libsframe: handle SFrame FRE start/end IP offsets as unsigned
The SFrame FRE start address (fre_start_addr) is defined as unsigned
32-bit integer, as it is an offset from SFrame FDE function start
address (sfde_func_start_address) and functions only grow upwards
(towards higher addresses).
The SFrame FRE start IP offset is a synonym to the SFrame FRE start
address. The SFrame FRE end IP offset is either the value of the
subsequent FDE start address minus one, if that exists, or the FDE
function size minus one otherwise. Both should therefore be handled
as unsigned 32-bit integer.
In libsframe the "lookup PC" (pc) and SFrame FDE function start address
(sfde_func_start_address) are both signed integers, as they are actually
offsets from the SFrame section. The unsigned FDE start/end IP offsets
may therefore only be safely compared against the offset of the lookup
PC from FDE function start address if the FDE function start address is
lower or equal to the lookup PC, as this guarantees the offset to be
always positive:
Given:
lookup_pc = pc - sframe_addr
sfde_func_start_address = func_start_addr - sframe_addr
If the FDE function start address is lower or equal than the lookup PC,
which both are signed offsets from SFrame section, then the function
start address is also lower or equal to the PC, which are both unsigned:
sfde_func_start_address <= lookup_pc
func_start_addr - sframe_addr <= pc - sframe_addr
func_start_addr <= pc
With that the offset of the lookup PC from FDE function start address
(lookup_pc - sfde_func_start_address) must always be positive, if
FDE function start address is lower or equal to the lookup PC:
lookup_pc - sfde_func_start_address
= pc - sframe_addr - (func_start_addr - sframe_addr)
= pc - func_start_addr
libsframe/
* sframe.c (sframe_find_fre): Define and handle start_ip_offset
and end_ip_offset as unsigned (same as FRE fre_start_addr).
(sframe_fre_check_range_p): Likewise. Define PC offset (from
function start address) as unsigned.
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
1 file changed
