kernel/arch/mips/include/asm/jump_label.h, branch linux-rolling-stable

mips: Replace ASSEMBLY with ASSEMBLER in the mips headers

2025-08-29T20:34:29Z

While the GCC and Clang compilers already define __ASSEMBLER__ automatically when compiling assembler code, __ASSEMBLY__ is a macro that only gets defined by the Makefiles in the kernel. Defining such a macro was necessary in the early days of the kernel, since GCC only started providing __ASSEMBLER__ since version 3.0 in 2000 (see https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=f8f769ea4e69 ). However, having two macros can be very confusing nowadays for the developers when switching between userspace and kernelspace coding, or when dealing with uapi headers that should use __ASSEMBLER__ instead. So let's now standardize on the __ASSEMBLER__ macro that is provided by the compilers. This is almost a completely mechanical patch (done with a simple "sed -i" statement), with just one comment tweaked manually in arch/mips/include/asm/cpu.h (that was missing some underscores). Cc: Thomas Bogendoerfer Cc: linux-mips@vger.kernel.org Reviewed-by: Philippe Mathieu-Daudé Reviewed-by: Maciej W. Rozycki Signed-off-by: Thomas Huth Signed-off-by: Thomas Bogendoerfer

work around gcc bugs with 'asm goto' with outputs

2024-02-09T23:57:48Z

We've had issues with gcc and 'asm goto' before, and we created a 'asm_volatile_goto()' macro for that in the past: see commits 3f0116c3238a ("compiler/gcc4: Add quirk for 'asm goto' miscompilation bug") and a9f180345f53 ("compiler/gcc4: Make quirk for asm_volatile_goto() unconditional"). Then, much later, we ended up removing the workaround in commit 43c249ea0b1e ("compiler-gcc.h: remove ancient workaround for gcc PR 58670") because we no longer supported building the kernel with the affected gcc versions, but we left the macro uses around. Now, Sean Christopherson reports a new version of a very similar problem, which is fixed by re-applying that ancient workaround. But the problem in question is limited to only the 'asm goto with outputs' cases, so instead of re-introducing the old workaround as-is, let's rename and limit the workaround to just that much less common case. It looks like there are at least two separate issues that all hit in this area: (a) some versions of gcc don't mark the asm goto as 'volatile' when it has outputs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420 which is easy to work around by just adding the 'volatile' by hand. (b) Internal compiler errors: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422 which are worked around by adding the extra empty 'asm' as a barrier, as in the original workaround. but the problem Sean sees may be a third thing since it involves bad code generation (not an ICE) even with the manually added 'volatile'. but the same old workaround works for this case, even if this feels a bit like voodoo programming and may only be hiding the issue. Reported-and-tested-by: Sean Christopherson Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/ Cc: Nick Desaulniers Cc: Uros Bizjak Cc: Jakub Jelinek Cc: Andrew Pinski Signed-off-by: Linus Torvalds

mips: move jump_label_apply_nops() declaration to header

2023-12-11T01:21:40Z

Instead of an extern declaration in the C file with the caller, move it to an appropriate header, avoiding arch/mips/kernel/jump_label.c:93:6: error: no previous prototype for 'jump_label_apply_nops' [-Werror=missing-prototypes] Link: https://lkml.kernel.org/r/20231204115710.2247097-9-arnd@kernel.org Signed-off-by: Arnd Bergmann Cc: Stephen Rothwell Cc: Thomas Bogendoerfer Signed-off-by: Andrew Morton

jump_label: make initial NOP patching the special case

2022-06-24T07:48:55Z

Instead of defaulting to patching NOP opcodes at init time, and leaving it to the architectures to override this if this is not needed, switch to a model where doing nothing is the default. This is the common case by far, as only MIPS requires NOP patching at init time. On all other architectures, the correct encodings are emitted by the compiler and so no initial patching is needed. Signed-off-by: Ard Biesheuvel Signed-off-by: Peter Zijlstra (Intel) Acked-by: Mark Rutland Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220615154142.1574619-4-ardb@kernel.org

MIPS: jump_label: Use compact branches for >= r6

2019-04-09T23:21:30Z

MIPSr6 introduced compact branches which have no delay slots. Make use of them for jump labels in order to avoid the need for a nop to fill the branch or jump delay slot, saving 4 bytes of code for each static branch. Signed-off-by: Paul Burton Cc: linux-mips@vger.kernel.org

