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Add comments about address word offset and the calculation of byte address select mask for WCR. 

llvm-svn: 151305
This commit is contained in:
Johnny Chen 2012-02-23 23:40:58 +00:00
parent b8cbe9cb4f
commit 6476fad669
1 changed files with 18 additions and 2 deletions
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20
lldb/tools/debugserver/source/MacOSX/arm/DNBArchImpl.cpp
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@ -2329,6 +2329,22 @@ DNBArchMachARM::EnableHardwareWatchpoint (nub_addr_t addr, nub_size_t size, bool
// We can only watch up to four bytes that follow a 4 byte aligned address
// per watchpoint register pair. Since we can only watch until the next 4
// byte boundary, we need to make sure we can properly encode this.
// addr_word_offset = addr % 4, i.e, is in set([0, 1, 2, 3])
//
// +---+---+---+---+
// | 0 | 1 | 2 | 3 |
// +---+---+---+---+
// ^
// |
// word address (4-byte aligned) = addr & 0xFFFFFFFC => goes into WVR
//
// examples:
// 1. addr_word_offset = 1, size = 1 to watch a uint_8 => byte_mask = (0b0001 << 1) = 0b0010
// 2. addr_word_offset = 2, size = 2 to watch a uint_16 => byte_mask = (0b0011 << 2) = 0b1100
//
// where byte_mask goes into WCR[8:5]
uint32_t addr_word_offset = addr % 4;
DNBLogThreadedIf(LOG_WATCHPOINTS, "DNBArchMachARM::EnableHardwareWatchpoint() - addr_word_offset = 0x%8.8x", addr_word_offset);
@ -2348,10 +2364,10 @@ DNBArchMachARM::EnableHardwareWatchpoint (nub_addr_t addr, nub_size_t size, bool
for (i=0; i<num_hw_watchpoints; ++i)
{
if ((m_state.dbg.__wcr[i] & WCR_ENABLE) == 0)
break; // We found an available hw breakpoint slot (in i)
break; // We found an available hw watchpoint slot (in i)
}
// See if we found an available hw breakpoint slot above
// See if we found an available hw watchpoint slot above
if (i < num_hw_watchpoints)
{
// Make the byte_mask into a valid Byte Address Select mask