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Message-ID: <20250710163522.3195293-9-jremus@linux.ibm.com>
Date: Thu, 10 Jul 2025 18:35:14 +0200
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
bpf@...r.kernel.org, x86@...nel.org,
Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Ilya Leoshkevich <iii@...ux.ibm.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Andrii Nakryiko <andrii@...nel.org>,
Indu Bhagat <indu.bhagat@...cle.com>,
"Jose E. Marchesi" <jemarch@....org>,
Beau Belgrave <beaub@...ux.microsoft.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>,
Sam James <sam@...too.org>
Subject: [RFC PATCH v1 08/16] unwind_user: Enable archs that save RA/FP in other registers
Enable unwinding of user space for architectures, such as s390, that
save the return address (RA) and/or frame pointer (FP) in other
registers. This is only valid in the topmost frame, for instance when
in a leaf function.
Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
arch/Kconfig | 7 ++++
arch/x86/include/asm/unwind_user.h | 24 +++++++++---
include/asm-generic/unwind_user.h | 20 ++++++++++
include/asm-generic/unwind_user_sframe.h | 24 ++++++++++++
include/linux/unwind_user_types.h | 18 ++++++++-
kernel/unwind/sframe.c | 4 +-
kernel/unwind/user.c | 47 ++++++++++++++++++++----
7 files changed, 126 insertions(+), 18 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 367eaf7e62e0..9e28dffe42cb 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -455,6 +455,13 @@ config HAVE_USER_RA_REG
help
The arch passes the return address (RA) in user space in a register.
+config HAVE_UNWIND_USER_LOC_REG
+ bool
+ help
+ The arch potentially saves the return address (RA) and/or frame
+ pointer (FP) register values in user space in other registers, when
+ in the topmost frame (e.g. in leaf function).
+
config SFRAME_VALIDATION
bool "Enable .sframe section debugging"
depends on HAVE_UNWIND_USER_SFRAME
diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index c2881840adf4..925d208aa39d 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -5,18 +5,30 @@
#include <linux/unwind_user_types.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, \
+ .cfa_off = (s32)sizeof(long) * 2, \
+ .ra = { \
+ .loc = UNWIND_USER_LOC_STACK, \
+ .frame_off = (s32)sizeof(long) * -1, \
+ }, \
+ .fp = { \
+ .loc = UNWIND_USER_LOC_STACK, \
+ .frame_off = (s32)sizeof(long) * -2, \
+ }, \
.sp_val_off = (s32)0, \
.use_fp = true,
#ifdef CONFIG_IA32_EMULATION
#define ARCH_INIT_USER_COMPAT_FP_FRAME \
- .cfa_off = (s32)sizeof(u32) * 2, \
- .ra_off = (s32)sizeof(u32) * -1, \
- .fp_off = (s32)sizeof(u32) * -2, \
+ .cfa_off = (s32)sizeof(u32) * 2, \
+ .ra = { \
+ .loc = UNWIND_USER_LOC_STACK, \
+ .frame_off = (s32)sizeof(u32) * -1, \
+ }, \
+ .fp = { \
+ .loc = UNWIND_USER_LOC_STACK, \
+ .frame_off = (s32)sizeof(u32) * -2, \
+ }, \
.sp_val_off = (s32)0, \
.use_fp = true,
diff --git a/include/asm-generic/unwind_user.h b/include/asm-generic/unwind_user.h
index b8882b909944..3891b7cfe3b8 100644
--- a/include/asm-generic/unwind_user.h
+++ b/include/asm-generic/unwind_user.h
@@ -2,4 +2,24 @@
#ifndef _ASM_GENERIC_UNWIND_USER_H
#define _ASM_GENERIC_UNWIND_USER_H
+#include <asm/unwind_user_types.h>
+
+#ifndef unwind_user_get_reg
+
+/**
+ * generic_unwind_user_get_reg - Get register value.
+ * @val: Register value.
+ * @regnum: DWARF register number to obtain the value from.
+ *
+ * Returns zero if successful. Otherwise -EINVAL.
+ */
+static inline int generic_unwind_user_get_reg(unsigned long *val, int regnum)
+{
+ return -EINVAL;
+}
+
+#define unwind_user_get_reg generic_unwind_user_get_reg
+
+#endif /* !unwind_user_get_reg */
+
#endif /* _ASM_GENERIC_UNWIND_USER_H */
diff --git a/include/asm-generic/unwind_user_sframe.h b/include/asm-generic/unwind_user_sframe.h
index 6c87a7f29861..8cef3e0857b6 100644
--- a/include/asm-generic/unwind_user_sframe.h
+++ b/include/asm-generic/unwind_user_sframe.h
@@ -2,8 +2,31 @@
#ifndef _ASM_GENERIC_UNWIND_USER_SFRAME_H
#define _ASM_GENERIC_UNWIND_USER_SFRAME_H
+#include <linux/unwind_user_types.h>
#include <linux/types.h>
+/**
+ * generic_sframe_set_frame_reginfo - Populate info to unwind FP/RA register
+ * from SFrame offset.
