user.c for loading userspace elfs into memoryuser

4 files changed, 158 insertions, 0 deletions

diff --git a/kernel/include/comus/limits.h b/kernel/include/comus/limits.h
index 675df47..cadfc93 100644
--- a/kernel/include/comus/limits.h
+++ b/kernel/include/comus/limits.h
@@ -22,6 +22,9 @@
 #define N_FILE_NAME 256
 #define N_DISKS 8
 
+/// elf limits
+#define N_ELF_SEGMENTS 16
+
 /// length of terminal buffer
 #define TERM_MAX_WIDTH 1920
 #define TERM_MAX_HEIGHT 1080
diff --git a/kernel/include/comus/procs.h b/kernel/include/comus/procs.h
index d92bc5d..d105867 100644
--- a/kernel/include/comus/procs.h
+++ b/kernel/include/comus/procs.h
@@ -13,6 +13,7 @@
 #include <comus/limits.h>
 #include <comus/memory.h>
 #include <lib.h>
+#include <elf.h>
 
 #define PCB_REG(pcb, x) ((pcb)->regs->x)
 #define PCB_RET(pcb) ((pcb)->regs->rax)
@@ -56,6 +57,11 @@ struct pcb {
 	size_t priority;
 	size_t ticks;
 
+	// elf metadata
+	Elf64_Ehdr elf_header;
+	Elf64_Phdr elf_segments[N_ELF_SEGMENTS];
+	Elf64_Half n_elf_segments;
+
 	// queue linkage
 	struct pcb *next; // next PDB in queue
 
diff --git a/kernel/include/comus/user.h b/kernel/include/comus/user.h
new file mode 100644
index 0000000..29c978c
--- /dev/null
+++ b/kernel/include/comus/user.h
@@ -0,0 +1,25 @@
+/**
+ * @file user.h
+ *
+ * @author Freya Murphy <freya@freyacat.org>
+ *
+ * Userland functions
+ */
+
+#ifndef USER_H_
+#define USER_H_
+
+#include <comus/procs.h>
+#include <comus/fs.h>
+
+/**
+ * Load a user elf program from a file into a pcb
+ */
+int user_load(struct pcb *pcb, struct disk *disk);
+
+/**
+ * Clean up all loaded userland data from a pcb
+ */
+void user_cleanup(struct pcb *pcb);
+
+#endif /* user.h */
diff --git a/kernel/user.c b/kernel/user.c
index 0a237e9..592b35b 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -1,5 +1,129 @@
+#include "lib/kio.h"
+#include <comus/fs.h>
 #include <comus/procs.h>
 #include <comus/memory.h>
+#include <comus/user.h>
+#include <elf.h>
+
+/// FIXME: the following code is using direct
+/// disk access instead of file access, this is
+/// because filesystems are not yet implemented.
+/// This MUST be changed once we have files.
+/// - Freya
+
+#define USER_STACK_TOP 0x800000000000
+#define USER_STACK_LEN (4 * PAGE_SIZE)
+
+static int user_load_segment(struct pcb *pcb, struct disk *disk, int idx)
+{
+	uint8_t buf[PAGE_SIZE];
+	Elf64_Phdr hdr;
+	size_t npages;
+	int ret = 0;
+
+	hdr = pcb->elf_segments[idx];
+	npages = (hdr.p_filesz + PAGE_SIZE - 1) / PAGE_SIZE;
+
+	// allocate memory in user process
+	if (mem_alloc_pages_at(pcb->memctx, npages, (void *)hdr.p_vaddr,
+						   F_WRITEABLE | F_UNPRIVILEGED) == NULL)
+		return 1;
+
+	// load data
+	for (size_t i = 0; i < npages; i++) {
+		mem_ctx_switch(kernel_mem_ctx); // disk_read is kernel internal
+		ret = disk_read(disk, hdr.p_offset + i * PAGE_SIZE, PAGE_SIZE, buf);
+		if (ret < 0)
+			break;
+		mem_ctx_switch(pcb->memctx);
+		memcpy((char *)hdr.p_vaddr + i * PAGE_SIZE, buf, PAGE_SIZE);
+	}
+
+	mem_ctx_switch(kernel_mem_ctx);
+	return ret;
+}
+
+static int user_load_segments(struct pcb *pcb, struct disk *disk)
+{
+	int ret = 0;
+
+	for (int i = 0; i < pcb->n_elf_segments; i++)
+		if ((ret = user_load_segment(pcb, disk, i)))
+			return ret;
+	return 0;
+}
+
+static int user_load_elf(struct pcb *pcb, struct disk *disk)
+{
+	int ret = 0;
+
+	ret = disk_read(disk, 0, sizeof(Elf64_Ehdr), &pcb->elf_header);
+	if (ret < 0)
+		return 1;
+
+	if (pcb->elf_header.e_phnum > N_ELF_SEGMENTS)
+		return 1;
+
+	pcb->n_elf_segments = pcb->elf_header.e_phnum;
+	ret = disk_read(disk, pcb->elf_header.e_phoff,
+					sizeof(Elf64_Phdr) * pcb->elf_header.e_phnum,
+					&pcb->elf_segments);
+	if (ret < 0)
+		return 1;
+
+	return 0;
+}
+
+static int user_setup_stack(struct pcb *pcb)
+{
+	// allocate stack
+	if (mem_alloc_pages_at(pcb->memctx, USER_STACK_LEN / PAGE_SIZE,
+						   (void *)(USER_STACK_TOP - USER_STACK_LEN),
+						   F_WRITEABLE | F_UNPRIVILEGED) == NULL)
+		return 1;
+
+	// setup initial context save area
+	pcb->regs = (struct cpu_regs *)(USER_STACK_TOP - sizeof(struct cpu_regs));
+	mem_ctx_switch(pcb->memctx);
+	memset(pcb->regs, 0, sizeof(struct cpu_regs));
+	pcb->regs->rip = pcb->elf_header.e_entry;
+	pcb->regs->cs = 0x18 | 3;
+	pcb->regs->rflags = (1 << 9);
+	pcb->regs->rsp = USER_STACK_TOP;
+	pcb->regs->ss = 0x20 | 3;
+	mem_ctx_switch(kernel_mem_ctx);
+
+	return 0;
+}
+
+int user_load(struct pcb *pcb, struct disk *disk)
+{
+	pcb->regs = NULL;
+
+	// allocate memory context
+	pcb->memctx = mem_ctx_alloc();
+	if (pcb->memctx == NULL)
+		goto fail;
+
+	// load elf information
+	if (user_load_elf(pcb, disk))
+		goto fail;
+
+	// load segments into memory
+	if (user_load_segments(pcb, disk))
+		goto fail;
+
+	// setup process stack
+	if (user_setup_stack(pcb))
+		goto fail;
+
+	// success
+	return 0;
+
+fail:
+	user_cleanup(pcb);
+	return 1;
+}
 
 void user_cleanup(struct pcb *pcb)
 {