Re: [PATCH v2 1/2] unwind_user/x86: Enable frame pointer unwinding on x86
From: Peter Zijlstra <peterz@infradead.org>
Date: 2025-09-23 10:51:36
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On Wed, Aug 27, 2025 at 03:36:45PM -0400, Steven Rostedt wrote:
quoted hunk ↗ jump to hunk
From: Josh Poimboeuf <jpoimboe@kernel.org> Use ARCH_INIT_USER_FP_FRAME to describe how frame pointers are unwound on x86, and enable CONFIG_HAVE_UNWIND_USER_FP accordingly so the unwind_user interfaces can be used. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> --- arch/x86/Kconfig | 1 + arch/x86/include/asm/unwind_user.h | 11 +++++++++++ 2 files changed, 12 insertions(+) create mode 100644 arch/x86/include/asm/unwind_user.hdiff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 58d890fe2100..8f94c58d4de8 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig@@ -299,6 +299,7 @@ config X86 select HAVE_SYSCALL_TRACEPOINTS select HAVE_UACCESS_VALIDATION if HAVE_OBJTOOL select HAVE_UNSTABLE_SCHED_CLOCK + select HAVE_UNWIND_USER_FP if X86_64 select HAVE_USER_RETURN_NOTIFIER select HAVE_GENERIC_VDSO select VDSO_GETRANDOM if X86_64diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h new file mode 100644 index 000000000000..8597857bf896 --- /dev/null +++ b/arch/x86/include/asm/unwind_user.h@@ -0,0 +1,11 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_X86_UNWIND_USER_H +#define _ASM_X86_UNWIND_USER_H + +#define ARCH_INIT_USER_FP_FRAME \ + .cfa_off = (s32)sizeof(long) * 2, \ + .ra_off = (s32)sizeof(long) * -1, \ + .fp_off = (s32)sizeof(long) * -2, \ + .use_fp = true, + +#endif /* _ASM_X86_UNWIND_USER_H */
Moo, and now you have me look at unwind/user.c:
/* Make sure that the address is word aligned */
shift = sizeof(long) == 4 ? 2 : 3;
if (cfa & ((1 << shift) - 1))
return -EINVAL;
Isn't that just:
if (cfa & (sizeof(long) - 1))
?
Let me go add a patch to clean that up...