linux-toradex.git/tools/objtool/Documentation, branch v5.11-rc3

objtool: Add support for intra-function calls

2020-04-30T18:14:33+00:00

Change objtool to support intra-function calls. On x86, an intra-function
call is represented in objtool as a push onto the stack (of the return
address), and a jump to the destination address. That way the stack
information is correctly updated and the call flow is still accurate.

Signed-off-by: Alexandre Chartre 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Miroslav Benes 
Acked-by: Josh Poimboeuf 
Link: https://lkml.kernel.org/r/20200414103618.12657-4-alexandre.chartre@oracle.com

objtool: Fix ORC vs alternatives

2020-04-30T18:14:31+00:00

Jann reported that (for instance) entry_64.o:general_protection has
very odd ORC data:

  0000000000000f40 :
  #######sp:sp+8 bp:(und) type:iret end:0
    f40:       90                      nop
  #######sp:(und) bp:(und) type:call end:0
    f41:       90                      nop
    f42:       90                      nop
  #######sp:sp+8 bp:(und) type:iret end:0
    f43:       e8 a8 01 00 00          callq  10f0 
  #######sp:sp+0 bp:(und) type:regs end:0
    f48:       f6 84 24 88 00 00 00    testb  $0x3,0x88(%rsp)
    f4f:       03
    f50:       74 00                   je     f52 
    f52:       48 89 e7                mov    %rsp,%rdi
    f55:       48 8b 74 24 78          mov    0x78(%rsp),%rsi
    f5a:       48 c7 44 24 78 ff ff    movq   $0xffffffffffffffff,0x78(%rsp)
    f61:       ff ff
    f63:       e8 00 00 00 00          callq  f68 
    f68:       e9 73 02 00 00          jmpq   11e0 
  #######sp:(und) bp:(und) type:call end:0
    f6d:       0f 1f 00                nopl   (%rax)

Note the entry at 0xf41. Josh found this was the result of commit:

  764eef4b109a ("objtool: Rewrite alt->skip_orig")

Due to the early return in validate_branch() we no longer set
insn->cfi of the original instruction stream (the NOPs at 0xf41 and
0xf42) and we'll end up with the above weirdness.

In other discussions we realized alternatives should be ORC invariant;
that is, due to there being only a single ORC table, it must be valid
for all alternatives. The easiest way to ensure this is to not allow
any stack modifications in alternatives.

When we enforce this latter observation, we get the property that the
whole alternative must have the same CFI, which we can employ to fix
the former report.

Fixes: 764eef4b109a ("objtool: Rewrite alt->skip_orig")
Reported-by: Jann Horn 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Miroslav Benes 
Acked-by: Josh Poimboeuf 
Link: https://lkml.kernel.org/r/20200428191659.499074346@infradead.org

objtool: Documentation: document UACCESS warnings

2020-04-22T08:53:49+00:00

Compiling with Clang and CONFIG_KASAN=y was exposing a few warnings:

  call to memset() with UACCESS enabled

Document how to fix these for future travelers.

Link: https://github.com/ClangBuiltLinux/linux/issues/876
Suggested-by: Kamalesh Babulal 
Suggested-by: Matt Helsley 
Suggested-by: Peter Zijlstra 
Suggested-by: Randy Dunlap 
Signed-off-by: Nick Desaulniers 
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Ingo Molnar

docs: fix broken documentation links

2019-06-08T19:42:13+00:00

Mostly due to x86 and acpi conversion, several documentation
links are still pointing to the old file. Fix them.

Signed-off-by: Mauro Carvalho Chehab 
Reviewed-by: Wolfram Sang 
Reviewed-by: Sven Van Asbroeck 
Reviewed-by: Bhupesh Sharma 
Acked-by: Mark Brown 
Signed-off-by: Jonathan Corbet

Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2019-05-16T17:29:00+00:00

Pull core fixes from Ingo Molnar:
 "A handful of objtool updates, plus a documentation addition for
  __ab_c_size()"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  objtool: Fix whitelist documentation typo
  objtool: Fix function fallthrough detection
  objtool: Don't use ignore flag for fake jumps
  overflow.h: Add comment documenting __ab_c_size()

objtool: Fix whitelist documentation typo

2019-05-15T05:57:50+00:00

The directive specified in the documentation to add an exception
for a single file in a Makefile was inverted.

