((__darwin_size_t)((char *)(__darwin_size_t)(p) + __DARWIN_ALIGNBYTES32) &~ __DARWIN_ALIGNBYTES32)
                                         ^
misc.cc:912:19: error: static_assert expression is not an integral constant expression
    static_assert(CMSG_SPACE(sizeof(*pkt)) <= sizeof(*cmsgbuf), "Buffer is too small for in_pktinfo");
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/socket.h:652:33: note: expanded from macro 'CMSG_SPACE'
#define CMSG_SPACE(l)           (__DARWIN_ALIGN32(sizeof(struct cmsghdr)) + __DARWIN_ALIGN32(l))
                                ^
misc.cc:912:19: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/socket.h:652:34: note: expanded from macro 'CMSG_SPACE'
#define CMSG_SPACE(l)           (__DARWIN_ALIGN32(sizeof(struct cmsghdr)) + __DARWIN_ALIGN32(l))
                                 ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/i386/_param.h:43:42: note: expanded from macro '__DARWIN_ALIGN32'
#define       __DARWIN_ALIGN32(p)       ((__darwin_size_t)((char *)(__darwin_size_t)(p) + __DARWIN_ALIGNBYTES32) &~ __DARWIN_ALIGNBYTES32)
                                         ^
2 errors generated.

Buried in these errors is this note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression

Some info on constexpr / reinterpret_cast:
https://stackoverflow.com/questions/26200827/getting-around-the-reinterpret-cast-limitation-with-constexpr

Environment

  • Operating system: macOS Catalina
  • Software version: 37c36cc
  • Software source: git

clang version:

Apple clang version 11.0.0 (clang-1100.0.33.8)
Target: x86_64-apple-darwin19.0.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
@zeha
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@zeha zeha commented Oct 13, 2019

TBF, maybe I didn't compile master on macOS since 7f81854, but somehow I doubt this.

@zeha
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@zeha zeha commented Oct 13, 2019

@rgacogne
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@rgacogne rgacogne commented Oct 14, 2019

OK, so macOS somehow managed to implement CMSG_SPACE in a way that isn't a constexpr.. I guess we'll need to define our way out of this..

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