+ * @reginfo: Unwind info for FP/RA register.
+ * @offset: SFrame offset value.
+ *
+ * A non-zero offset value denotes a stack offset from CFA and indicates
+ * that the register is saved on the stack. A zero offset value indicates
+ * that the register is not saved.
+ */
+static inline void generic_sframe_set_frame_reginfo(
+ struct unwind_user_reginfo *reginfo,
+ s32 offset)
+{
+ if (offset) {
+ reginfo->loc = UNWIND_USER_LOC_STACK;
+ reginfo->frame_off = offset;
+ } else {
+ reginfo->loc = UNWIND_USER_LOC_NONE;
+ }
+}
+
/**
* generic_sframe_sp_val_off - Get generic SP value offset from CFA.
*
@@ -25,6 +48,7 @@ static inline s32 generic_sframe_sp_val_off(void)
return 0;
}
+#define sframe_set_frame_reginfo generic_sframe_set_frame_reginfo
#define sframe_sp_val_off generic_sframe_sp_val_off
#endif /* _ASM_GENERIC_UNWIND_USER_SFRAME_H */
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index adef01698bb3..57fd16e314cf 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -21,10 +21,24 @@ struct unwind_stacktrace {
unsigned long *entries;
};
+enum unwind_user_loc {
+ UNWIND_USER_LOC_NONE,
+ UNWIND_USER_LOC_STACK,
+ UNWIND_USER_LOC_REG,
+};
+
+struct unwind_user_reginfo {
+ enum unwind_user_loc loc;
+ union {
+ s32 frame_off;
+ int regnum;
+ };
+};
+
struct unwind_user_frame {
s32 cfa_off;
- s32 ra_off;
- s32 fp_off;
+ struct unwind_user_reginfo ra;
+ struct unwind_user_reginfo fp;
s32 sp_val_off;
bool use_fp;
};
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 5bfaf06e6cd2..43ef3a8c4c26 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -314,8 +314,8 @@ static __always_inline int __find_fre(struct sframe_section *sec,
}
frame->cfa_off = fre->cfa_off;
- frame->ra_off = fre->ra_off;
- frame->fp_off = fre->fp_off;
+ sframe_set_frame_reginfo(&frame->ra, fre->ra_off);
+ sframe_set_frame_reginfo(&frame->fp, fre->fp_off);
frame->use_fp = SFRAME_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
frame->sp_val_off = sframe_sp_val_off();
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 03a6da36192f..ee00d39d2a8e 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -98,26 +98,57 @@ static int unwind_user_next(struct unwind_user_state *state)
/* Get the Return Address (RA) */
- if (frame->ra_off) {
+ switch (frame->ra.loc) {
+ case UNWIND_USER_LOC_NONE:
+ if (!IS_ENABLED(CONFIG_HAVE_USER_RA_REG) || !topmost)
+ goto done;
+ ra = user_return_address(task_pt_regs(current));
+ break;
+ case UNWIND_USER_LOC_STACK:
+ if (!frame->ra.frame_off)
+ goto done;
/* Make sure that the address is word aligned */
shift = sizeof(long) == 4 || compat_fp_state(state) ? 2 : 3;
- if ((cfa + frame->ra_off) & ((1 << shift) - 1))
+ if ((cfa + frame->ra.frame_off) & ((1 << shift) - 1))
goto done;
- if (unwind_get_user_long(ra, cfa + frame->ra_off, state))
+ if (unwind_get_user_long(ra, cfa + frame->ra.frame_off, state))
goto done;
- } else {
- if (!IS_ENABLED(CONFIG_HAVE_USER_RA_REG) || !topmost)
+ break;
+ case UNWIND_USER_LOC_REG:
+ if (!IS_ENABLED(CONFIG_HAVE_UNWIND_USER_LOC_REG) || !topmost)
goto done;
- ra = user_return_address(task_pt_regs(current));
+ if (unwind_user_get_reg(&ra, frame->ra.regnum))
+ goto done;
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ goto done;
}
/* Get the Frame Pointer (FP) */
- if (frame->fp_off && unwind_get_user_long(fp, cfa + frame->fp_off, state))
+ switch (frame->fp.loc) {
+ case UNWIND_USER_LOC_NONE:
+ break;
+ case UNWIND_USER_LOC_STACK:
+ if (!frame->fp.frame_off)
+ goto done;
+ if (unwind_get_user_long(fp, cfa + frame->fp.frame_off, state))
+ goto done;
+ break;
+ case UNWIND_USER_LOC_REG:
+ if (!IS_ENABLED(CONFIG_HAVE_UNWIND_USER_LOC_REG) || !topmost)
+ goto done;
+ if (unwind_user_get_reg(&fp, frame->fp.regnum))
+ goto done;
+ break;
+ default:
+ WARN_ON_ONCE(1);
goto done;
+ }
state->ip = ra;
state->sp = sp;
- if (frame->fp_off)
+ if (frame->fp.loc != UNWIND_USER_LOC_NONE)
state->fp = fp;
arch_unwind_user_next(state);
--
2.48.1
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