MIPS: jump_label: Remove redundant nops

2019-04-09T23:21:28Z

Both arch_static_branch() & arch_static_branch_jump() emit a control transfer instruction (ie. branch or jump) without disabling assembler re-ordering. As such the assembler will automatically fill their delay slots. Both functions follow their branch or jump with an explicit nop that at first appears to be there to fill the delay slot, but given that the assembler will do that the explicit nops serve no purpose & we end up with our branch or jump followed by 2 nops. Remove the redundant nops. Signed-off-by: Paul Burton Cc: linux-mips@vger.kernel.org

MIPS: Fix kernel crash for R6 in jump label branch function

2019-03-11T18:11:11Z

Insert Branch instruction instead of NOP to make sure assembler don't patch code in forbidden slot. In jump label function, it might be possible to patch Control Transfer Instructions(CTIs) into forbidden slot, which will generate Reserved Instruction exception in MIPS release 6. Signed-off-by: Archer Yan Reviewed-by: Paul Burton [paul.burton@mips.com: - Add MIPS prefix to subject. - Mark for stable from v4.0, which introduced r6 support, onwards.] Signed-off-by: Paul Burton Cc: linux-mips@vger.kernel.org Cc: stable@vger.kernel.org # v4.0+

locking/static_keys: Add a new static_key interface

2015-08-03T09:34:15Z

There are various problems and short-comings with the current static_key interface: - static_key_{true,false}() read like a branch depending on the key value, instead of the actual likely/unlikely branch depending on init value. - static_key_{true,false}() are, as stated above, tied to the static_key init values STATIC_KEY_INIT_{TRUE,FALSE}. - we're limited to the 2 (out of 4) possible options that compile to a default NOP because that's what our arch_static_branch() assembly emits. So provide a new static_key interface: DEFINE_STATIC_KEY_TRUE(name); DEFINE_STATIC_KEY_FALSE(name); Which define a key of different types with an initial true/false value. Then allow: static_branch_likely() static_branch_unlikely() to take a key of either type and emit the right instruction for the case. This means adding a second arch_static_branch_jump() assembly helper which emits a JMP per default. In order to determine the right instruction for the right state, encode the branch type in the LSB of jump_entry::key. This is the final step in removing the naming confusion that has led to a stream of avoidable bugs such as: a833581e372a ("x86, perf: Fix static_key bug in load_mm_cr4()") ... but it also allows new static key combinations that will give us performance enhancements in the subsequent patches. Tested-by: Rabin Vincent # arm Signed-off-by: Peter Zijlstra (Intel) Acked-by: Michael Ellerman # ppc Acked-by: Heiko Carstens # s390 Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

jump_label: Allow asm/jump_label.h to be included in assembly

2015-04-09T07:40:23Z

Wrap asm/jump_label.h for all archs with #ifndef __ASSEMBLY__. Since these are kernel only headers, we don't need #ifdef __KERNEL__ so can simplify things a bit. If an architecture wants to use jump labels in assembly, it will still need to define a macro to create the __jump_table entries (see ARCH_STATIC_BRANCH in the powerpc asm/jump_label.h for an example). Signed-off-by: Anton Blanchard Acked-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: benh@kernel.crashing.org Cc: catalin.marinas@arm.com Cc: davem@davemloft.net Cc: heiko.carstens@de.ibm.com Cc: jbaron@akamai.com Cc: linux@arm.linux.org.uk Cc: linuxppc-dev@lists.ozlabs.org Cc: liuj97@gmail.com Cc: mgorman@suse.de Cc: mmarek@suse.cz Cc: mpe@ellerman.id.au Cc: paulus@samba.org Cc: ralf@linux-mips.org Cc: rostedt@goodmis.org Cc: schwidefsky@de.ibm.com Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1428551492-21977-1-git-send-email-anton@samba.org Signed-off-by: Ingo Molnar

MIPS: jump_label.c: Handle the microMIPS J instruction encoding

2014-11-19T17:22:09Z

Implement the microMIPS encoding of the J instruction for the purpose of the static keys feature, fixing a crash early on in bootstrap as the kernel is unhappy seeing the ISA bit set in jump table entries. Make sure the ISA bit correctly reflects the instruction encoding chosen for the kernel, 0 for the standard MIPS and 1 for the microMIPS encoding. Also make sure the instruction to patch is a 32-bit NOP in the microMIPS mode as by default the 16-bit short encoding is assumed Signed-off-by: Maciej W. Rozycki Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/8516/ Signed-off-by: Ralf Baechle