Catching memory corruption "in the act"

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trixie

Re: Catching memory corruption "in the act"

Posted on: 3/30 6:00 #21

Amigans Defender

@msteed

Quote:

I normally use the CLIENT "ProgramName" option with MemGuard, so only the program I'm testing is monitored;

I've tried that of course; crashes anyway

The Rear Window blog

AmigaOne X5000 @ 2GHz / 4GB RAM / Radeon RX 560 / ESI Juli@ / AmigaOS 4.1 Final Edition
SAM440ep-flex @ 667MHz / 1GB RAM / Radeon 9250 / AmigaOS 4.1 Final Edition

LiveForIt

Re: Catching memory corruption "in the act"

Posted on: 3/30 9:35 #22

Home away from home

@trixie

Are you speaking of a client / server option, so it sends TCP packets Well as long as OS does not completely freezes because of corruption.

(NutsAboutAmiga)

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and other tools and apps.

BSzili

Re: Catching memory corruption "in the act"

Posted on: Today 5:42 #23

Quite a regular

Back to the original topic, I was finally able to try the MMU protection method. Here's my example program:


#include <proto/exec.h>



#include <stdio.h>

#include <stdlib.h>



#define BUFFER_SIZE 48

#define MEM_ALIGN_SIZE 4096

#define MEM_GUARD_SIZE 4096



void *AllocMemory(int size, int protect)

{

    UBYTE *ptr = IExec->AllocVecTags(MEM_GUARD_SIZE + size,

        AVT_Type,              MEMF_PRIVATE,

        AVT_Alignment,         MEM_ALIGN_SIZE,

        TAG_END);

    if (!ptr) return NULL;



    if (protect)

    {

        struct MMUIFace *IMMU = (struct MMUIFace *)IExec->GetInterface((struct Library *)SysBase, (CONST_STRPTR)"MMU", 1, NULL);

        ULONG attrs = IMMU->GetMemoryAttrs(ptr, 0);

        IMMU->SetMemoryAttrs(ptr, MEM_GUARD_SIZE, (attrs | MEMATTRF_READ_ONLY));

        IExec->DropInterface((struct Interface *)IMMU);

    }



    return ptr ? (ptr + MEM_GUARD_SIZE) : NULL;

}



void FreeMemory(void *block)

{

    if (!block) return;

    UBYTE *ptr = (UBYTE *)block;

    IExec->FreeVec(ptr - MEM_GUARD_SIZE);

}



int main(int argc, char *argv[])

{

    BOOL protect = (argc > 1) ? atoi(argv[1]) : 0;

    printf("allocating %d bytes protect %d\n", BUFFER_SIZE, protect);

    UBYTE *buf = AllocMemory(BUFFER_SIZE, protect);

    if (!buf)

    {

        printf("allocation failed\n");

        return 1;

    }



    printf("valid writes...\n");

    for (int i = 0; i < BUFFER_SIZE; i++)

    {

        buf[i] = 0xFF;

    }

    printf("invalid write...\n");

    buf[-1] = 0xFF;

    printf("invalid writes...\n");

    for (int i = 0; i < MEM_GUARD_SIZE; i++)

    {

        buf[-i] = 0xFF;

    }



    printf("freeing memory\n");

    FreeMemory(buf);



    return 0;

}

This works in my simple test case, but there's one catch: the actual project does a metric ton of small memory allocations. The 4KB overhead plus the alignment requirement makes the memory fragmented to the point where the allocations start to fail, even with a 512MB Z3 RAM expansion. I tried smaller guard blocks while keeping the alignment as 4KB, but that ended up causing all sorts of freezes and crashes.
I guess my only option is Linux? :(

This is just like television, only you can see much further.

Georg

Re: Catching memory corruption "in the act"

Posted on: Today 6:48 #24

Just popping in

Quote:

I guess my only option is Linux? :(

If a PPC binary of the program exists: you can run 32bit or 64bit PPC big endian programs on little endian 64 bit x64 Linux with qemu user mode emulatation ("qemu-ppc" instead of "qemu-system-ppc"). You don't need to have PPC Linux installed, only download some Linux PPC iso and loop-mount it (and likely some filesytem image inside that as well) so you can tell qemu with "-L" where to pick up some PPC versions of libs the PPC binary needs.

I recently tried this with old (2011) version of 32 bit AROS PPC hosted on Linux version and it works pretty well. On old PC here (10 years old?) it "boots" into WB in 3 to 4 seconds (x86 AROS hosted debug version "boots" in maybe 0.5 seconds).

BSzili

Re: Catching memory corruption "in the act"

Posted on: Today 16:17 #25

Quite a regular

That sounds promising, because I had a terrible luck trying to install recent PPC Linux distros in QEMU. The project can be built for i386 Linux I think I could make a PPC executable with reasonable effort.
I saw that GDB is supported via user mode emulation, but I guess I'm going to need Valgrind too to catch the illegal writes outside the allocated blocks?

This is just like television, only you can see much further.

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