Re: [gem5-users] Error: Tried to read unmapped address

[Andreas Hansson via gem5-users]

Hi Azadeh,

I am not sure what you expected to happen. The “address” you see is probably 
written to memory earlier (as data) and now comes back to you as complete 
gibberish.

Solution: Do not flip bits :-)

Andreas

From: Azadeh Shirvanian via gem5-users 
<gem5-users@gem5.org<mailto:gem5-users@gem5.org>>
Reply-To: Azadeh Shirvanian 
<azadeh.shirvan...@gmail.com<mailto:azadeh.shirvan...@gmail.com>>, gem5 users 
mailing list <gem5-users@gem5.org<mailto:gem5-users@gem5.org>>
Date: Wednesday, 28 January 2015 18:32
To: "gem5-users@gem5.org<mailto:gem5-users@gem5.org>" 
<gem5-users@gem5.org<mailto:gem5-users@gem5.org>>
Subject: [gem5-users] Error: Tried to read unmapped address

Dear all

I am trying to flip every bit of the data, in writeMem, the function in 
src/cpu/simple/timing.cc, so that the data is faulty before it is written to 
the cache.

I am working on X86, classical memory and running in SE mode. I also trace the 
data and the address exchanged between CPU and L1 data cache using CommMonitor. 
That is the reason why I am working on timing.cc.

What I have done:

1. I declared in timing.hh - right after the declaration of writeMem:

void faultInject(uint8_t *data, unsigned size);

2. Then I defined the function in timing.cc to flip every bit of the data:

void
TimingSimpleCPU::faultInject(uint8_t *data, unsigned size)
{   unsigned i,j;
    if (data != NULL)
        for (i=0; i<size; i++)
            for (j=0; j<8; j++)
                data[i] = data[i] ^ (1<<j);
}

3. I called this function inside writeMem, as you can see in green:

Fault
TimingSimpleCPU::writeMem(uint8_t *data, unsigned size,
                          Addr addr, unsigned flags, uint64_t *res)
{
    uint8_t *newData = new uint8_t[size];
    const int asid = 0;
    const ThreadID tid = 0;
    const Addr pc = thread->instAddr();
    unsigned block_size = cacheLineSize();
    BaseTLB::Mode mode = BaseTLB::Write;

    if (data == NULL) {
        assert(flags & Request::CACHE_BLOCK_ZERO);
        // This must be a cache block cleaning request
        memset(newData, 0, size);
    } else {
        faultInject(data, size);
        memcpy(newData, data, size);
    }

After compiling:
scons build/X86/gem5.opt

and running:
build/X86/gem5.opt configs/example/se.py --cpu-type=timing --caches -c 
tests/test-progs/hello/bin/x86/linux/hello > log.txt

I get the following error:

0: system.remote_gdb.listener: listening for remote gdb #0 on port 7000
panic: Tried to read unmapped address 0xffff8000000011bf.
 @ tick 630000
[invoke:build/X86/arch/x86/faults.cc, line 160]
Memory Usage: 631820 KBytes
Program aborted at tick 630000
Aborted (core dumped)

Reading email threads and changing my code did not eventually help. Thus, I 
would be really grateful if anyone could clarify the reason of this problem and 
the solution to it.

Azadeh


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