lkml.org 
[lkml]   [2020]   [Jun]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[RFC][PATCH 3/3] objtool: Fix noinstr vs KCOV
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) <peterz@infradead.org>
---
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.
*

\
 
 \ /
  Last update: 2020-06-12 16:38    [W:0.119 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site