Signed-off-by: Raphael Gault 
Signed-off-by: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/522362a1b934ee39d0af0abb231f68e160ecf1a8.1557874043.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar

docs: livepatch: convert docs to ReST and rename to *.rst

2019-05-07T22:05:49+00:00

Convert livepatch documentation to ReST format. The changes
are mostly trivial, as the documents are already on a good
shape. Just a few markup changes are needed for Sphinx to
properly parse the docs.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - The in-file TOC becomes a comment, in order to skip it from the
    output, as Sphinx already generates an index there.
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab 
Signed-off-by: Petr Mladek 
Acked-by: Miroslav Benes 
Acked-by: Josh Poimboeuf 
Acked-by: Joe Lawrence 
Reviewed-by: Kamalesh Babulal 
Signed-off-by: Jonathan Corbet

x86/asm: Fix inline asm call constraints for Clang

2017-09-23T13:06:20+00:00

For inline asm statements which have a CALL instruction, we list the
stack pointer as a constraint to convince GCC to ensure the frame
pointer is set up first:

  static inline void foo()
  {
	register void *__sp asm(_ASM_SP);
	asm("call bar" : "+r" (__sp))
  }

Unfortunately, that pattern causes Clang to corrupt the stack pointer.

The fix is easy: convert the stack pointer register variable to a global
variable.

It should be noted that the end result is different based on the GCC
version.  With GCC 6.4, this patch has exactly the same result as
before:

	defconfig	defconfig-nofp	distro		distro-nofp
 before	9820389		9491555		8816046		8516940
 after	9820389		9491555		8816046		8516940

With GCC 7.2, however, GCC's behavior has changed.  It now changes its
behavior based on the conversion of the register variable to a global.
That somehow convinces it to *always* set up the frame pointer before
inserting *any* inline asm.  (Therefore, listing the variable as an
output constraint is a no-op and is no longer necessary.)  It's a bit
overkill, but the performance impact should be negligible.  And in fact,
there's a nice improvement with frame pointers disabled:

	defconfig	defconfig-nofp	distro		distro-nofp
 before	9796316		9468236		9076191		8790305
 after	9796957		9464267		9076381		8785949

So in summary, while listing the stack pointer as an output constraint
is no longer necessary for newer versions of GCC, it's still needed for
older versions.

Suggested-by: Andrey Ryabinin 
Reported-by: Matthias Kaehlcke 
Signed-off-by: Josh Poimboeuf 
Cc: Alexander Potapenko 
Cc: Andy Lutomirski 
Cc: Arnd Bergmann 
Cc: Dmitriy Vyukov 
Cc: Linus Torvalds 
Cc: Miguel Bernal Marin 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/3db862e970c432ae823cf515c52b54fec8270e0e.1505942196.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar

objtool: Add ORC unwind table generation

2017-07-18T08:57:43+00:00

Now that objtool knows the states of all registers on the stack for each
instruction, it's straightforward to generate debuginfo for an unwinder
to use.

Instead of generating DWARF, generate a new format called ORC, which is
more suitable for an in-kernel unwinder.  See
Documentation/x86/orc-unwinder.txt for a more detailed description of
this new debuginfo format and why it's preferable to DWARF.

Signed-off-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Jiri Slaby 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/c9b9f01ba6c5ed2bdc9bb0957b78167fdbf9632e.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar

objtool: Implement stack validation 2.0

2017-06-30T08:19:19+00:00

This is a major rewrite of objtool.  Instead of only tracking frame
pointer changes, it now tracks all stack-related operations, including
all register saves/restores.

In addition to making stack validation more robust, this also paves the
way for undwarf generation.

Signed-off-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Jiri Slaby 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/678bd94c0566c6129bcc376cddb259c4c5633004.1498659915.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar