arm: fix UB due to missing mode check [PR100311]

Some places in the compiler iterate over all the fixed registers to
check if that register can be used in a particular mode.  The idiom is
to iterate over the register and then for that register, if it
supports the current mode to check all that register and any
additional registers needed (HARD_REGNO_NREGS).  If these two checks
are not fully aligned then it is possible to generate a buffer overrun
when testing data objects that are sized by the number of hard regs in
the machine.

The VPR register is a case where these checks were not consistent and
because this is the last HARD register the result was that we ended up
overflowing the fixed_regs array.

gcc:
	PR target/100311
	* config/arm/arm.c (arm_hard_regno_mode_ok): Only allow VPR to be
	used in HImode.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 6641e3fb4dcb0e66b386439792274b650c537691..0371d9818fd83512113ed4f46742979cc016b516 100644 (file)
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -25269,7 +25269,7 @@ arm_hard_regno_mode_ok (unsigned int regno, machine_mode mode)
     return false;
 
   if (IS_VPR_REGNUM (regno))
-    return true;
+    return mode == HImode;
 
   if (TARGET_THUMB1)
     /* For the Thumb we only allow values bigger than SImode in