From e588b294c8c785190307be07ea963f2647301b02 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Martin=20Storsj=C3=B6?= Date: Wed, 12 Mar 2025 23:46:56 +0200 Subject: [PATCH 1/2] [libcxxabi] Use __LDBL_MANT_DIG__ for configuring demangling of long doubles This avoids needing to hardcode the mapping between architectures and their sizes of long doubles. This fixes a case in test_demangle.pass.cpp, that previously failed like this (XFAILed): .---command stdout------------ | Testing 29859 symbols. | _ZN5test01hIfEEvRAcvjplstT_Le4001a000000000000000E_c should be invalid but is not | Got: 0, void test0::h(char (&) [(unsigned int)(sizeof (float) + 0x0.07ff98f7ep-1022L)]) `----------------------------- .---command stderr------------ | Assertion failed: !passed && "demangle did not fail", file libcxxabi/test/test_demangle.pass.cpp, line 30338 `----------------------------- This testcase is defined within // Is long double fp80? (Only x87 extended double has 64-bit mantissa) #define LDBL_FP80 (__LDBL_MANT_DIG__ == 64) ... #if !LDBL_FP80 ... #endif The case failed on x86 architectures with an unusual size for long doubles, as the test expected the demangler to not be able to demangle an 80 bit long double (based on the "_LDBL_MANT_DIG__ == 64" condition in the test). However as the libcxxabi implementation was hardcoded to demangle 80 bit long doubles on x86_64 regardless of the actual size, this test failed (by unexpectedly being able to demangle it). By configuring libcxxabi's demangling of long doubles to match what the compiler specifies, we no longer hit the expected failures in the test_demangle.pass.cpp test on Android on x86. This makes libcxxabi require a GCC-compatible compiler that defines nonstandard defines like __LDBL_MANT_DIG__, but I presume that's already essentially required anyway. --- libcxxabi/src/demangle/ItaniumDemangle.h | 14 ++++++-------- libcxxabi/test/test_demangle.pass.cpp | 4 ---- 2 files changed, 6 insertions(+), 12 deletions(-) diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h index 4122781beb599..328632d193751 100644 --- a/libcxxabi/src/demangle/ItaniumDemangle.h +++ b/libcxxabi/src/demangle/ItaniumDemangle.h @@ -5741,14 +5741,12 @@ struct FloatData template <> struct FloatData { -#if defined(__mips__) && defined(__mips_n64) || defined(__aarch64__) || \ - defined(__wasm__) || defined(__riscv) || defined(__loongarch__) || \ - defined(__ve__) - static const size_t mangled_size = 32; -#elif defined(__arm__) || defined(__mips__) || defined(__hexagon__) - static const size_t mangled_size = 16; -#else - static const size_t mangled_size = 20; // May need to be adjusted to 16 or 24 on other platforms +#if __LDBL_MANT_DIG__ == 113 + static const size_t mangled_size = 32; +#elif __LDBL_MANT_DIG__ == 53 + static const size_t mangled_size = 16; +#else // __LDBL_MANT_DIG__ == 64 + static const size_t mangled_size = 20; #endif // `-0x1.ffffffffffffffffffffffffffffp+16383` + 'L' + '\0' == 42 bytes. // 28 'f's * 4 bits == 112 bits, which is the number of mantissa bits. diff --git a/libcxxabi/test/test_demangle.pass.cpp b/libcxxabi/test/test_demangle.pass.cpp index e9c74f70a094b..abaa787f5432b 100644 --- a/libcxxabi/test/test_demangle.pass.cpp +++ b/libcxxabi/test/test_demangle.pass.cpp @@ -13,10 +13,6 @@ // dd8b266ef. // UNSUPPORTED: using-built-library-before-llvm-20 -// Android's long double on x86[-64] is (64/128)-bits instead of Linux's usual -// 80-bit format, and this demangling test is failing on it. -// XFAIL: LIBCXX-ANDROID-FIXME && target={{i686|x86_64}}-{{.+}}-android{{.*}} - // XFAIL: win32-broken-printf-a-precision #include "support/timer.h" From 8821bca642e3fcf50ab802cd025d11f171f7ede6 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Martin=20Storsj=C3=B6?= Date: Wed, 9 Apr 2025 11:35:18 +0300 Subject: [PATCH 2/2] Actually check the last case, add an #error if the size is unhandled Also check for _MSC_VER for MSVC, as this file is copied and included in the main LLVM build as well. --- libcxxabi/src/demangle/ItaniumDemangle.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h index 328632d193751..b9d17060c04f9 100644 --- a/libcxxabi/src/demangle/ItaniumDemangle.h +++ b/libcxxabi/src/demangle/ItaniumDemangle.h @@ -5743,10 +5743,14 @@ struct FloatData { #if __LDBL_MANT_DIG__ == 113 static const size_t mangled_size = 32; -#elif __LDBL_MANT_DIG__ == 53 +#elif __LDBL_MANT_DIG__ == 53 || defined(_MSC_VER) + // MSVC doesn't define __LDBL_MANT_DIG__, but it has long double equal to + // regular double on all current architectures. static const size_t mangled_size = 16; -#else // __LDBL_MANT_DIG__ == 64 +#elif __LDBL_MANT_DIG__ == 64 static const size_t mangled_size = 20; +#else +#error Unknown size for __LDBL_MANT_DIG__ #endif // `-0x1.ffffffffffffffffffffffffffffp+16383` + 'L' + '\0' == 42 bytes. // 28 'f's * 4 bits == 112 bits, which is the number of mantissa bits.