On Tue, Apr 21, 2009 at 02:33:24PM -0700, David Daney wrote:
> This is a preliminary patch to add a vdso to all user processes.
...
> diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
> new file mode 100644
> index 0000000..a1f38a6
...
> +static void __init install_trampoline(u32 *tramp, unsigned int sigreturn)
> +{
> + tramp[0] = 0x24020000 + sigreturn; /* li v0, sigreturn */
> + tramp[1] = 0x0000000c; /* syscall */
> +}
We can do away with magic constants by building on asm/inst.h:
static void __init install_trampoline(union mips_instruction *tramp,
short sigreturn)
{
static struct i_format li_sigreturn = { /* li, v0, sigreturn */
.opcode = addiu_op,
.rs = 0, /* zero */
.rt = 2, /* v0 */
};
static struct r_format syscall = { /* syscall */
.opcode = spec_op,
.func = syscall_op
};
tramp[0].i_format = li_sigreturn;
tramp[0].i_format.simmediate = sigreturn;
tramp[1].r_format = syscall;
}
Admittedly, this isn't really a proper use of the r_format structure. The
right way is to add another structure to asm/inst.h and use that:
#ifdef __MIPSEB__
...
struct syscall_format {
unsigned int opcode : 6;
unsigned int code : 20;
unsigned int func : 6;
};
...
#else
...
struct syscall_format {
unsigned int func : 6;
unsigned int code : 20;
unsigned int opcode : 6;
};
...
#endif
Then we could do the syscall the right way by using syscall_format
instead of r_format...
...
> +int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> +{
> + int ret;
> + unsigned long addr;
> + struct mm_struct *mm = current->mm;
> +
> + down_write(&mm->mmap_sem);
> +
> + addr = vdso_addr(mm->start_stack);
> +
> + addr = get_unmapped_area(NULL, addr, PAGE_SIZE, 0, 0);
> + if (IS_ERR_VALUE(addr)) {
> + ret = addr;
> + goto up_fail;
> + }
> +
> + ret = install_special_mapping(mm, addr, PAGE_SIZE,
> + VM_READ|VM_EXEC|
> + VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
> + VM_ALWAYSDUMP,
> + &vdso_page);
> +
> + if (ret)
> + goto up_fail;
> +
> + mm->context.vdso = (void *)addr;
> +
> +up_fail:
It seems that this is an unexpected condition that probably indicates
a failure of the expected state of the process at this point. Perhaps
a pr_err() or pr_warning() would be appropriate?
> + up_write(&mm->mmap_sem);
> + return ret;
> +}
