llvm-project/clang/test/Sema/arm-cmse-no-diag.c

// RUN: %clang_cc1 -triple thumbv8m.base-none-eabi -mcmse -verify -Wno-cmse-union-leak %s
// expected-no-diagnostics

union U { unsigned n; char b[4]; } u;

void (*fn2)(int, union U) __attribute__((cmse_nonsecure_call));

union U xyzzy() __attribute__((cmse_nonsecure_entry)) {
  fn2(0, u);
  return u;
}
[CMSE] Clear padding bits of struct/unions/fp16 passed by value When passing a value of a struct/union type from secure to non-secure state (that is returning from a CMSE entry function or passing an argument to CMSE-non-secure call), there is a potential sensitive information leak via the padding bits in the structure. It is not possible in the general case to ensure those bits are cleared by using Standard C/C++. This patch makes the compiler emit code to clear such padding bits. Since type information is lost in LLVM IR, the code generation is done by Clang. For each interesting record type, we build a bitmask, in which all the bits, corresponding to user declared members, are set. Values of record types are returned by coercing them to an integer. After the coercion, the coerced value is masked (with bitwise AND) and then returned by the function. In a similar manner, values of record types are passed as arguments by coercing them to an array of integers, and the coerced values themselves are masked. For union types, we effectively clear only bits, which aren't part of any member, since we don't know which is the currently active one. The compiler will issue a warning, whenever a union is passed to non-secure state. Values of half-precision floating-point types are passed in the least significant bits of a 32-bit register (GPR or FPR) with the most significant bits unspecified. Since this is also a potential leak of sensitive information, this patch also clears those unspecified bits. Differential Revision: https://reviews.llvm.org/D76369 2020-04-28 23:27:52 +08:00			`// RUN: %clang_cc1 -triple thumbv8m.base-none-eabi -mcmse -verify -Wno-cmse-union-leak %s`
			`// expected-no-diagnostics`

			`union U { unsigned n; char b[4]; } u;`

			`void (*fn2)(int, union U) __attribute__((cmse_nonsecure_call));`

			`union U xyzzy() __attribute__((cmse_nonsecure_entry)) {`
			`fn2(0, u);`
			`return u;`
			`}`