[RFC PATCH 1/2] fixup! unwind_user/sframe: Add support for reading .sframe contents
From: Jens Remus <hidden>
Date: 2025-10-23 16:06:55
Also in:
bpf, linux-mm, lkml
Subsystem:
the rest, userspace stack unwinding · Maintainers:
Linus Torvalds, Josh Poimboeuf, Steven Rostedt
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 <redacted> --- 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