On Mon, Aug 03, 2015 at 04:41:27PM +0200, Andrew Jones wrote: > QEMU loads the unit test, but due to the way it translates the > unit test's linker VMA to the LMA, we can't just link such that > VMA == LMA. Thus, we link with VMA == 0x0, and then deal with > relocation. > > Signed-off-by: Andrew Jones <[email protected]> > --- > configure | 2 ++ > powerpc/Makefile.common | 13 +++++++++--- > powerpc/Makefile.ppc64 | 1 + > powerpc/cstart64.S | 40 +++++++++++++++++++++++++++++++---- > powerpc/flat.lds | 13 +++++++++++- > powerpc/reloc64.c | 55 > +++++++++++++++++++++++++++++++++++++++++++++++++ > 6 files changed, 116 insertions(+), 8 deletions(-) > create mode 100644 powerpc/reloc64.c > > diff --git a/configure b/configure > index b367224093369..b2ad199da7873 100755 > --- a/configure > +++ b/configure > @@ -5,6 +5,7 @@ kerneldir=/lib/modules/$(uname -r)/build > cc=gcc > ld=ld > objcopy=objcopy > +objdump=objdump > ar=ar > arch=`uname -m | sed -e s/i.86/i386/ | sed -e 's/arm.*/arm/'` > host=$arch > @@ -132,6 +133,7 @@ PROCESSOR=$processor > CC=$cross_prefix$cc > LD=$cross_prefix$ld > OBJCOPY=$cross_prefix$objcopy > +OBJDUMP=$cross_prefix$objdump > AR=$cross_prefix$ar > API=$api > TEST_DIR=$testdir > diff --git a/powerpc/Makefile.common b/powerpc/Makefile.common > index d6356540918a5..b130342dee60e 100644 > --- a/powerpc/Makefile.common > +++ b/powerpc/Makefile.common > @@ -27,6 +27,7 @@ CFLAGS += -Wextra > CFLAGS += -O2 > CFLAGS += -I lib -I lib/libfdt > CFLAGS += -Wa,-mregnames > +CFLAGS += -fpie > > asm-offsets = lib/$(ARCH)/asm-offsets.h > include scripts/asm-offsets.mak > @@ -43,11 +44,17 @@ libgcc := $(shell $(CC) $(machine) > --print-libgcc-file-name) > start_addr := $(shell printf "%x\n" $$(( $(phys_base) + $(kernel_offset) ))) > > FLATLIBS = $(libcflat) $(LIBFDT_archive) $(libgcc) > -%.elf: LDFLAGS = $(CFLAGS) -nostdlib > +%.elf: LDFLAGS = $(CFLAGS) -nostdlib -pie > %.elf: %.o $(FLATLIBS) powerpc/flat.lds > $(CC) $(LDFLAGS) -o $@ \ > -Wl,-T,powerpc/flat.lds,--build-id=none,-Ttext=$(start_addr) \ > $(filter %.o, $^) $(FLATLIBS) > + @echo -n Checking $@ for unsupported reloc types... > + @if $(OBJDUMP) -R $@ | grep R_ | grep -v R_PPC64_RELATIVE; then \ > + false; \ > + else \ > + echo " looks good."; \ > + fi > > powerpc_clean: libfdt_clean asm_offsets_clean > $(RM) $(TEST_DIR)/*.{o,elf} \ > @@ -59,5 +66,5 @@ generated_files = $(asm-offsets) > > test_cases: $(generated_files) $(tests-common) $(tests) > > -$(TEST_DIR)/$(TEST).elf: $(cstart.o) $(TEST_DIR)/$(TEST).o > -$(TEST_DIR)/selftest.elf: $(cstart.o) $(TEST_DIR)/selftest.o > +$(TEST_DIR)/$(TEST).elf: $(cstart.o) $(reloc.o) $(TEST_DIR)/$(TEST).o > +$(TEST_DIR)/selftest.elf: $(cstart.o) $(reloc.o) $(TEST_DIR)/selftest.o > diff --git a/powerpc/Makefile.ppc64 b/powerpc/Makefile.ppc64 > index 7c61933dfa8ba..7274e0d98b5a5 100644 > --- a/powerpc/Makefile.ppc64 > +++ b/powerpc/Makefile.ppc64 > @@ -8,6 +8,7 @@ ldarch = elf64-powerpc #elf64-powerpcle (eventually) > kernel_offset = 0x0 > > cstart.o = $(TEST_DIR)/cstart64.o > +reloc.o = $(TEST_DIR)/reloc64.o > cflatobjs += lib/ppc64/processor.o > cflatobjs += lib/ppc64/spinlock.o > > diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S > index 141d4563563d5..8edaaa6e251fc 100644 > --- a/powerpc/cstart64.S > +++ b/powerpc/cstart64.S > @@ -26,18 +26,50 @@ > */ > .globl start > start: > - LOAD_REG_IMMEDIATE(r1, stackptr) > - LOAD_REG_IMMEDIATE(r2, tocptr) > + /* > + * We were loaded at QEMU's kernel load address, but we're not > + * allowed to link there due to how QEMU deals with linker VMAs, > + * so we just linked at zero. This means the first thing to do is > + * to find our stack and toc, and then do a relocate. > + */ > + bl . + 4
"bl 0f" might make the connection to the following instructions
clearer.
