On Tue, Aug 04, 2015 at 01:53:24PM +1000, David Gibson wrote:
> 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 <drjones@xxxxxxxxxx>
> > ---
> > 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.
Thanks, I'll change it.
drew
>
> > +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 <drjones@xxxxxxxxxx>
> > + *
> > + * 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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