From af4eb9e20a6b4d9a5e61d9caaf89daf4c3742150 Mon Sep 17 00:00:00 2001 From: Indu Bhagat Date: Thu, 18 Jul 2024 20:24:00 -0700 Subject: gas: scfi: make scfi_state_restore_reg function more precise When the SCFI machinery detects that a register has been restored from stack, it makes some state changes in the SCFI state object. Prior to the patch, scfi_state_restore_reg () was setting a value of (reg, CFI_IN_REG) for (base, state) respectively. This was causing issues in the cmp_scfi_state () function: - The default state of all (callee-saved) regs at the beginning of function is set to (0, CFI_UNDEFINED). - If a register is saved and restored on some control path, the state of reg is (reg, CFI_IN_REG) on that path. - On another control path where the register was perhaps not used (or saved/restored on stack) remains (0, CFI_UNDEFINED). - The two states should be treated equal, however, at the point in program after the register has been restored. Fix this by resetting the state to (0, CFI_UNDEFINED) in scfi_state_restore_reg (). A testcase (scfi-cfg-4.s) for this is added in a subsequent commit. gas/ * scfi.c (scfi_state_restore_reg): Reset to 0, CFI_UNDEFINED for base, state. --- gas/scfi.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/gas/scfi.c b/gas/scfi.c index 744822d..5898a57 100644 --- a/gas/scfi.c +++ b/gas/scfi.c @@ -223,11 +223,12 @@ scfi_state_restore_reg (scfi_stateS *state, unsigned int reg) gas_assert (state->regs[reg].state == CFI_ON_STACK); gas_assert (state->regs[reg].base == REG_CFA); - state->regs[reg].base = reg; + /* PS: the register may still be on stack much after the restore. Reset the + SCFI state to CFI_UNDEFINED, however, to indicate that the most updated + source of value is register itself from here onwards. */ + state->regs[reg].base = 0; state->regs[reg].offset = 0; - /* PS: the register may still be on stack much after the restore, but the - SCFI state keeps the state as 'in register'. */ - state->regs[reg].state = CFI_IN_REG; + state->regs[reg].state = CFI_UNDEFINED; } /* Identify if the given GAS instruction GINSN saves a register -- cgit v1.1