The BFD linker generates runtime relocations for z_input_len and z_output_len, even though they are absolute symbols.
This is fixed for binutils-2.35 [1]. Work around this for earlier versions by defining two variables input_len and output_len in addition to the symbols, and use them via position-independent references. This eliminates the last two runtime relocations in the head code and allows us to drop the -z noreloc-overflow flag to the linker. [1] https://sourceware.org/bugzilla/show_bug.cgi?id=25754 Signed-off-by: Arvind Sankar <nived...@alum.mit.edu> Reviewed-by: Ard Biesheuvel <a...@kernel.org> Reviewed-by: Fangrui Song <mask...@google.com> --- arch/x86/boot/compressed/Makefile | 8 -------- arch/x86/boot/compressed/head_32.S | 17 ++++++++--------- arch/x86/boot/compressed/head_64.S | 4 ++-- arch/x86/boot/compressed/mkpiggy.c | 6 ++++++ 4 files changed, 16 insertions(+), 19 deletions(-) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index b01c8aed0f23..242b291037e8 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -51,15 +51,7 @@ UBSAN_SANITIZE :=n KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE) # Compressed kernel should be built as PIE since it may be loaded at any # address by the bootloader. -ifeq ($(CONFIG_X86_32),y) KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker) -else -# To build 64-bit compressed kernel as PIE, we disable relocation -# overflow check to avoid relocation overflow error with a new linker -# command-line option, -z noreloc-overflow. -KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \ - && echo "-z noreloc-overflow -pie --no-dynamic-linker") -endif LDFLAGS_vmlinux := -T hostprogs := mkpiggy diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S index 8c1a4f5610f5..659fad53ca82 100644 --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -178,18 +178,17 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) /* * Do the extraction, and jump to the new kernel.. */ - /* push arguments for extract_kernel: */ - pushl $z_output_len /* decompressed length, end of relocs */ + /* push arguments for extract_kernel: */ - pushl %ebp /* output address */ - - pushl $z_input_len /* input_len */ + pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */ + pushl %ebp /* output address */ + pushl input_len@GOTOFF(%ebx) /* input_len */ leal input_data@GOTOFF(%ebx), %eax - pushl %eax /* input_data */ + pushl %eax /* input_data */ leal boot_heap@GOTOFF(%ebx), %eax - pushl %eax /* heap area */ - pushl %esi /* real mode pointer */ - call extract_kernel /* returns kernel location in %eax */ + pushl %eax /* heap area */ + pushl %esi /* real mode pointer */ + call extract_kernel /* returns kernel location in %eax */ addl $24, %esp /* diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 11429092c224..9e46729cf162 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -534,9 +534,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) movq %rsi, %rdi /* real mode address */ leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ leaq input_data(%rip), %rdx /* input_data */ - movl $z_input_len, %ecx /* input_len */ + movl input_len(%rip), %ecx /* input_len */ movq %rbp, %r8 /* output target address */ - movl $z_output_len, %r9d /* decompressed length, end of relocs */ + movl output_len(%rip), %r9d /* decompressed length, end of relocs */ call extract_kernel /* returns kernel location in %rax */ popq %rsi diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c index 7e01248765b2..52aa56cdbacc 100644 --- a/arch/x86/boot/compressed/mkpiggy.c +++ b/arch/x86/boot/compressed/mkpiggy.c @@ -60,6 +60,12 @@ int main(int argc, char *argv[]) printf(".incbin \"%s\"\n", argv[1]); printf("input_data_end:\n"); + printf(".section \".rodata\",\"a\",@progbits\n"); + printf(".globl input_len\n"); + printf("input_len:\n\t.long %lu\n", ilen); + printf(".globl output_len\n"); + printf("output_len:\n\t.long %lu\n", (unsigned long)olen); + retval = 0; bail: if (f) -- 2.26.2
