kernel: exec_elf64: Ensure '.bss' is zero filledmain

Implement logic to go through the section header table and explicitly
zero fill all entries of type SHT_NOBITS

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

2 files changed, 99 insertions, 0 deletions

diff --git a/sys/include/sys/elf.h b/sys/include/sys/elf.h
index af5f6d6..76c6d43 100644
--- a/sys/include/sys/elf.h
+++ b/sys/include/sys/elf.h
@@ -496,4 +496,70 @@ typedef struct {
   Elf64_Xword sh_entsize;	/* Entry size if section holds table */
 } Elf64_Shdr;
 
+/* Special section indices.  */
+
+#define SHN_UNDEF	0		/* Undefined section */
+#define SHN_LORESERVE	0xff00		/* Start of reserved indices */
+#define SHN_LOPROC	0xff00		/* Start of processor-specific */
+#define SHN_BEFORE	0xff00		/* Order section before all others
+					   (Solaris).  */
+#define SHN_AFTER	0xff01		/* Order section after all others
+					   (Solaris).  */
+#define SHN_HIPROC	0xff1f		/* End of processor-specific */
+#define SHN_LOOS	0xff20		/* Start of OS-specific */
+#define SHN_HIOS	0xff3f		/* End of OS-specific */
+#define SHN_ABS		0xfff1		/* Associated symbol is absolute */
+#define SHN_COMMON	0xfff2		/* Associated symbol is common */
+#define SHN_XINDEX	0xffff		/* Index is in extra table.  */
+#define SHN_HIRESERVE	0xffff		/* End of reserved indices */
+
+/* Legal values for sh_type (section type).  */
+
+#define SHT_NULL	  0		/* Section header table entry unused */
+#define SHT_PROGBITS	  1		/* Program data */
+#define SHT_SYMTAB	  2		/* Symbol table */
+#define SHT_STRTAB	  3		/* String table */
+#define SHT_RELA	  4		/* Relocation entries with addends */
+#define SHT_HASH	  5		/* Symbol hash table */
+#define SHT_DYNAMIC	  6		/* Dynamic linking information */
+#define SHT_NOTE	  7		/* Notes */
+#define SHT_NOBITS	  8		/* Program space with no data (bss) */
+#define SHT_REL		  9		/* Relocation entries, no addends */
+#define SHT_SHLIB	  10		/* Reserved */
+#define SHT_DYNSYM	  11		/* Dynamic linker symbol table */
+#define SHT_INIT_ARRAY	  14		/* Array of constructors */
+#define SHT_FINI_ARRAY	  15		/* Array of destructors */
+#define SHT_PREINIT_ARRAY 16		/* Array of pre-constructors */
+#define SHT_GROUP	  17		/* Section group */
+#define SHT_SYMTAB_SHNDX  18		/* Extended section indeces */
+#define	SHT_NUM		  19		/* Number of defined types.  */
+#define SHT_LOOS	  0x60000000	/* Start OS-specific.  */
+#define SHT_CHECKSUM	  0x6ffffff8	/* Checksum for DSO content.  */
+#define SHT_LOSUNW	  0x6ffffffa	/* Sun-specific low bound.  */
+#define SHT_SUNW_move	  0x6ffffffa
+#define SHT_SUNW_COMDAT   0x6ffffffb
+#define SHT_SUNW_syminfo  0x6ffffffc
+#define SHT_HISUNW	  0x6fffffff	/* Sun-specific high bound.  */
+#define SHT_HIOS	  0x6fffffff	/* End OS-specific type */
+#define SHT_LOPROC	  0x70000000	/* Start of processor-specific */
+#define SHT_HIPROC	  0x7fffffff	/* End of processor-specific */
+#define SHT_LOUSER	  0x80000000	/* Start of application-specific */
+#define SHT_HIUSER	  0x8fffffff	/* End of application-specific */
+
+/* Legal values for sh_flags (section flags).  */
+
+#define SHF_WRITE	     (1 << 0)	/* Writable */
+#define SHF_ALLOC	     (1 << 1)	/* Occupies memory during execution */
+#define SHF_EXECINSTR	     (1 << 2)	/* Executable */
+#define SHF_MERGE	     (1 << 4)	/* Might be merged */
+#define SHF_STRINGS	     (1 << 5)	/* Contains nul-terminated strings */
+#define SHF_INFO_LINK	     (1 << 6)	/* `sh_info' contains SHT index */
+#define SHF_LINK_ORDER	     (1 << 7)	/* Preserve order after combining */
+#define SHF_OS_NONCONFORMING (1 << 8)	/* Non-standard OS specific handling
+					   required */
+#define SHF_GROUP	     (1 << 9)	/* Section is member of a group.  */
+#define SHF_TLS		     (1 << 10)	/* Section hold thread-local data.  */
+#define SHF_COMPRESSED	     (1 << 11)	/* Section with compressed data. */
+#define SHF_MASKOS	     0x0ff00000	/* OS-specific.  */
+#define SHF_MASKPROC	     0xf0000000	/* Processor-specific */
 #endif      /* _SYS_ELF_H_ */
diff --git a/sys/kern/exec_elf64.c b/sys/kern/exec_elf64.c
index 987dda4..9706e77 100644
--- a/sys/kern/exec_elf64.c
+++ b/sys/kern/exec_elf64.c
@@ -49,11 +49,43 @@
 #define PHDR(HDRP, IDX) \
     (void *)((uintptr_t)HDRP + (HDRP)->e_phoff + (HDRP->e_phentsize * IDX))
 
+#define SHDR(HDRP, IDX) \
+    (void *)((uintptr_t)HDRP + (HDRP)->e_shoff + (HDRP->e_shentsize * IDX))
+
 struct elf_file {
     char *data;
     size_t size;
 };
 
+static int
+elf_parse_shdrs(Elf64_Ehdr *eh)
+{
+    Elf64_Shdr *shp;
+    uint32_t nshdr;
+
+    if (eh == NULL) {
+        return -EINVAL;
+    }
+
+    nshdr = eh->e_shnum;
+    for (uint32_t i = 0; i < nshdr; ++i) {
+        shp = SHDR(eh, i);
+
+        /* Drop null entries */
+        if (shp->sh_type == SHT_NULL) {
+            continue;
+        }
+
+        switch (shp->sh_type) {
+        case SHT_NOBITS:
+            memset((void *)shp->sh_addr, 0x0, shp->sh_size);
+            break;
+        }
+    }
+
+    return 0;
+}
+
 /*
  * Load the file and give back an "elf_file"
  * structure.
@@ -243,6 +275,7 @@ elf64_load(const char *pathname, struct proc *td, struct exec_prog *prog)
         }
     }
 
+    elf_parse_shdrs(hdr);
     memcpy(prog->loadmap, loadmap, sizeof(loadmap));
     prog->start = start;
     prog->end = end;