> +0: mflr r31
> + subi r31, r31, 0b - start /* QEMU's kernel load address */
> + ld r1, (p_stack - start)(r31)
> + ld r2, (p_toc - start)(r31)
> + add r1, r1, r31
> + add r2, r2, r31
> +
> + /* save DTB pointer */
> + std r3, 56(r1)
> +
> + /*
> + * Call relocate. relocate is C code, but careful to not use
> + * any global references, as they may use absolute addresses,
> + * which are, obviously, not yet relocated.
> + */
> + mr r3, r31
> + ld r4, (p_dyn - start)(r31)
> + add r4, r4, r31
> + bl .relocate
> +
> + /* complete setup */
> + ld r3, 56(r1)
> bl .setup
>
> /* run the test */
> - LOAD_REG_IMMEDIATE(r5, __argc)
> - LOAD_REG_IMMEDIATE(r4, __argv)
> + LOAD_REG_ADDR(r5, __argc)
> + LOAD_REG_ADDR(r4, __argv)
> lwz r3, 0(r5)
> bl .main
> bl .exit
> b halt
>
> +.align 3
> +p_stack: .llong stackptr
> +p_toc: .llong tocptr
> +p_dyn: .llong dynamic_start
> +
> .text
> .align 3
>
> diff --git a/powerpc/flat.lds b/powerpc/flat.lds
> index bd075efb2c51b..8a573d27346de 100644
> --- a/powerpc/flat.lds
> +++ b/powerpc/flat.lds
> @@ -6,11 +6,22 @@ SECTIONS
> etext = .;
> .opd : { *(.opd) }
> . = ALIGN(16);
> + .dynamic : {
> + dynamic_start = .;
> + *(.dynamic)
> + }
> + .dynsym : {
> + dynsym_start = .;
> + *(.dynsym)
> + }
> + .rela.dyn : { *(.rela*) }
> + . = ALIGN(16);
> .data : {
> *(.data)
> + *(.data.rel*)
> }
> . = ALIGN(16);
> - .rodata : { *(.rodata) }
> + .rodata : { *(.rodata) *(.rodata.*) }
> . = ALIGN(16);
> .bss : { *(.bss) }
> . = ALIGN(16);
> diff --git a/powerpc/reloc64.c b/powerpc/reloc64.c
> new file mode 100644
> index 0000000000000..2804823bdfee3
> --- /dev/null
> +++ b/powerpc/reloc64.c
> @@ -0,0 +1,55 @@
> +/*
> + * relocate R_PPC_RELATIVE RELA entries. Normally this is done in
> + * assembly code to avoid the risk of using absolute addresses before
> + * they're relocated. We use C, but cautiously (no global references).
> + *
> + * Copyright (C) 2015, Red Hat Inc, Andrew Jones <[email protected]>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.
> + */
> +#define DT_NULL 0
> +#define DT_RELA 7
> +#define DT_RELACOUNT 0x6ffffff9
> +#define R_PPC_RELATIVE 22
> +
> +struct elf64_dyn {
> + signed long long tag;
> + unsigned long long val;
> +};
> +
> +#define RELA_GET_TYPE(rela_ptr) ((rela_ptr)->info & 0xffffffff)
> +struct elf64_rela {
> + unsigned long long offset;
> + unsigned long long info;
> + signed long long addend;
> +};
> +
> +void relocate(unsigned long load_addr, struct elf64_dyn *dyn_table)
> +{
> + unsigned long long rela_addr = 0, rela_count = 0, *addr;
> + struct elf64_dyn *d = dyn_table;
> + struct elf64_rela *r;
> +
> + while (d && d->tag != DT_NULL) {
> + if (d->tag == DT_RELA)
> + rela_addr = d->val;
> + else if (d->tag == DT_RELACOUNT)
> + rela_count = d->val;
> + if (rela_addr && rela_count)
> + break;
> + ++d;
> + }
> +
> + if (!rela_addr || !rela_count)
> + return;
> +
> + r = (void *)(rela_addr + load_addr);
> +
> + while (rela_count--) {
> + if (RELA_GET_TYPE(r) == R_PPC_RELATIVE) {
> + addr = (void *)(r->offset + load_addr);
> + *addr = r->addend + load_addr;
> + }
> + ++r;
> + }
> +}
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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