32-bits offset issue preventing module to load,

* 32-bits offset issue preventing module to load,
@ 2019-10-28 16:57 Romain Dolbeau
  2019-10-29 10:50 ` Aurelien Jarno
  0 siblings, 1 reply; 2+ messages in thread
From: Romain Dolbeau @ 2019-10-28 16:57 UTC (permalink / raw)
  To: Paul Walmsley, Palmer Dabbelt, Albert Ou; +Cc: linux-riscv, romain

Hello,

I have a Fedora RISC-V running fine in QEMU, using packaged kernel "5.4.0-0.rc4.git0.300.1.riscv64.fc32.riscv64".
Some modules won't load, such as openvswitch:

#####
$ sudo modprobe openvswitch ; dmesg | tail -1
modprobe: ERROR: could not insert 'openvswitch': Invalid argument
[  227.833317] openvswitch: target ffffffe0000d1fd8 can not be addressed by the 32-bit offset from PC = 00000000bcd11221
#####

The message is explicit, a 32-bits offset is not enough to access the data @ 0xffffffe0000d1fd8 from 0x00000000bcd11221. The relevant (I think) part of the System.map is:

#####
/usr/src/kernels/5.4.0-0.rc4.git0.300.1.riscv64.fc32.riscv64/System.map:ffffffe0000d1fd8 D __init_end
/usr/src/kernels/5.4.0-0.rc4.git0.300.1.riscv64.fc32.riscv64/System.map:ffffffe0000d1fd8 D __per_cpu_end
/usr/src/kernels/5.4.0-0.rc4.git0.300.1.riscv64.fc32.riscv64/System.map:ffffffe0000d1fd8 T _stext
/usr/src/kernels/5.4.0-0.rc4.git0.300.1.riscv64.fc32.riscv64/System.map:ffffffe0000d1fd8 T _text
/usr/src/kernels/5.4.0-0.rc4.git0.300.1.riscv64.fc32.riscv64/System.map:ffffffe0000d1fd8 t trace_initcall_finish_cb
#####

As far as I can tell, the issue lies with the fact that the offending modules are using per-cpu data, an uncommon occurrence in modules (according to 'grep' ;-) ). I have a small reproducer that fails in the same way on my QEMU machine. It's small enough I can put it inline at the end of this mail (sometimes attachment gets stripped...). I get the same error in dmesg when trying to load it:

[  585.528200] toto: target ffffffe0000d1fd8 can not be addressed by the 32-bit offset from PC = 00000000465adc9c

The test code works just fine on x86-64, I couldn't try another architecture.

Cordially,

Romain Dolbeau

##### toto.c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>

#include <linux/kmod.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("None will accept the blame");
MODULE_DESCRIPTION("Bug reproducer");
MODULE_VERSION("0.01");

static DEFINE_PER_CPU(uint64_t[2], test_data);

static int __init toto_init(void) {
        int i;
        printk(KERN_INFO "Hello, World!\n");
        for_each_possible_cpu(i) {
            uint64_t *data = per_cpu(test_data, i);
            printk(KERN_INFO "data for %d is %p\n", i, data);
        }
        return 0;
}

static void __exit toto_exit(void) {
         printk(KERN_INFO "Goodbye, World!\n");
}

module_init(toto_init);
module_exit(toto_exit);
##### Makefile
obj-m += toto.o

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

test:
        sudo insmod toto.ko && sudo rmmod toto || true
        sudo dmesg | tail -5
#####

-- 
Romain Dolbeau

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