https://bugs.llvm.org/show_bug.cgi?id=34143
Bug ID: 34143
Summary: Hardfault when dereferencing unaligned float
Product: clang
Version: 4.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: d...@walms.co.uk
CC: llvm-bugs@lists.llvm.org
Code to reproduce:
```
template <typename T> inline T Read (uint8_t* data)
{
auto valuePtr = reinterpret_cast<T*> (data);
auto value = *valuePtr;
return value;
}
static float test = 180.0f;
int main (void)
{
uint8_t* data = new uint8_t[8];
memcpy (data, &test, sizeof (float));
auto value = Read<float> (data);
memcpy (data + 1, &test, sizeof (float));
value = Read<float> (data + 1); // hard fault here!
return value;
}
```
first call to Read will cause an aligned dereferencing of the pointer.
second call will cause an in-aligned deferencing of pointer to float.
second call causes a hard fault.
Wall -c -fshort-enums -ggdb3 -std=c++14 -fno-rtti -fno-exceptions
-mfpu=fpv4-sp-d16 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mfloat-abi=hard
-ffunction-sections -fdata-sections -O1 -target arm-none-eabi -mcpu=cortex-m4
-mthumb
When code is compiled with -O0, it works.
with -01 it uses VLDR instruction which can not be used unaligned.
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