b8e85e6f - objtool/x86: Separate arch-specific and generic parts

Mon, 11 Mar 2024 14:23:47 +0000

objtool/x86: Separate arch-specific and generic partsMove init_orc_entry(), write_orc_entry(), reg_name(), orc_type_name()and print_reg() from generic orc_gen.c and orc_dump.c to arch-specificorc.c, then introduce a new function orc_print_dump() to print info.This is preparation for later patch, no functionality change.Co-developed-by: Jinyang He Signed-off-by: Jinyang He Co-developed-by: Youling Tang Signed-off-by: Youling Tang Signed-off-by: Tiezhu Yang Signed-off-by: Huacai Chen List of files: /linux-6.15/tools/objtool/arch/x86/Build

eda3dc90 - objtool: Abstract alternative special case handling

Fri, 04 Sep 2020 15:30:22 +0000

objtool: Abstract alternative special case handlingSome alternatives associated with a specific feature need to be treatedin a special way. Since the features and how to treat them vary from onearchitecture to another, move the special case handling to arch specificcode.Reviewed-by: Miroslav Benes Signed-off-by: Julien Thierry Signed-off-by: Josh Poimboeuf List of files: /linux-6.15/tools/objtool/arch/x86/Build

d046b725 - objtool: Move x86 insn decoder to a common location

Thu, 29 Aug 2019 22:41:18 +0000

objtool: Move x86 insn decoder to a common locationThe kernel tree has three identical copies of the x86 instructiondecoder. Two of them are in the tools subdir.The tools subdir is supposed to be completely standalone and separatefrom the kernel. So having at least one copy of the kernel decoder inthe tools subdir is unavoidable. However, we don't need *two* of them.Move objtool's copy of the decoder to a shared location, so that perfwill also be able to use it.Signed-off-by: Josh Poimboeuf Reviewed-by: Masami Hiramatsu Acked-by: Peter Zijlstra (Intel) Cc: Adrian Hunter Cc: Jiri Olsa Cc: x86@kernel.orgLink: http://lore.kernel.org/lkml/55b486b88f6bcd0c9a2a04b34f964860c8390ca8.1567118001.git.jpoimboe@redhat.comSigned-off-by: Arnaldo Carvalho de Melo List of files: /linux-6.15/tools/objtool/arch/x86/Build

6a77cff8 - objtool: Move synced files to their original relative locations

Mon, 06 Nov 2017 13:21:50 +0000

objtool: Move synced files to their original relative locationsThis will enable more straightforward comparisons, and it also makes thefiles 100% identical.Suggested-by: Ingo Molnar Signed-off-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/407b2aaa317741f48fcf821592c0e96ab3be1890.1509974346.git.jpoimboe@redhat.comSigned-off-by: Ingo Molnar List of files: /linux-6.15/tools/objtool/arch/x86/Build

