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Fix operator[] for vector2d and vector3d being potentially UB (#15977)

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We don't have a C++ expert on hand, but taking a pointer to one member
and expecting to access another by an offset is very fishy:
- for one, there could theoretically be padding
- the compiler might assume that we are only writing to that first member

The new code has shown to be free for constant parameter values.
Non-constant ones cause the assembly to have branches (why?), but we don't
use that much.
This commit is contained in:
sfan5
2025-04-08 22:25:45 +02:00
committed by GitHub
parent 46db688cc8
commit a00b9cab36
5 changed files with 39 additions and 30 deletions
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16
irr/include/irrTypes.h
View File

@@ -85,6 +85,22 @@ typedef char fschar_t;
/** prefer to use the override keyword for new code */
#define _IRR_OVERRIDE_ override
// Invokes undefined behavior for unreachable code optimization
// Note: an assert(false) is included first to catch this in debug builds
#if defined(__cpp_lib_unreachable)
#include <utility>
#define IRR_CODE_UNREACHABLE() do { _IRR_DEBUG_BREAK_IF(1) std::unreachable(); } while(0)
#elif defined(__has_builtin)
#if __has_builtin(__builtin_unreachable)
#define IRR_CODE_UNREACHABLE() do { _IRR_DEBUG_BREAK_IF(1) __builtin_unreachable(); } while(0)
#endif
#elif defined(_MSC_VER)
#define IRR_CODE_UNREACHABLE() do { _IRR_DEBUG_BREAK_IF(1) __assume(false); } while(0)
#endif
#ifndef IRR_CODE_UNREACHABLE
#define IRR_CODE_UNREACHABLE() (void)0
#endif
//! creates four CC codes used in Irrlicht for simple ids
/** some compilers can create those by directly writing the
code like 'code', but some generate warnings so we use this macro here */

16
irr/include/vector2d.h
View File

@@ -131,16 +131,20 @@ public:
T &operator[](u32 index)
{
_IRR_DEBUG_BREAK_IF(index > 1) // access violation
return *(&X + index);
switch (index) {
case 0: return X;
case 1: return Y;
default: IRR_CODE_UNREACHABLE();
}
}
const T &operator[](u32 index) const
{
_IRR_DEBUG_BREAK_IF(index > 1) // access violation
return *(&X + index);
switch (index) {
case 0: return X;
case 1: return Y;
default: IRR_CODE_UNREACHABLE();
}
}
//! sort in order X, Y.

18
irr/include/vector3d.h
View File

@@ -117,16 +117,22 @@ public:
T &operator[](u32 index)
{
_IRR_DEBUG_BREAK_IF(index > 2) // access violation
return *(&X + index);
switch (index) {
case 0: return X;
case 1: return Y;
case 2: return Z;
default: IRR_CODE_UNREACHABLE();
}
}
const T &operator[](u32 index) const
{
_IRR_DEBUG_BREAK_IF(index > 2) // access violation
return *(&X + index);
switch (index) {
case 0: return X;
case 1: return Y;
case 2: return Z;
default: IRR_CODE_UNREACHABLE();
}
}
//! sort in order X, Y, Z.