kern: Add initial ELF loader sources

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 252 insertions, 0 deletions

diff --git a/src/sys/include/os/elfload.h b/src/sys/include/os/elfload.h
new file mode 100644
index 0000000..9a64aa8
--- /dev/null
+++ b/src/sys/include/os/elfload.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _OS_ELFLOAD_H_
+#define _OS_ELFLOAD_H_
+
+#include <sys/types.h>
+
+struct proc;
+
+/*
+ * Represents a loaded ELF in memory
+ *
+ * @entrypoint: ELF entry address
+ */
+struct loaded_elf {
+    uintptr_t entrypoint;
+};
+
+int elf_load(const char *path, struct proc *proc, struct loaded_elf *res);
+
+#endif  /* !_OS_ELFLOAD_H_ */
diff --git a/src/sys/os/os_elf64.c b/src/sys/os/os_elf64.c
new file mode 100644
index 0000000..8f95f9c
--- /dev/null
+++ b/src/sys/os/os_elf64.c
@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <sys/elf.h>
+#include <sys/syslog.h>
+#include <sys/errno.h>
+#include <os/omar.h>
+#include <os/elfload.h>
+#include <vm/vm.h>
+#include <vm/mmu.h>
+#include <vm/map.h>
+#include <vm/physseg.h>
+#include <string.h>
+
+#if defined(__x86_64__)
+#define _EM_MACH  EM_X86_64
+#else
+#error "ELF loader not ported to platform"
+#endif  /* __x86_64__ */
+
+/*
+ * Verify an ELF64 using its header
+ *
+ * @eh: ELF64 header
+ *
+ * Returns zero on success, otherwise a less than
+ * zero value on error or invalid binary.
+ */
+static int
+elf64_verify(Elf64_Ehdr *eh)
+{
+    int error;
+
+    if (eh == NULL) {
+        return -EINVAL;
+    }
+
+    /* The magic must match */
+    error = memcmp(&eh->e_ident[EI_MAG0], ELFMAG, SELFMAG);
+    if (error != 0) {
+        printf("elf64_verify: bad ELF magic\n");
+        return -ENOEXEC;
+    }
+
+    /* Must be for this platform */
+    if (eh->e_machine != _EM_MACH) {
+        printf("elf64_verify: bad target machine\n");
+        return -ENOEXEC;
+    }
+
+    /* Version must be valid */
+    if (eh->e_ident[EI_VERSION] != EV_CURRENT) {
+        printf("elf64_verify: bad version\n");
+        return -ENOEXEC;
+    }
+
+    return 0;
+}
+
+/*
+ * Do the actual ELF64 loading
+ *
+ * @eh: ELF header to load
+ * @p: Process to load program as
+ *
+ * Returns zero on success, otherwise a less
+ * than zero value on failure.
+ *
+ * XXX: We'll need to handler unloading here
+ */
+static int
+elf64_do_load(Elf64_Ehdr *eh, struct proc *proc)
+{
+    static const size_t PSIZE = DEFAULT_PAGESIZE;
+    struct md_pcb *pcbp;
+    struct mmu_map spec;
+    Elf64_Phdr *phdr, *phdr_base;
+    paddr_t frame;
+    size_t npges, len, misalign;
+    uintptr_t tmp;
+    int error, prot;
+
+    if (eh == NULL || proc == NULL) {
+        return -EINVAL;
+    }
+
+    pcbp = &proc->pcb;
+#define PHDR_I(PHDR_BASE, INDEX) \
+    PTR_OFFSET(PHDR_BASE, eh->e_phentsize*(INDEX))
+    phdr_base = PTR_OFFSET(eh, eh->e_phoff);
+    for (int i = 0; i < eh->e_phnum; ++i) {
+        prot = 0;
+        phdr = PHDR_I(phdr_base, i);
+
+        /* Don't cover blank segments */
+        if (phdr->p_memsz == 0) {
+            continue;
+        }
+
+        /* What segment type is this? */
+        switch (phdr->p_type) {
+        case PT_LOAD:
+            if (ISSET(phdr->p_flags, PF_R))
+                prot |= PROT_READ;
+            if (ISSET(phdr->p_flags, PF_W))
+                prot |= PROT_WRITE;
+            if (ISSET(phdr->p_flags, PF_X))
+                prot |= PROT_EXEC;
+
+            /* Re-align the length */
+            misalign = phdr->p_memsz & (PSIZE - 1);
+            len = phdr->p_memsz;
+            len = ALIGN_UP(len + misalign, PSIZE);
+
+            frame = vm_alloc_frame(1);
+            if (frame == 0) {
+                printf("elf64_do_load: could not alloc frame\n");
+                return -ENOMEM;
+            }
+
+            /* Copy the segment data */
+            tmp = (uintptr_t)PTR_OFFSET(eh, phdr->p_offset);
+            memset(PHYS_TO_VIRT(frame), tmp, phdr->p_memsz);
+
+            /* Map the segment */
+            spec.va = phdr->p_vaddr;
+            spec.pa = frame;
+            error = vm_map(
+                &pcbp->vas,
+                &spec,
+                phdr->p_memsz,
+                prot
+            );
+
+            if (error < 0) {
+                printf("elf64_do_load: failed to map segment\n");
+                return error;
+            }
+        }
+    }
+
+    return 0;
+}
+
+/*
+ * Load an ELF binary
+ */
+int
+elf_load(const char *path, struct proc *proc, struct loaded_elf *res)
+{
+    Elf64_Ehdr *eh;
+    int error;
+    ssize_t len;
+    char *data;
+
+    if (path == NULL || proc == NULL) {
+        return -EINVAL;
+    }
+
+    if (res == NULL) {
+        return -EINVAL;
+    }
+
+    len = initrd_open(path, &data);
+    if (len < 0) {
+        printf("elf_load: failed to open \"%s\"\n", path);
+        return len;
+    }
+
+    eh = (Elf64_Ehdr *)data;
+    if ((error = elf64_verify(eh)) != 0) {
+        return error;
+    }
+
+    res->entrypoint = eh->e_entry;
+    return 0;
+}