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73416ba
(Get the code!)
Created attachment 28483
Test case
If the following conditions are true, a constant pool is placed too far from an LDR instruction accessing it:
- Compiling to Thumb2.
- There is no unconditional branch within 4k of the LDR instruction.
- At least one of:
* The LDR instruction is not at a 4-byte aligned address.
* There is an instruction boundary 4094 bytes from the value of PC
at the LDR.
The problem here is twofold:
1. The base address of a PC-relative LDR in Thumb2 is the address of the
instruction plus 4, rounded down to a multiple of 4. The calculation
for the valid range fails to take this rounding into account.
2. The constant pool is (rightly) 4-byte aligned. When scanning the
instructions for a suitable location, the possible need for padding
is not considered.
The problem can be seen by compiling the attached preprocessed source using flags "-mthumb -march=armv7-a -mfpu=vfpv3-d16 -mfloat-abi=hard -O0 -fPIC".