erm wat? malloc error

I got this after compiling my program:

Code:

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mitsy.elf: malloc.c:2401: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || ((unsigned long) (old_size) >= MINSIZE && prev_inuse (old_top) && ((unsigned long) old_end & (pagesize - 1)) == 0)' failed.
Aborted (core dumped)

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Not quite sure what is casuing this, I have only one instance of calloc being used in this function

Code:

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void* InitSegment(
        segment_t *this, segment_t *prev,
        u16 upto, char const *txt, u16 Tsize ) {
        this->pos = prev ? prev->pos + prev->mem.size : 0;
        this->mem.buff = calloc( upto, Tsize );
        if ( !this->mem.buff ) {
                memset( this, 0, sizeof(segment_t) );
                return NULL;
        }
        this->mem.size = upto * Tsize;
        this->mem.upto = upto;
        this->mem.used = 0;
        this->txt = txt;
        return this->mem.buff;
}

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malloc & realloc are never used so I don't even understand how this error can occur, I get that calloc probably uses malloc under the hood but how does an error like above even occur?

Edit: Shoulda mentioned this before but since the edit it now only says segmentation fault, trying to find GUI debugger mode for geany, the only one I found so far has a dead link

Maybe you write to a part of memory you shouldn't, thus corrupting the memory block's metadata?

Ended up using codeblocks depsite it's clunkiness and poorly documented variables, anyways the segfault is appearing here:

Code:

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phent = &phead[1];
phent->p_type = ELPH_PT_LOAD; // < This line is the apparent cause

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Can't imagin how though, phead is initialised to 2 program headers and a failure leads to freeing allocated memory and jumping to the exit

Still don't know what caused it but managed to resolve the error by changing from multiple allocations to a big allocation after calculating the need memory:

Code:

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void* Setup64( segment_t *segv, u16 segments, u16 symbols, u16 headers, ... ) {
        u16 size = 1, i = 0;
        segment_t *ehead_seg = &segv[SEG_EHEAD];
        segment_t *shead_seg = &segv[SEG_SHEAD];
        segment_t *spool_seg = &segv[SEG_SPOOL];
        segment_t *names_seg = &segv[SEG_NAMES];
        segment_t *phead_seg = &segv[SEG_PHEAD];
        segment_t *coded_seg = &segv[SEG_CODED];
        segment_t *this, *prev;
        char const *str = NULL;
        char *pool;
        va_list args;
        va_start( args, headers );
        str = va_arg( args, char const * );
        while ( str ) {
                segoffsetv[i] = strlen( str ) + 1;
                size += segoffsetv[i++];
                spool_seg->mem.upto++;
                spool_seg->mem.used++;
                str = va_arg( args, char const * );
        } size += 1;
        va_end( args );
        ehead_seg->mem.size = sizeof(ehead64_t);
        ehead_seg->mem.upto = ehead_seg->mem.used = 1;
        shead_seg->mem.size = sizeof(shead64_t) * segments;
        shead_seg->mem.upto = segments;
        spool_seg->mem.size = size;
        names_seg->mem.size = sizeof(named64_t) * symbols;
        names_seg->mem.upto = symbols;
        phead_seg->mem.size = sizeof(phead64_t) * headers;
        phead_seg->mem.upto = headers;
        coded_seg->mem.size = sizeof(begin_t);
        coded_seg->mem.upto = coded_seg->mem.used = 1;
        for ( i = 0, size = 0; i < SEG_COUNT; ++i ) {
                size += segv[i].mem.size;
        }
        ehead_seg->mem.buff = calloc( 1, size );
        if ( !ehead_seg->mem.buff ) return NULL;
        for ( i = 1; i < SEG_COUNT; ++i ) {
                prev = &segv[i-1];
                this = &segv[i];
                this->pos = prev->pos + prev->mem.size;
                this->mem.buff = &(((char*)ehead_seg->mem.buff)[this->pos]);
        }
        va_start( args, headers );
        str = va_arg( args, char const * );
        pool = (char*)spool_seg->mem.buff;
        i = 0;
        while ( str ) {
                strcpy( &pool[segoffsetv[i++]], str );
                str = va_arg( args, char const * );
        } size += 1;
        va_end( args );
        return ehead_seg->mem.buff;
}

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