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Message-ID: <20251023160545.549532-1-jremus@linux.ibm.com>
Date: Thu, 23 Oct 2025 18:05:44 +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, linux-mm@...ck.org,
Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
Jiri Olsa <jolsa@...nel.org>,
Arnaldo Carvalho de Melo <acme@...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>,
Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
"Carlos O'Donell" <codonell@...hat.com>, Sam James <sam@...too.org>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Hildenbrand <david@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Michal Hocko <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>, Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>
Subject: [RFC PATCH 1/2] fixup! unwind_user/sframe: Add support for reading .sframe contents
This RFC fixup is POC to demonstrate how the SFrame reading code
could benefit from introducing an internal FDE representation (struct
sframe_fde_internal) similar to the used internal FRE representation
(struct sframe_fre). The goal is to eliminate the passing through of
fde_start_base in many places as well as the various computations of the
effective function start address (= *fde_start_base + fde->start_addr)
throughout this module. The internal FDE representation simply conveys
the effective function start address via the "unsigned long
func_start_addr" field.
Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
kernel/unwind/sframe.c | 52 ++++++++++++++++++++++++++----------------
1 file changed, 32 insertions(+), 20 deletions(-)
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 3d7ac4eaa8b7..f88fc2c92c58 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -17,6 +17,15 @@
#include "sframe.h"
#include "sframe_debug.h"
+struct sframe_fde_internal {
+ unsigned long func_start_addr;
+ u32 func_size;
+ u32 fres_off;
+ u32 fres_num;
+ u8 info;
+ u8 rep_size;
+};
+
struct sframe_fre {
unsigned int size;
u32 ip_off;
@@ -45,20 +54,26 @@ static __always_inline unsigned char offset_size_enum_to_size(unsigned char off_
static __always_inline int __read_fde(struct sframe_section *sec,
unsigned int fde_num,
- struct sframe_fde *fde,
- unsigned long *fde_start_base)
+ struct sframe_fde_internal *fde)
{
- unsigned long fde_addr, ip;
+ unsigned long fde_addr, func_addr;
+ struct sframe_fde _fde;
fde_addr = sec->fdes_start + (fde_num * sizeof(struct sframe_fde));
- unsafe_copy_from_user(fde, (void __user *)fde_addr,
+ unsafe_copy_from_user(&_fde, (void __user *)fde_addr,
sizeof(struct sframe_fde), Efault);
- ip = fde_addr + fde->start_addr;
- if (ip < sec->text_start || ip > sec->text_end)
+ func_addr = fde_addr + _fde.start_addr;
+ if (func_addr < sec->text_start || func_addr > sec->text_end)
return -EINVAL;
- *fde_start_base = fde_addr;
+ fde->func_start_addr = func_addr;
+ fde->func_size = _fde.func_size;
+ fde->fres_off = _fde.fres_off;
+ fde->fres_num = _fde.fres_num;
+ fde->info = _fde.info;
+ fde->rep_size = _fde.rep_size;
+
return 0;
Efault:
@@ -67,8 +82,7 @@ static __always_inline int __read_fde(struct sframe_section *sec,
static __always_inline int __find_fde(struct sframe_section *sec,
unsigned long ip,
- struct sframe_fde *fde,
- unsigned long *fde_start_base)
+ struct sframe_fde_internal *fde)
{
unsigned long func_addr_low = 0, func_addr_high = ULONG_MAX;
struct sframe_fde __user *first, *low, *high, *found = NULL;
@@ -109,13 +123,13 @@ static __always_inline int __find_fde(struct sframe_section *sec,
if (!found)
return -EINVAL;
- ret = __read_fde(sec, found - first, fde, fde_start_base);
+ ret = __read_fde(sec, found - first, fde);
if (ret)
return ret;
/* make sure it's not in a gap */
- if (ip < *fde_start_base + fde->start_addr ||
- ip >= *fde_start_base + fde->start_addr + fde->func_size)
+ if (ip < fde->func_start_addr ||
+ ip >= fde->func_start_addr + fde->func_size)
return -EINVAL;
return 0;
@@ -165,7 +179,7 @@ static __always_inline int __find_fde(struct sframe_section *sec,
s32: UNSAFE_GET_USER_SIGNED_INC(to, from, size, label))
static __always_inline int __read_fre(struct sframe_section *sec,
- struct sframe_fde *fde,
+ struct sframe_fde_internal *fde,
unsigned long fre_addr,
struct sframe_fre *fre)
{
@@ -244,8 +258,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
}
static __always_inline int __find_fre(struct sframe_section *sec,
- struct sframe_fde *fde,
- unsigned long fde_start_base,
+ struct sframe_fde_internal *fde,
unsigned long ip,
struct unwind_user_frame *frame)
{
@@ -257,7 +270,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
unsigned int i;
u32 ip_off;
- ip_off = ip - (fde_start_base + fde->start_addr);
+ ip_off = ip - fde->func_start_addr;
if (fde_type == SFRAME_FDE_TYPE_PCMASK)
ip_off %= fde->rep_size;
@@ -306,8 +319,7 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
{
struct mm_struct *mm = current->mm;
struct sframe_section *sec;
- struct sframe_fde fde;
- unsigned long fde_start_base;
+ struct sframe_fde_internal fde;
int ret;
if (!mm)
@@ -323,11 +335,11 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
sec->sframe_end - sec->sframe_start))
return -EFAULT;
- ret = __find_fde(sec, ip, &fde, &fde_start_base);
+ ret = __find_fde(sec, ip, &fde);
if (ret)
goto end;
- ret = __find_fre(sec, &fde, fde_start_base, ip, frame);
+ ret = __find_fre(sec, &fde, ip, frame);
end:
user_read_access_end();
--
2.48.1
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