From 00be69070d91d2be978e752bb117a0a4db0e1281 Mon Sep 17 00:00:00 2001 From: Saket Kumar Bhaskar Date: Mon, 3 Aug 2026 10:58:43 +0530 Subject: [PATCH] powerpc/irq: Fix missing r2 clobber in PCREL inline assembly In CONFIG_PPC_KERNEL_PCREL mode, r2 is no longer reserved for the TOC pointer and is available as a caller-saved register [0]. Both call_do_irq() and call_do_softirq() use inline assembly to call functions with stack switching, but fail to list r2 in their clobber lists. This causes the compiler to assume r2 is preserved across these calls, leading to register corruption when the called functions (__do_irq and __do_softirq) clobber r2. As a result of this kernel crash during interrupt handling is seen and the kernel fails to boot: BUG: Unable to handle kernel data access on write at 0xc000000404697638 Faulting instruction address: 0xc0000000000181ec Oops: Kernel access of bad area, sig: 11 [#1] NIP [c0000000000181ec] __do_IRQ+0x6c/0xc0 With older GCC, the compiler would conservatively allocate callee-saved registers (like r31) for values spanning function calls, accidentally avoiding the bug: <__do_IRQ>: 00 00 00 60 nop a6 02 08 7c mflr r0 f8 ff e1 fb std r31,-8(r1) f0 ff c1 fb std r30,-16(r1) 2d 03 10 06 pla r31,53297316 ... 3d e8 ff 4b bl c0000000000165ac <__do_irq> 00 00 21 e8 ld r1,0(r1) 28 00 4d e9 ld r10,40(r13) 40 00 21 38 addi r1,r1,64 2a f9 aa 7f stdx r29,r10,r31 With newer GCC 14, the compiler uses r2 for such values, exposing the missing clobber specification: <__do_IRQ>: 00 00 00 60 nop a6 02 08 7c mflr r0 f0 ff c1 fb std r30,-16(r1) f8 ff e1 fb std r31,-8(r1) 29 02 10 06 pla r2,36252592 # c0000000022aadc0 <__irq_regs> ... 85 dc ff 4b bl c000000000015ee0 <__do_irq> 00 00 21 e8 ld r1,0(r1) 28 00 2d e9 ld r9,40(r13) 30 00 21 38 addi r1,r1,48 2a 11 c9 7f stdx r30,r9,r2 Fix this by adding r2 to the clobber list for both call_do_irq() and call_do_softirq() when CONFIG_PPC_KERNEL_PCREL is enabled. [0]: https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg313226.html Fixes: 7e3a68be42e1 ("powerpc/64: vmlinux support building with PCREL addresing") Signed-off-by: Saket Kumar Bhaskar Reviewed-by: Christophe Leroy (CS GROUP) Reviewed-by: Hari Bathini Signed-off-by: Madhavan Srinivasan Link: https://patch.msgid.link/10fc2cda485cd22e209a31d786bed1984bdf3982.1785732393.git.skb99@linux.ibm.com --- arch/powerpc/kernel/irq.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c index f69de08ad347..15a3c3fd8e70 100644 --- a/arch/powerpc/kernel/irq.c +++ b/arch/powerpc/kernel/irq.c @@ -217,8 +217,12 @@ static __always_inline void call_do_softirq(const void *sp) [sp] "b" (sp), [offset] "i" (THREAD_SIZE - STACK_FRAME_MIN_SIZE), [callee] "i" (__do_softirq) : // Clobbers - "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", - "cr7", "r0", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10", + "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7", "r0", + /* r2 may be clobbered by the callee when using PCREL mode in the ELFv2 ABI. */ +#ifdef CONFIG_PPC_KERNEL_PCREL + "r2", +#endif + "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12" ); } @@ -275,8 +279,12 @@ static __always_inline void call_do_irq(struct pt_regs *regs, void *sp) [sp] "b" (sp), [offset] "i" (THREAD_SIZE - STACK_FRAME_MIN_SIZE), [callee] "i" (__do_irq) : // Clobbers - "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", - "cr7", "r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", + "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7", "r0", + /* r2 may be clobbered by the callee when using PCREL mode in the ELFv2 ABI. */ +#ifdef CONFIG_PPC_KERNEL_PCREL + "r2", +#endif + "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12" ); }