On Fri, Jun 12, 2020 at 4:37 PM Peter Zijlstra <pet...@infradead.org> wrote:
>
> Since many compilers cannot disable KCOV with a function attribute,
> help it to NOP out any __sanitizer_cov_*() calls injected in noinstr
> code.
>
> This turns:
>
> 12: e8 00 00 00 00 callq 17 <lockdep_hardirqs_on+0x17>
> 13: R_X86_64_PLT32 __sanitizer_cov_trace_pc-0x4
>
> into:
>
> 12: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> 13: R_X86_64_NONE __sanitizer_cov_trace_pc-0x4
>
> Just like recordmcount does.
>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Acked-by: Dmitry Vyukov <dvyu...@google.com>
Thanks!
> ---
> tools/objtool/arch.h | 2 ++
> tools/objtool/arch/x86/decode.c | 18 ++++++++++++++++++
> tools/objtool/arch/x86/include/arch_elf.h | 6 ++++++
> tools/objtool/check.c | 19 +++++++++++++++++++
> 4 files changed, 45 insertions(+)
>
> --- a/tools/objtool/arch.h
> +++ b/tools/objtool/arch.h
> @@ -84,4 +84,6 @@ unsigned long arch_jump_destination(stru
>
> unsigned long arch_dest_reloc_offset(int addend);
>
> +const char *arch_nop_insn(int len);
> +
> #endif /* _ARCH_H */
> --- a/tools/objtool/arch/x86/decode.c
> +++ b/tools/objtool/arch/x86/decode.c
> @@ -565,3 +565,21 @@ void arch_initial_func_cfi_state(struct
> state->regs[16].base = CFI_CFA;
> state->regs[16].offset = -8;
> }
> +
> +const char *arch_nop_insn(int len)
> +{
> + static const char nops[5][5] = {
> + /* 1 */ { 0x90 },
> + /* 2 */ { 0x66, 0x90 },
> + /* 3 */ { 0x0f, 0x1f, 0x00 },
> + /* 4 */ { 0x0f, 0x1f, 0x40, 0x00 },
> + /* 5 */ { 0x0f, 0x1f, 0x44, 0x00, 0x00 },
> + };
> +
> + if (len < 1 || len > 5) {
> + WARN("invalid NOP size: %d\n", len);
> + return NULL;
> + }
> +
> + return nops[len-1];
> +}
> --- /dev/null
> +++ b/tools/objtool/arch/x86/include/arch_elf.h
> @@ -0,0 +1,6 @@
> +#ifndef _OBJTOOL_ARCH_ELF
> +#define _OBJTOOL_ARCH_ELF
> +
> +#define R_NONE R_X86_64_NONE
> +
> +#endif /* _OBJTOOL_ARCH_ELF */
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -12,6 +12,7 @@
> #include "check.h"
> #include "special.h"
> #include "warn.h"
> +#include "arch_elf.h"
>
> #include <linux/hashtable.h>
> #include <linux/kernel.h>
> @@ -744,6 +745,24 @@ static int add_call_destinations(struct
> insn->call_dest = reloc->sym;
>
> /*
> + * Many compilers cannot disable KCOV with a function
> attribute
> + * so they need a little help, NOP out any KCOV calls from
> noinstr
> + * text.
> + */
> + if (insn->sec->noinstr &&
> + !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
> + if (reloc) {
> + reloc->type = R_NONE;
> + elf_write_reloc(file->elf, reloc);
> + }
> +
> + elf_write_insn(file->elf, insn->sec,
> + insn->offset, insn->len,
> + arch_nop_insn(insn->len));
> + insn->type = INSN_NOP;
> + }
> +
> + /*
> * Whatever stack impact regular CALLs have, should be undone
> * by the RETURN of the called function.
> *
>
>
