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Better default guest_base 

Avoid loading linux-user applications in address space already used/reserved
by the host.

Signed-off-by: Paul Brook <paul@codesourcery.com>
This commit is contained in:
Paul Brook 2010-05-05 16:32:59 +01:00
parent 2e9a5713f0
commit c581deda32
1 changed files with 68 additions and 7 deletions
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75
linux-user/elfload.c
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@ -1666,19 +1666,80 @@ int load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
*/
if (!have_guest_base) {
/*
* Go through ELF program header table and find out whether
* any of the segments drop below our current mmap_min_addr and
* in that case set guest_base to corresponding address.
*/
* Go through ELF program header table and find the address
* range used by loadable segments. Check that this is available on
* the host, and if not find a suitable value for guest_base. */
abi_ulong app_start = ~0;
abi_ulong app_end = 0;
abi_ulong addr;
unsigned long host_start;
unsigned long real_start;
unsigned long host_size;
for (i = 0, elf_ppnt = elf_phdata; i < elf_ex.e_phnum;
i++, elf_ppnt++) {
if (elf_ppnt->p_type != PT_LOAD)
continue;
if (HOST_PAGE_ALIGN(elf_ppnt->p_vaddr) < mmap_min_addr) {
guest_base = HOST_PAGE_ALIGN(mmap_min_addr);
break;
addr = elf_ppnt->p_vaddr;
if (addr < app_start) {
app_start = addr;
}
addr += elf_ppnt->p_memsz;
if (addr > app_end) {
app_end = addr;
}
}
/* If we don't have any loadable segments then something
is very wrong. */
assert(app_start < app_end);
/* Round addresses to page boundaries. */
app_start = app_start & qemu_host_page_mask;
app_end = HOST_PAGE_ALIGN(app_end);
if (app_start < mmap_min_addr) {
host_start = HOST_PAGE_ALIGN(mmap_min_addr);
} else {
host_start = app_start;
if (host_start != app_start) {
fprintf(stderr, "qemu: Address overflow loading ELF binary\n");
abort();
}
}
host_size = app_end - app_start;
while (1) {
/* Do not use mmap_find_vma here because that is limited to the
guest address space. We are going to make the
guest address space fit whatever we're given. */
real_start = (unsigned long)mmap((void *)host_start, host_size,
PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0);
if (real_start == (unsigned long)-1) {
fprintf(stderr, "qemu: Virtual memory exausted\n");
abort();
}
if (real_start == host_start) {
break;
}
/* That address didn't work. Unmap and try a different one.
The address the host picked because is typically
right at the top of the host address space and leaves the
guest with no usable address space. Resort to a linear search.
We already compensated for mmap_min_addr, so this should not
happen often. Probably means we got unlucky and host address
space randomization put a shared library somewhere
inconvenient. */
munmap((void *)real_start, host_size);
host_start += qemu_host_page_size;
if (host_start == app_start) {
/* Theoretically possible if host doesn't have any
suitably aligned areas. Normally the first mmap will
fail. */
fprintf(stderr, "qemu: Unable to find space for application\n");
abort();
}
}
qemu_log("Relocating guest address space from 0x" TARGET_ABI_FMT_lx
" to 0x%lx\n", app_start, real_start);
guest_base = real_start - app_start;
}
#endif /* CONFIG_USE_GUEST_BASE */