From 108ced98b17f5eff77de99f57cea65a3c8ddd2cb Mon Sep 17 00:00:00 2001
From: Amelia Coutard <eliottulio.coutard@gmail.com>
Date: Wed, 1 Mar 2023 14:57:54 +0100
Subject: [PATCH] Fixed elf page-alignment necessity. Now only requires no page
 overlap

---
 kernel/src/kernel.cpp | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/kernel/src/kernel.cpp b/kernel/src/kernel.cpp
index c5d8591..8c1569c 100644
--- a/kernel/src/kernel.cpp
+++ b/kernel/src/kernel.cpp
@@ -200,13 +200,12 @@ extern "C" void kmain(unsigned long magic, os::phys_ptr<const multiboot2::info_s
 			continue;
 		}
 		os::print("Segment: loadable\n");
-		os::assert((std::uintptr_t(program_header.p_vaddr) & 0xFFF) == 0, "Program segment not 4KiB aligned.");
 		os::assert(0x1000 <= std::uint64_t(program_header.p_vaddr)
 				&& std::uint64_t(program_header.p_vaddr + program_header.p_memsz) < 0x10'0000'0000,
 			"Program segments must be contained between 0x1000 and 0x10'0000'0000 (i.e. 64GiB).");
 
 		// Allocate memory for segment:
-		std::size_t nb_pages = (program_header.p_memsz + 0x1000) / 0x1000;
+		std::size_t nb_pages = (std::uint64_t(program_header.p_vaddr) % 0x1000 + program_header.p_memsz + 0x1000 - 1) / 0x1000;
 		for (std::size_t i = 0; i < nb_pages; i++) {
 			const auto indices = os::paging::calc_page_table_indices(program_header.p_vaddr + i * 0x1000);
 			if (PML4T.contents[indices.pml4e].P == 0) {
@@ -227,11 +226,10 @@ extern "C" void kmain(unsigned long magic, os::phys_ptr<const multiboot2::info_s
 				set_base_address(PDT.contents[indices.pde], os::phys_ptr<os::paging::PT>(PT_alloc.ptr.get_phys_addr()));
 			}
 			os::paging::PT& PT = *get_base_address(PDT.contents[indices.pde]);
-			if (PT.contents[indices.pe].P == 0) {
-				PT.contents[indices.pe] = {.P = 1, .R_W = (program_header.flags & 2) >> 1, .U_S = 1, .PWT = 0, .PCD = 0, .PAT = 0, .G = 0, .base_address = 0, .NX = 0};
-				const auto page_alloc = os::paging::page_allocator.allocate(1);
-				set_page_base_address(PT.contents[indices.pe], os::phys_ptr<os::paging::page>(page_alloc.ptr.get_phys_addr()));
-			}
+			os::assert(PT.contents[indices.pe].P == 0, "Process segments' memory overlaps the same pages.");
+			PT.contents[indices.pe] = {.P = 1, .R_W = (program_header.flags & 2) >> 1, .U_S = 1, .PWT = 0, .PCD = 0, .PAT = 0, .G = 0, .base_address = 0, .NX = 0};
+			const auto page_alloc = os::paging::page_allocator.allocate(1);
+			set_page_base_address(PT.contents[indices.pe], os::phys_ptr<os::paging::page>(page_alloc.ptr.get_phys_addr()));
 		}
 
 		// Initialise memory for segment:
@@ -267,11 +265,10 @@ extern "C" void kmain(unsigned long magic, os::phys_ptr<const multiboot2::info_s
 			set_base_address(PDT.contents[indices.pde], os::phys_ptr<os::paging::PT>(PT_alloc.ptr.get_phys_addr()));
 		}
 		os::paging::PT& PT = *get_base_address(PDT.contents[indices.pde]);
-		if (PT.contents[indices.pe].P == 0) {
-			PT.contents[indices.pe] = {.P = 1, .R_W = 1, .U_S = 1, .PWT = 0, .PCD = 0, .PAT = 0, .G = 0, .base_address = 0, .NX = 0};
-			const auto page_alloc = os::paging::page_allocator.allocate(1);
-			set_page_base_address(PT.contents[indices.pe], os::phys_ptr<os::paging::page>(page_alloc.ptr.get_phys_addr()));
-		}
+		os::assert(PT.contents[indices.pe].P == 0, "Process segments' memory overlaps the same pages.");
+		PT.contents[indices.pe] = {.P = 1, .R_W = 1, .U_S = 1, .PWT = 0, .PCD = 0, .PAT = 0, .G = 0, .base_address = 0, .NX = 0};
+		const auto page_alloc = os::paging::page_allocator.allocate(1);
+		set_page_base_address(PT.contents[indices.pe], os::phys_ptr<os::paging::page>(page_alloc.ptr.get_phys_addr()));
 	}
 
 	// Initialise stack to 0.
-- 
2.47.0