On Tue, 2012-11-27 at 14:39 +1100, Anton Blanchard wrote:
> The ppc64 kernel can get loaded at any address which means
> our very early init code in prom_init.c must be relocatable. We do
> this with a pretty nasty RELOC() macro that we wrap accesses of
> variables with. It is very fragile and sometimes we forget to add a
> RELOC() to an uncommon path or sometimes a compiler change breaks it.
>
> 32bit has a much more elegant solution where we build prom_init.c
> with -mrelocatable and then process the relocations manually.
> Unfortunately we can't do the equivalent on 64bit and we would
> have to build the entire kernel relocatable (-pie), resulting in a
> large increase in kernel footprint (megabytes of relocation data).
> The relocation data will be marked __initdata but it still creates
> more pressure on our already tight memory layout at boot.
>
> Alan Modra pointed out that the 64bit ABI is relocatable even
> if we don't build with -pie, we just need to relocate the TOC.
> This patch implements that idea and relocates the TOC entries of
> prom_init.c. An added bonus is there are very few relocations to
> process which helps keep boot times on simulators down.
>
> gcc does not put 64bit integer constants into the TOC but to be
> safe we may want a build time script which passes through the
> prom_init.c TOC entries to make sure everything looks reasonable.
My only potential objection was that it might have been cleaner to
actually build prom_init.c as a separate binary alltogether and piggy
back it...
Ben.
> Signed-off-by: Anton Blanchard <an...@samba.org>
> ---
>
> To keep the patch small and reviewable, I separated the removal
> of the RELOC macro into a follow up patch.
>
> For simplicity I do the relocation in C but if self brain surgery
> keeps people up at night we can move it into assembly.
>
> Index: b/arch/powerpc/kernel/prom_init.c
> ===================================================================
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -66,8 +66,8 @@
> * is running at whatever address it has been loaded at.
> * On ppc32 we compile with -mrelocatable, which means that references
> * to extern and static variables get relocated automatically.
> - * On ppc64 we have to relocate the references explicitly with
> - * RELOC. (Note that strings count as static variables.)
> + * ppc64 objects are always relocatable, we just need to relocate the
> + * TOC.
> *
> * Because OF may have mapped I/O devices into the area starting at
> * KERNELBASE, particularly on CHRP machines, we can't safely call
> @@ -79,13 +79,12 @@
> * On ppc64, 64 bit values are truncated to 32 bits (and
> * fortunately don't get interpreted as two arguments).
> */
> +#define RELOC(x) (x)
> +#define ADDR(x) (u32)(unsigned long)(x)
> +
> #ifdef CONFIG_PPC64
> -#define RELOC(x) (*PTRRELOC(&(x)))
> -#define ADDR(x) (u32) add_reloc_offset((unsigned long)(x))
> #define OF_WORKAROUNDS 0
> #else
> -#define RELOC(x) (x)
> -#define ADDR(x) (u32) (x)
> #define OF_WORKAROUNDS of_workarounds
> int of_workarounds;
> #endif
> @@ -334,9 +333,6 @@ static void __init prom_printf(const cha
> struct prom_t *_prom = &RELOC(prom);
>
> va_start(args, format);
> -#ifdef CONFIG_PPC64
> - format = PTRRELOC(format);
> -#endif
> for (p = format; *p != 0; p = q) {
> for (q = p; *q != 0 && *q != '\n' && *q != '%'; ++q)
> ;
> @@ -437,9 +433,6 @@ static unsigned int __init prom_claim(un
>
> static void __init __attribute__((noreturn)) prom_panic(const char *reason)
> {
> -#ifdef CONFIG_PPC64
> - reason = PTRRELOC(reason);
> -#endif
> prom_print(reason);
> /* Do not call exit because it clears the screen on pmac
> * it also causes some sort of double-fault on early pmacs */
> @@ -929,7 +922,7 @@ static void __init prom_send_capabilitie
> * (we assume this is the same for all cores) and use it to
> * divide NR_CPUS.
