Can't take address of interrupts enabled / disabled function

[rmn30]

I wanted to write some test code along the following lines to get hold of a sealed capability with interrupt disabling sentry type:

[[cheri::interrupt_state(disabled)]] void some_id_function() {
  // blah
}
//...
Capability idSentry = {&some_id_function};

This compiles but I get a linker error:

error: ld.lld: error: Compartment 'isa_test' imports library function 
'__library_export_<mangled name of some_id_function>' 
as cross-compartment call

This is obviously a bit unusual but is it something we could / should support?

[resistor]

@rmn30 Any chance you could post a self-contained test for this?

[rmn30]

The easiest way to reproduce is to edit the hello world example in cheriot-rtos/examples/01.hello_world but I will take a look if I can narrow it down.

[rmn30]

The error is produced at https://github.com/CHERIoT-Platform/llvm-project/blob/cheriot/lld/ELF/Writer.cpp#L3257 , so the question is why is isLibcall false? This comes from a test on the low bit of 'start' from the import table entry so why is that not set?

[rmn30]

If you compile the following:

void (*f)() = 0;

[[cheri::interrupt_state(disabled)]] void id_function(void) {
}

/// Thread entry point.
void __attribute__((cheri_compartment("hello"))) say_hello()
{
        f = &id_function;
}

Like follows:

clang++ -S -std=c++20 -Qunused-arguments -target riscv32-unknown-unknown -mcpu=cheriot -mabi=cheriot -mxcheri-rvc -mrelax -fshort-wchar -nostdinc -Oz -g -ffunction-sections -fdata-sections -fomit-frame-pointer -fno-builtin -fno-exceptions -fno-asynchronous-unwind-tables -fno-c++-static-destructors -fno-rtti -Werror -cheri-compartment=hello -o hello.S hello.cc

and look at the end of the resulting .S you will see the import table entry for id_function:

       .section        .compartment_imports,"aG",@progbits,__library_import_hello__Z11id_functionv,comdat
        .type   __library_import_hello__Z11id_functionv,@object
        .weak   __library_import_hello__Z11id_functionv
        .p2align        3
__library_import_hello__Z11id_functionv:
        .word   __library_export_hello__Z11id_functionv
        .word   0
        .size   __library_import_hello__Z11id_functionv, 8

Apparently the +1 that indicates this is a library import should be in the third last line ( .word __library_export_hello__Z11id_functionv) as like this https://github.com/CHERIoT-Platform/llvm-project/blob/cheriot/llvm/test/CodeGen/RISCV/cheri/cheri-mcu-call-libcall.ll#L44 .