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| author | Marco Elver <elver@google.com> | 2026-05-11 22:16:59 +0200 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2026-05-19 13:02:00 +0100 |
| commit | d54e4fde9de2b8670788fd3bb4daf31cf1cb1622 (patch) | |
| tree | 99bfc2b787009ac8fe6535eb026bf3a56f4ad1f8 | |
| parent | 7dc6922f7fdd3496de4e7d8fb99284fc08f98003 (diff) | |
| download | linux-d54e4fde9de2b8670788fd3bb4daf31cf1cb1622.tar.gz linux-d54e4fde9de2b8670788fd3bb4daf31cf1cb1622.zip | |
arm64: Implement _THIS_IP_ using inline asm
Both GCC [1] and Clang [2] consider the generic version of _THIS_IP_ to
be broken:
#define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; })
In particular, the address of a label is only expected to be used with a
computed goto.
While the generic version more or less works today, it is known to be
brittle and may break with current and future optimizations. For
example, Clang -O2 always returns 1 when this function is inlined:
static inline unsigned long get_ip(void)
{ return ({ __label__ __here; __here: (unsigned long)&&__here; }); }
Fix it by overriding _THIS_IP_ in <asm/linkage.h> (which is included by
<linux/instruction_pointer.h>) using an architecture-specific inline asm
version. Additionally, avoiding taking the address of a label prevents
compilers from emitting spurious indirect branch targets (e.g. ENDBR or
BTI) under control-flow integrity schemes.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
Link: https://github.com/llvm/llvm-project/issues/138272 [2]
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
| -rw-r--r-- | arch/arm64/include/asm/linkage.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h index 40bd17add539..73eabc82a6bb 100644 --- a/arch/arm64/include/asm/linkage.h +++ b/arch/arm64/include/asm/linkage.h @@ -43,4 +43,6 @@ SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \ bti c ; +#define _THIS_IP_ ({ unsigned long __ip; asm volatile("adr %0, ." : "=r" (__ip)); __ip; }) + #endif |