Technorama

An omnibus of tech posts by a Futurologist on software development primarily.

Monday 6 May 2024

The Next Pandemic

Given we've had coronavirus circulating for thousands of years, and various outbreaks like SARS (2002), MERS (2012) and COVID (2019) it looks like given the global nature of travel we'll have another epidemic like SARS or a pandemic like COVID within a range of 6-10 years, the confidence of this date prediction is not high.

posted by 東京 # 19:25 0 Comments

Thursday 12 October 2023

Secure sandboxes

Seems easy, iPhone keeps getting malware owned by faulty image files.

Sandbox decoders

Run decompressors in a micro sandboxed VM. It it doesn't finish decoding and outputting an uncompressed bitmap file to a ramdrive within one second, just kill the sandbox. Saves being exploited. (Unless the sandbox VM can also be jailbreaked)

Compile the process in the sandbox with AddressSanitizer.

Have a system to automatically upload any coredumps from the sandbox crashes, either then, or after a reboot.

Probably those creating the security exploits will test on real devices a few times before they get a working crack. That gives you chance to get the coredump and backtrace.

posted by 東京 # 13:25 0 Comments

Wednesday 6 September 2023

gcc attribute nonnull considered harmful

gcc function attributes allow optimizer hints, set attribute nonnull and the optimizer will know it is never going to be a nullptr - so it will remove all nullptr checks!

This is often not what is expected by the humble programmer.

posted by 東京 # 23:10 0 Comments

Monday 10 April 2023

Chromium debug build with symbols

Navigate here

Click "Last Modified" heading

Then get the build folder number from the file LAST_CHANGE

posted by 東京 # 20:54 0 Comments

Tuesday 21 February 2023

Custom C/C++ assert example with file line and column information

// -fanalyzer -DNDEBUG -Wno-analyzer-use-of-uninitialized-value

#include <string>
#include <iostream>
#include <string_view>
#include <source_location>

// Pass const std::source_location location = std::source_location::current()
#if NDEBUG
#define myassert(x, s, l)
#else
#define myassert(x, s, l) if(!x)  {printf("%s:%d:%d %s %s\n", l.file_name(), l.line(), l.column(), l.function_name(), s); fflush(stdout); abort();}
#endif

#define TRIGGER_NULLPTR_WARNING 1

std::string make_std_string(const char * const str, const std::source_location location =
               std::source_location::current())
{
    myassert((nullptr != str), "nullptr dereference", location);

#if TRIGGER_NULLPTR_WARNING
    // This line ensures: warning: dereference of NULL '0' [CWE-476] [-Wanalyzer-null-dereference]
    char b = *str; 
#endif

    std::string s(str);
#if TRIGGER_NULLPTR_WARNING
    s[0] = b;
#endif

    return s;
}

int main()
{
    const char * a = NULL;
    std::string result = make_std_string(a);
    std::cout << result;
}

posted by 東京 # 21:39 0 Comments

Thursday 16 February 2023

Use macros to contatenate file and line info into a string so easier to see when debugging particular issues with unique info per function.

Unfortunately __FUNCTION__ doesn't work this way though.

#define xto_str(s) to_str(s)

#define to_str(s) #s

int main()
{
const char * s = __FILE__ ":" xto_str(__LINE__);
__builtin_printf(s);
}

.LC0:
        .string "/app/example.cpp:__PRETTY_FUNCTION__"
main:
        subq    $8, %rsp
        movl    $.LC0, %edi
        xorl    %eax, %eax
        call    printf
        xorl    %eax, %eax
        addq    $8, %rsp
        ret

posted by 東京 # 13:51 0 Comments

Wednesday 1 February 2023

Safe C/C++

// Example showing usual way to check parameters are valid to avoid crashing in
// a Release build, and an assert() for a Debug build.

// Some might argue that assert() creates different behaviour in a DEBUG build.
// It means the error handling will never be exercised in a DEBUG build that
// does abort() core dump.
// testsuite must be run in a RELEASE build, to be sure the error handling
// is exercised and good coverage.
// Of course, also application integration tests would run in RELEASE build
// and verify application is fully working.
// It is also fine to leave out the assert() and can verify test suite results
// in a DEBUG build then

#include <assert.h>
#include <stddef.h>
#include <stdio.h>

int example_if(const char * str)
{
    assert(str);

    if(NULL == str)
    {
        return -1;
    }
    else
    {
        printf("%s\n", str);
    }

    return 0;
}

int main()
{
    example_if(NULL);
}

posted by 東京 # 21:53 0 Comments

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