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Re: [Xen-devel] [PATCH v2 07/13] xsplice: Add helper elf routines (v2)



On 01/14/2016 09:47 PM, Konrad Rzeszutek Wilk wrote:
From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Add Elf routines and data structures in preparation for loading an
xSplice payload.

We also add an macro that will print where we failed during
the ELF parsing.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
v2: - With the #define ELFSIZE in the ARM file we can use the common
      #defines instead of using #ifdef CONFIG_ARM_32.
     - Add checks for ELF file.
     - Add name to be printed.
     - Add len for easier ELF checks.
     - Expand on the checks. Add macro.
---
diff --git a/xen/common/xsplice_elf.c b/xen/common/xsplice_elf.c
new file mode 100644
index 0000000..a5e9d63
--- /dev/null
+++ b/xen/common/xsplice_elf.c
@@ -0,0 +1,201 @@
+#include <xen/lib.h>
+#include <xen/errno.h>
+#include <xen/xsplice.h>
+#include <xen/xsplice_elf.h>
+
+#define return_(x) { printk(XENLOG_DEBUG "%s:%d rc: %d\n",  \
+                            __func__,__LINE__, x); return x; }
+
+struct xsplice_elf_sec *xsplice_elf_sec_by_name(const struct xsplice_elf *elf,
+                                                const char *name)
+{
+    unsigned int i;
+
+    for ( i = 0; i < elf->hdr->e_shnum; i++ )
+    {
+        if ( !strcmp(name, elf->sec[i].name) )
+            return &elf->sec[i];
+    }
+
+    return NULL;
+}
+
+static int elf_resolve_sections(struct xsplice_elf *elf, uint8_t *data)
+{
+    struct xsplice_elf_sec *sec;
+    unsigned int i;
+
+    sec = xmalloc_array(struct xsplice_elf_sec, elf->hdr->e_shnum);
+    if ( !sec )
+    {
+        printk(XENLOG_ERR "Could not allocate memory for section table!\n");

Shouldn't this printk be removed if you're using return_?

+        return_(-ENOMEM);
+    }
+
+    /* N.B. We also will ingest SHN_UNDEF sections. */
+    for ( i = 0; i < elf->hdr->e_shnum; i++ )
+    {
+        ssize_t delta = elf->hdr->e_shoff + i * elf->hdr->e_shentsize;
+
+        if ( delta + sizeof(Elf_Shdr) > elf->len )
+            return_(-EINVAL);
+
+        sec[i].sec = (Elf_Shdr *)(data + delta);
+        delta = sec[i].sec->sh_offset;
+
+        if ( delta > elf->len )
+            return_(-EINVAL);
+
+        sec[i].data = data + delta;
+        /* Name is populated in xsplice_elf_sections_name. */
+        sec[i].name = NULL;
+
+        if ( sec[i].sec->sh_type == SHT_SYMTAB )
+        {
+                if ( elf->symtab )
+                    return_(-EINVAL);
+                elf->symtab = &sec[i];
+                /* elf->symtab->sec->sh_link would point to the right section
+                 * but we hadn't finished parsing all the sections. */
+                if ( elf->symtab->sec->sh_link > elf->hdr->e_shnum )
+                    return_(-EINVAL);
+        }
+    }
+    elf->sec = sec;
+    if ( !elf->symtab )
+        return_(-EINVAL);
+
+    /* There can be multiple SHT_STRTAB so pick the right one. */
+    elf->strtab = &sec[elf->symtab->sec->sh_link];
+
+    if ( elf->symtab->sec->sh_size == 0 || elf->symtab->sec->sh_entsize == 0 )
+        return_(-EINVAL);
+
+    if ( elf->symtab->sec->sh_entsize != sizeof(Elf_Sym) )
+        return_(-EINVAL);
+
+    return 0;
+}
+
snip
+
+static int elf_get_sym(struct xsplice_elf *elf, uint8_t *data)
+{
+    struct xsplice_elf_sec *symtab_sec, *strtab_sec;
+    struct xsplice_elf_sym *sym;
+    unsigned int i, delta, offset;
+
+    symtab_sec = elf->symtab;
+
+    strtab_sec = elf->strtab;
+
+    /* Pointers arithmetic to get file offset. */
+    offset = strtab_sec->data - data;
+
+    ASSERT( offset == strtab_sec->sec->sh_offset );
+    /* symtab_sec->data was computed in elf_resolve_sections. */
+    ASSERT((symtab_sec->sec->sh_offset + data) == symtab_sec->data );
+
+    /* No need to check values as elf_resolve_sections did it. */
+    elf->nsym = symtab_sec->sec->sh_size / symtab_sec->sec->sh_entsize;
+
+    sym = xmalloc_array(struct xsplice_elf_sym, elf->nsym);
+    if ( !sym )
+    {
+        printk(XENLOG_ERR "%s: Could not allocate memory for symbols\n", 
elf->name);

Shouldn't this printk be removed if you're using return_?

--
Ross Lagerwall

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