Add a work around for the unaligned access and add some notes on what was happening

1 files changed, 19 insertions, 2 deletions

diff --git a/parser.c b/parser.c
index 6d3ae2e..5b4779a 100644
--- a/parser.c
+++ b/parser.c
@@ -1274,8 +1274,25 @@ static int Go_Float_eprom51(gchar** response, int channel, char *loc_string,char
 		return OK;
 		break;
 
-	case query_param:
-		return query_float(response, *(float *)(&globals.Flash.flash_start + eprom_loc));
+	case query_param:{
+		// The basic issue here is that this pointer isn't aligned. Which
+		// should actually be a problem as ARMv7 has unaligned access support
+		// and it's hardcoded to be on.. the issue is that not all instructions
+		// can do unaliged accesses and the previous code generated one of those
+		// instructions. The kernel traps the access and kills the process.
+		// You should see something like this in dmesg:
+		// [494223.471575] Alignment trap: not handling instruction edd37a00 at [<00011d12>]
+		// [494223.479380] Unhandled fault: alignment exception (0x001) at 0x00050d66
+		//
+		// I use memcpy here to copy the variable out into a temp
+		// variable on the stack which is aligned.
+		// There are probably other bits of code that will trigger this because of
+		// the use of offsets into the struct.. It might be an idea to write some macros
+		// for pushing and pulling bits from the struct.
+		float temp;
+		memcpy(&temp, (float *)(&globals.Flash.flash_start + eprom_loc),sizeof(float));
+		return query_float(response, temp);
+	}
 		break;
 
 	default: