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Subject[Patch 18/21] Generate the data sections for ELF Core
Generate the "data" for the memory regions. Also write down the section header 
if we have, number of phdrs > PN_XNUM.
The vma areas are read, page by page using access_process_vm() without an
mmap_sem. If there are active threads, then we may miss a vma if it is removed
while we are doing the read.

Signed-off-by: Suzuki K. Poulose <suzuki@in.ibm.com>
Signed-off-by: Ananth N. Mavinakayanahalli <ananth@in.ibm.com>
---
fs/proc/gencore-elf.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 87 insertions(+), 3 deletions(-)
Index: linux-2.6.36-rc7/fs/proc/gencore-elf.c
===================================================================
--- linux-2.6.36-rc7.orig/fs/proc/gencore-elf.c
+++ linux-2.6.36-rc7/fs/proc/gencore-elf.c
@@ -333,10 +333,29 @@ static int create_elf_header(struct core
return 0;
}

+/*
+ * Verify if the fpos asked for in read is valid.
+ * Returns the phdr corresponding to offset, else NULL.
+ */
+static struct elf_phdr *get_pos_elfphdr(struct core_proc *cp, loff_t pos)
+{
+ struct elfhdr *elf_hdr = (struct elfhdr *)cp->elf_buf;
+ struct elf_phdr *phdr = (struct elf_phdr*)(cp->elf_buf + elf_hdr->e_phoff);
+ int i;
+
+ for (i = 0; i < cp->nphdrs; i++, phdr++) {
+ unsigned long end = phdr->p_offset + phdr->p_filesz;
+ if ((pos >= phdr->p_offset) && (pos < end))
+ return phdr;
+ }
+ return NULL;
+}
+
ssize_t elf_read_gencore(struct core_proc *cp, char __user *buffer,
size_t buflen, loff_t *fpos)
{
- ssize_t ret = 0;
+ ssize_t ret = 0, acc = 0;
+ struct elfhdr *elf_hdr = (struct elfhdr *)cp->elf_buf;

if (!cp->notes_size) {
if (!collect_notes(cp)) {
@@ -367,16 +386,81 @@ ssize_t elf_read_gencore(struct core_pro
ret = -EFAULT;
goto out;
} else {
- ret = bcp;
+ acc = bcp;
*fpos += bcp;
buflen -= bcp;
buffer += bcp;
}
}

+
if (*fpos > cp->size)
- goto out;
+ goto done;
+
+ /*
+ * Read from the vma segments
+ * a. verify if the *fpos is within a phdr
+ * b. Use access_process_vm() to get data page by page
+ * c. copy_to_user into user buffer
+ */
+
+ while (buflen) {
+ size_t bufsz, offset, bytes;
+ char *readbuf;
+ struct elf_phdr *phdr = get_pos_elfphdr(cp, *fpos);
+
+ if (!phdr)
+ break;
+
+ bufsz = (buflen > PAGE_SIZE) ? PAGE_SIZE : buflen;
+ readbuf = kmalloc(bufsz, GFP_KERNEL);
+ if (!readbuf) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ offset = *fpos - phdr->p_offset;
+ bytes = access_process_vm(cp->task, (phdr->p_vaddr + offset),
+ readbuf, bufsz, 0);
+ if (!bytes) {
+ ret = -EIO;
+ goto out;
+ }
+ if (copy_to_user(buffer, readbuf, bytes)) {
+ ret = -EFAULT;
+ kfree(readbuf);
+ goto out;
+ } else
+ acc += bytes;
+
+ kfree(readbuf);
+ buflen -= bytes;
+ buffer += bytes;
+ *fpos += bytes;
+ }
+
+ /* Fill extnum section header if present */
+ if (buflen &&
+ elf_hdr->e_shoff &&
+ (*fpos >= elf_hdr->e_shoff) &&
+ (*fpos < (elf_hdr->e_shoff + sizeof(struct elf_shdr)))) {
+
+ off_t offset = *fpos - elf_hdr->e_shoff;
+ size_t shdrsz = sizeof(struct elf_shdr) - offset;
+
+ shdrsz = (buflen < shdrsz) ? buflen : shdrsz;
+ if (copy_to_user(buffer, ((char *)cp->shdr) + offset, shdrsz)) {
+ ret = -EFAULT;
+ goto out;
+ } else {
+ acc += shdrsz;
+ buflen -= shdrsz;
+ buffer += shdrsz;
+ }
+ }

+done:
+ ret = acc;
out:
return ret;
}

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