> */
> - cores = (u32
> *)PTRRELOC(&ibm_architecture_vec[IBM_ARCH_VEC_NRCORES_OFFSET]);
> + cores = (u32
> *)&ibm_architecture_vec[IBM_ARCH_VEC_NRCORES_OFFSET];
> if (*cores != NR_CPUS) {
> prom_printf("WARNING ! "
> "ibm_architecture_vec structure
> inconsistent: %lu!\n",
> @@ -2850,6 +2843,53 @@ static void __init prom_check_initrd(uns
> #endif /* CONFIG_BLK_DEV_INITRD */
> }
>
> +#ifdef CONFIG_PPC64
> +#ifdef CONFIG_RELOCATABLE
> +static void reloc_toc(void)
> +{
> +}
> +
> +static void unreloc_toc(void)
> +{
> +}
> +#else
> +static void __reloc_toc(void *tocstart, unsigned long offset,
> + unsigned long nr_entries)
> +{
> + unsigned long i;
> + unsigned long *toc_entry = (unsigned long *)tocstart;
> +
> + for (i = 0; i < nr_entries; i++) {
> + *toc_entry = *toc_entry + offset;
> + toc_entry++;
> + }
> +}
> +
> +static void reloc_toc(void)
> +{
> + unsigned long offset = reloc_offset();
> + unsigned long nr_entries =
> + (__prom_init_toc_end - __prom_init_toc_start) / sizeof(long);
> +
> + /* Need to add offset to get at __prom_init_toc_start */
> + __reloc_toc(__prom_init_toc_start + offset, offset, nr_entries);
> +
> + mb();
> +}
> +
> +static void unreloc_toc(void)
> +{
> + unsigned long offset = reloc_offset();
> + unsigned long nr_entries =
> + (__prom_init_toc_end - __prom_init_toc_start) / sizeof(long);
> +
> + mb();
> +
> + /* __prom_init_toc_start has been relocated, no need to add offset */
> + __reloc_toc(__prom_init_toc_start, -offset, nr_entries);
> +}
> +#endif
> +#endif
>
> /*
> * We enter here early on, when the Open Firmware prom is still
> @@ -2867,6 +2907,8 @@ unsigned long __init prom_init(unsigned
> #ifdef CONFIG_PPC32
> unsigned long offset = reloc_offset();
> reloc_got2(offset);
> +#else
> + reloc_toc();
> #endif
>
> _prom = &RELOC(prom);
> @@ -3061,6 +3103,8 @@ unsigned long __init prom_init(unsigned
>
> #ifdef CONFIG_PPC32
> reloc_got2(-offset);
> +#else
> + unreloc_toc();
> #endif
>
> #ifdef CONFIG_PPC_EARLY_DEBUG_OPAL
> Index: b/arch/powerpc/kernel/prom_init_check.sh
> ===================================================================
> --- a/arch/powerpc/kernel/prom_init_check.sh
> +++ b/arch/powerpc/kernel/prom_init_check.sh
> @@ -22,7 +22,7 @@ __secondary_hold_acknowledge __secondary
> strcmp strcpy strlcpy strlen strncmp strstr logo_linux_clut224
> reloc_got2 kernstart_addr memstart_addr linux_banner _stext
> opal_query_takeover opal_do_takeover opal_enter_rtas opal_secondary_entry
> -boot_command_line"
> +boot_command_line __prom_init_toc_start __prom_init_toc_end"
>
> NM="$1"
> OBJ="$2"
> Index: b/arch/powerpc/kernel/vmlinux.lds.S
> ===================================================================
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -218,6 +218,11 @@ SECTIONS
>
> .got : AT(ADDR(.got) - LOAD_OFFSET) {
> __toc_start = .;
> +#ifndef CONFIG_RELOCATABLE
> + __prom_init_toc_start = .;
> + arch/powerpc/kernel/prom_init.o*(.toc .got)
> + __prom_init_toc_end = .;
> +#endif
> *(.got)
> *(.toc)
> }
> Index: b/arch/powerpc/Makefile
> ===================================================================
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -136,6 +136,7 @@ head-$(CONFIG_FSL_BOOKE) := arch/powerpc
> head-$(CONFIG_PPC64) += arch/powerpc/kernel/entry_64.o
> head-$(CONFIG_PPC_FPU) += arch/powerpc/kernel/fpu.o
> head-$(CONFIG_ALTIVEC) += arch/powerpc/kernel/vector.o
> +head-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE) += arch/powerpc/kernel/prom_init.o
>
> core-y += arch/powerpc/kernel/ \
> arch/powerpc/mm/ \
> Index: b/arch/powerpc/kernel/Makefile
> ===================================================================
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -91,7 +91,6 @@ obj-$(CONFIG_RELOCATABLE_PPC32) += reloc
> obj-$(CONFIG_PPC32) += entry_32.o setup_32.o
> obj-$(CONFIG_PPC64) += dma-iommu.o iommu.o
> obj-$(CONFIG_KGDB) += kgdb.o
> -obj-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE) += prom_init.o
> obj-$(CONFIG_MODULES) += ppc_ksyms.o
> obj-$(CONFIG_BOOTX_TEXT) += btext.o
> obj-$(CONFIG_SMP) += smp.o
> @@ -142,6 +141,7 @@ GCOV_PROFILE_kprobes.o := n
> extra-$(CONFIG_PPC_FPU) += fpu.o
> extra-$(CONFIG_ALTIVEC) += vector.o
> extra-$(CONFIG_PPC64) += entry_64.o
> +extra-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE) += prom_init.o
>
> extra-y += systbl_chk.i
> $(obj)/systbl.o: systbl_chk
> Index: b/arch/powerpc/include/asm/sections.h
> ===================================================================
> --- a/arch/powerpc/include/asm/sections.h
> +++ b/arch/powerpc/include/asm/sections.h
> @@ -10,6 +10,9 @@
>
> extern char __end_interrupts[];
>
> +extern char __prom_init_toc_start[];
> +extern char __prom_init_toc_end[];
> +
> static inline int in_kernel_text(unsigned long addr)
> {
> if (addr >= (unsigned long)_stext && addr < (unsigned long)__init_end)
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