On Fri, 16 Jan 2015, Markos Chandras wrote:
> diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c
> index c92b15df6893..2ac33d2375ca 100644
> --- a/arch/mips/kernel/elf.c
> +++ b/arch/mips/kernel/elf.c
> @@ -11,29 +11,102 @@
> #include <linux/elf.h>
> #include <linux/sched.h>
>
> +/* FPU modes */
> enum {
> - FP_ERROR = -1,
> - FP_DOUBLE_64A = -2,
> + FP_FRE,
> + FP_FR0,
> + FP_FR1,
> };
>
> +/**
> + * struct mode_req - ABI FPU mode requirements
> + * @single: The program being loaded needs an FPU but it will only issue
> + * single precision instructions meaning that it can execute in
> + * either FR0 or FR1.
> + * @soft: The soft(-float) requirement means that the program being
> + * loaded needs has no FPU dependency at all (i.e. it has no
> + * FPU instructions).
> + * @fr1: The program being loaded depends on FPU being in FR=1 mode.
> + * @frdefault: The program being loaded depends on the default FPU mode.
> + * That is FR0 for O32 and FR1 for N32/N64.
> + * @fre: The program being loaded depends on FPU with FRE=1. This mode is
> + * a bridge which uses FR=1 whilst still being able to maintain
> + * full compatibility with pre-existing code using the O32 FP32
> + * ABI.
> + *
> + * More information about the FP ABIs can be found here:
> + *
> + * https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
> + *
> + */
> +
> +struct mode_req {
> + bool single;
> + bool soft;
> + bool fr1;
> + bool frdefault;
> + bool fre;
> +};
> +
> +static const struct mode_req fpu_reqs[] = {
> + [MIPS_ABI_FP_ANY] = { true, true, true, true, true },
> + [MIPS_ABI_FP_DOUBLE] = { false, false, false, true, true },
> + [MIPS_ABI_FP_SINGLE] = { true, false, false, false, false },
> + [MIPS_ABI_FP_SOFT] = { false, true, false, false, false },
> + [MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
> + [MIPS_ABI_FP_XX] = { false, false, true, true, true },
> + [MIPS_ABI_FP_64] = { false, false, true, false, false },
> + [MIPS_ABI_FP_64A] = { false, false, true, false, true }
> +};
> +
> +/*
> + * Mode requirements when .MIPS.abiflags is not present in the ELF.
> + * Not present means that everything is acceptable except FR1.
> + */
> +static struct mode_req none_req = { true, true, false, true, true };
> +
> int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
> bool is_interp, struct arch_elf_state *state)
> {
> - struct elfhdr *ehdr = _ehdr;
> - struct elf_phdr *phdr = _phdr;
> + struct elf32_hdr *ehdr32 = _ehdr;
> + struct elf32_phdr *phdr32 = _phdr;
> + struct elf64_phdr *phdr64 = _phdr;
Minor nit, I won't be picking on it if you have a strong feeling against,
but I think it would be slightly cleaner if you had used unions here -- no
risk of people picking bad habits that would hurt if any of these
structures were written, causing aliasing issues.
So e.g.:
union {
struct elf32_hdr e32;
struct elf64_hdr e64;
} *ehdr = _ehdr;
union {
struct elf32_phdr p32;
struct elf64_phdr p64;
} *phdr = _phdr;
and then:
> + /* Lets see if this is an O32 ELF */
> + if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
> + /* FR = 1 for N32 */
> + if (ehdr32->e_flags & EF_MIPS_ABI2)
> + state->overall_fp_mode = FP_FR1;
> + else
> + /* Set a good default FPU mode for O32*/
> + state->overall_fp_mode = cpu_has_mips_r6 ?
> + FP_FRE : FP_FR0;
> +
> + if (phdr32->p_type != PT_MIPS_ABIFLAGS)
> + return 0;
> +
> + if (phdr32->p_filesz < sizeof(abiflags))
> + return -EINVAL;
> +
> + ret = kernel_read(elf, phdr32->p_offset,
> + (char *)&abiflags,
> + sizeof(abiflags));
/* Lets see if this is an O32 ELF */
if (ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32) {
/* FR = 1 for N32 */
if (ehdr->e32.e_flags & EF_MIPS_ABI2)
state->overall_fp_mode = FP_FR1;
else
/* Set a good default FPU mode for O32*/
state->overall_fp_mode = cpu_has_mips_r6 ?
FP_FRE : FP_FR0;
if (phdr->p32.p_type != PT_MIPS_ABIFLAGS)
return 0;
if (phdr->p32.p_filesz < sizeof(abiflags))
return -EINVAL;
ret = kernel_read(elf, phdr->p32.p_offset,
(char *)&abiflags,
sizeof(abiflags));
-- and so on... As you can see the result isn't even much different in
terms of readability or source code size, while avoiding any possible
aliasing issues.
Maciej
