Long mode can't page above 4 GB

[Je06]

I'm currently developing a C++ kernel using bochs. I managed to setup Long mode, and have a working GDT and paging. The problem I'm running into is that when I try to add anything to virtual memory above 4GB, entry 4+ in the PDP, it doesn't show up when I look at my pages. I've tried 1GB, 2MB, and 4KB pages. Nothing works.

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this->kb_page = 3;
this->mb_pages = 5;
this->kernel_pages = 4;

// Setup PML4, PDP, PD, and KB page tables
this->pages[0][0] = (uint64_t)this->pages[1] | 3;
this->pages[1][0] = (uint64_t)this->pages[2] | 3;
this->pages[2][0] = (uint64_t)this->pages[3] | 3;
    
// Setup Kernel map
this->pages[1][3] = (uint64_t)this->pages[this->kernel_pages] | 3;

// Kernel code/data
this->pages[this->kernel_pages][0] = this->kinfo->kernel_addr | 0x83;
this->pages[this->kernel_pages][1] = this->kinfo->kernel_addr + 0x100000 | 0x83;
    
// Kernel heap
this->pages[this->kernel_pages][2] = 0x200083;
this->pages[this->kernel_pages][3] = 0x400083;
this->pages[this->kernel_pages][4] = 0xa00083;
this->pages[this->kernel_pages][5] = 0xc00083;

// Setup heap
//for (size_t i = 0; i < 64; i++) {
//    this->pages[1][4+i] = (uint64_t)this->pages[this->mb_pages+i] | 3;
//}

this->pages[1][4] = (uint64_t)this->pages[this->mb_pages] | 3;
this->pages[1][5] = 0x83;

with the pages defined as

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typedef uint64_t PageEntry;
typedef PageEntry PageTable[512];
PageTable *pages;

The pages structure is 4KB aligned
And finaly

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set_paging(this->pages[0]);

global set_paging
set_paging:
    mov cr3, rdi
    ret

[nullplan]

My glass ball is in the wash right now, and with the info you provided I cannot be certain, since there is no link to the source code anywhere, nor enough information to make such a determination. However, I bet you cast an address to int at some point, not realizing that this is too small a type.

[Je06]

My glass ball is in the wash right now, and with the info you provided I cannot be certain, since there is no link to the source code anywhere, nor enough information to make such a determination. However, I bet you cast an address to int at some point, not realizing that this is too small a type.

I'm so sorry! I forgot to add relevant code! I have fixed that, and have added the code to the post. As you can see, I use uint64_t, so I'm using an appropriate data type

[iansjack]

1. Are you sure that you are in Long Mode? Does gdb show 64-bit registers when you do "info registers"?

2. What do you mean by "it doesn't show up when I look at my pages". How are you "looking" at your pages? What does the qemu monitor show when you do "info mem"?

[Je06]

1. Are you sure that you are in Long Mode? Does gdb show 64-bit registers when you do "info registers"?

2. What do you mean by "it doesn't show up when I look at my pages". How are you "looking" at your pages? What does the qemu monitor show when you do "info mem"?

As I said, I'm using bochs. Bochs tells me that I'm in Long mode and shows Long mode registers. I'm looking at my page table in the page table output provided by bochs.

[MichaelPetch]

It is a limitation in BOCHS. It just doesn't show mappings above 4gb unless you patch the source. We have touched on this issue previously: viewtopic.php?f=1&t=27650

[Je06]

It is a limitation in BOCHS. It just doesn't show mappings above 4gb unless you patch the source. We have touched on this issue previously: viewtopic.php?f=1&t=27650

Thanks. I guest that's my issue