On Tue, 2024-05-28 at 11:24 +0200, Alejandro Colomar wrote: > From what I can see, glibc does no magic to set unspecified parameters > to 0, so this means passing '0' results in Undefined Behavior. On most targets where Glibc implements prctl in assembly (not C), the C standard does not apply at all so there's no Undefined Behavior. There's just "expected" and "unexpected" behaviors. So on 32-bit targets (both long and int are 32-bit) there's no problem. On targets like riscv64 and loongarch64 the ABI mandates a sign- extension on parameters narrower than a GPR, so there's no problem as well. x86_64 does not have such a guarantee (as said in https://gcc.gnu.org/PR46942) so yes passing '0' may leave the high 32 bits of the parameter uninitialized and cause problems (at least in theory). -- Xi Ruoyao <xry111@xxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