442f04c3 - objtool: Add tool to perform compile-time stack metadata validation

Mon, 29 Feb 2016 04:22:41 +0000

objtool: Add tool to perform compile-time stack metadata validationThis adds a host tool named objtool which has a "check" subcommand whichanalyzes .o files to ensure the validity of stack metadata. It enforcesa set of rules on asm code and C inline assembly code so that stacktraces can be reliable.For each function, it recursively follows all possible code paths andvalidates the correct frame pointer state at each instruction.It also follows code paths involving kernel special sections, like.altinstructions, __jump_table, and __ex_table, which can addalternative execution paths to a given instruction (or set ofinstructions). Similarly, it knows how to follow switch statements, forwhich gcc sometimes uses jump tables.Here are some of the benefits of validating stack metadata:a) More reliable stack traces for frame pointer enabled kernels Frame pointers are used for debugging purposes. They allow runtime code and debug tools to be able to walk the stack to determine the chain of function call sites that led to the currently executing code. For some architectures, frame pointers are enabled by CONFIG_FRAME_POINTER. For some other architectures they may be required by the ABI (sometimes referred to as "backchain pointers"). For C code, gcc automatically generates instructions for setting up frame pointers when the -fno-omit-frame-pointer option is used. But for asm code, the frame setup instructions have to be written by hand, which most people don't do. So the end result is that CONFIG_FRAME_POINTER is honored for C code but not for most asm code. For stack traces based on frame pointers to be reliable, all functions which call other functions must first create a stack frame and update the frame pointer. If a first function doesn't properly create a stack frame before calling a second function, the *caller* of the first function will be skipped on the stack trace. For example, consider the following example backtrace with frame pointers enabled: [] dump_stack+0x4b/0x63 [] cmdline_proc_show+0x12/0x30 [] seq_read+0x108/0x3e0 [] proc_reg_read+0x42/0x70 [] __vfs_read+0x37/0x100 [] vfs_read+0x86/0x130 [] SyS_read+0x58/0xd0 [] entry_SYSCALL_64_fastpath+0x12/0x76 It correctly shows that the caller of cmdline_proc_show() is seq_read(). If we remove the frame pointer logic from cmdline_proc_show() by replacing the frame pointer related instructions with nops, here's what it looks like instead: [] dump_stack+0x4b/0x63 [] cmdline_proc_show+0x12/0x30 [] proc_reg_read+0x42/0x70 [] __vfs_read+0x37/0x100 [] vfs_read+0x86/0x130 [] SyS_read+0x58/0xd0 [] entry_SYSCALL_64_fastpath+0x12/0x76 Notice that cmdline_proc_show()'s caller, seq_read(), has been skipped. Instead the stack trace seems to show that cmdline_proc_show() was called by proc_reg_read(). The benefit of "objtool check" here is that because it ensures that *all* functions honor CONFIG_FRAME_POINTER, no functions will ever[*] be skipped on a stack trace. [*] unless an interrupt or exception has occurred at the very beginning of a function before the stack frame has been created, or at the very end of the function after the stack frame has been destroyed. This is an inherent limitation of frame pointers.b) 100% reliable stack traces for DWARF enabled kernels This is not yet implemented. For more details about what is planned, see tools/objtool/Documentation/stack-validation.txt.c) Higher live patching compatibility rate This is not yet implemented. For more details about what is planned, see tools/objtool/Documentation/stack-validation.txt.To achieve the validation, "objtool check" enforces the following rules:1. Each callable function must be annotated as such with the ELF function type. In asm code, this is typically done using the ENTRY/ENDPROC macros. If objtool finds a return instruction outside of a function, it flags an error since that usually indicates callable code which should be annotated accordingly. This rule is needed so that objtool can properly identify each callable function in order to analyze its stack metadata.2. Conversely, each section of code which is *not* callable should *not* be annotated as an ELF function. The ENDPROC macro shouldn't be used in this case. This rule is needed so that objtool can ignore non-callable code. Such code doesn't have to follow any of the other rules.3. Each callable function which calls another function must have the correct frame pointer logic, if required by CONFIG_FRAME_POINTER or the architecture's back chain rules. This can by done in asm code with the FRAME_BEGIN/FRAME_END macros. This rule ensures that frame pointer based stack traces will work as designed. If function A doesn't create a stack frame before calling function B, the _caller_ of function A will be skipped on the stack trace.4. Dynamic jumps and jumps to undefined symbols are only allowed if: a) the jump is part of a switch statement; or b) the jump matches sibling call semantics and the frame pointer has the same value it had on function entry. This rule is needed so that objtool can reliably analyze all of a function's code paths. If a function jumps to code in another file, and it's not a sibling call, objtool has no way to follow the jump because it only analyzes a single file at a time.5. A callable function may not execute kernel entry/exit instructions. The only code which needs such instructions is kernel entry code, which shouldn't be be in callable functions anyway. This rule is just a sanity check to ensure that callable functions return normally.It currently only supports x86_64. I tried to make the code generic sothat support for other architectures can hopefully be plugged inrelatively easily.On my Lenovo laptop with a i7-4810MQ 4-core/8-thread CPU, building thekernel with objtool checking every .o file adds about three seconds oftotal build time. It hasn't been optimized for performance yet, sothere are probably some opportunities for better build performance.Signed-off-by: Josh Poimboeuf Cc: Andrew Morton Cc: Andy Lutomirski Cc: Arnaldo Carvalho de Melo Cc: Bernd Petrovitsch Cc: Borislav Petkov Cc: Chris J Arges Cc: Jiri Slaby Cc: Linus Torvalds Cc: Michal Marek Cc: Namhyung Kim Cc: Pedro Alves Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: live-patching@vger.kernel.orgLink: http://lkml.kernel.org/r/f3efb173de43bd067b060de73f856567c0fa1174.1456719558.git.jpoimboe@redhat.comSigned-off-by: Ingo Molnar List of files: /linux-6.15/tools/objtool/arch/x86/Build

Changes in Build

b8e85e6f - objtool/x86: Separate arch-specific and generic parts

eda3dc90 - objtool: Abstract alternative special case handling

d046b725 - objtool: Move x86 insn decoder to a common location

6a77cff8 - objtool: Move synced files to their original relative locations

442f04c3 - objtool: Add tool to perform compile-time stack metadata validation