Re: [RFC][PATCH] unwind: Add stacktrace_setup system call

[Steven Rostedt <rostedt@goodmis.org>]

I forgot to update Indu's email.

Indu, here's the patch for adding a system call to allow the dynamic loader
to add sframes for the dynamic libraries it adds.

The lore link to see the original email and thread:

  https://lore.kernel.org/all/20260429114355.6c712e6a@gandalf.local.home/

-- Steve


On Wed, 29 Apr 2026 11:43:55 -0400
Steven Rostedt <rostedt@kernel.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> [
>    This is an RFC that adds a system call for dynamic linkers to use to
>    tell the kernel where the sframe sections are when it loads dynamic
>    libraries.
> 
>    It is built on top of Jens's sframe implementation for v3:
> 
>       https://lore.kernel.org/linux-trace-kernel/20260127150554.2760964-1-jremus@linux.ibm.com/
> 
>    I have a repo with that code that this applies on top of here:
> 
>       git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git sframe/core
>        
> 
>    The name of the system call is "stacktrace_setup", but I'm not attached
>    to this name. If anyone can think of a better name I'm happy to take
>    suggestions.
> 
>    This patch is just to get the conversation going and the final result
>    may be much different. I tested this with the attached program which is a
>    major hack. I built glibc with sframe v3 support and I used readelf to
>    find the sframe size and location of glibc.
> 
>    readelf -e /work/usr/lib/libc.so.6 | grep sframe
>      [19] .sframe           GNU_SFRAME       00000000001d3fc0  001d3fc0
> 
>    Then I wrote a program that takes the above location and size of the
>    .sframe section in libc as parameters, scans /proc/self/maps to find
>    where it loaded libc and then calls this new system call with a pointer
>    to the location of the sframe along with its size, as well as where the
>    libc text is located.
> 
>    It then spins for 2 seconds, calls the system call again to remove the
>    sframe section it loaded, and spins for another 2 seconds.
> 
>    I ran perf record --call-graph fp,defer on the program and looked for
>    the do_spin() function.
> 
>    With sframe loaded:
> 
> sframe-test    1350  1396.333593:     202366 cpu/cycles/P: 
>             7fdf0ec38a44 [unknown] ([vdso])
>             5621a6b97243 get_time+0x19 (/work/c/sframe-test)
>             5621a6b9727f do_spin+0x1f (/work/c/sframe-test)
>             5621a6b975cd main+0xd4 (/work/c/sframe-test)
>             7fdf0ea26bda __libc_start_call_main+0x6a (/work/usr/lib/libc.so.6)
>             7fdf0ea26d05 __libc_start_main@@GLIBC_2.34+0x85 (/work/usr/lib/libc.so.6)
>             5621a6b97131 _start+0x21 (/work/c/sframe-test)
> 
>    After it unloads the sframe:
> 
> sframe-test    1350  1400.332902:     657582 cpu/cycles/P: 
>             7fdf0ec38a5e [unknown] ([vdso])
>             5621a6b97243 get_time+0x19 (/work/c/sframe-test)
>             5621a6b9727f do_spin+0x1f (/work/c/sframe-test)
>             5621a6b97602 main+0x109 (/work/c/sframe-test)
>             7fdf0ea26bda __libc_start_call_main+0x6a (/work/usr/lib/libc.so.6)
> 
>    As you can see, with the sframe loaded, it was able to walk further up
>    the libc library.
> 
>    Again, this is just an RFC, but I would like to get agreement on the
>    system call so that we can then update the dynamic linker to do this
>    instead of using my hack ;-)
> ]
> 
> Add a system call that can be used by dynamic linkers to tell the kernel
> where the sframe section is in memory for libraries it loads.
> 
> The system call stacktrace_setup takes 5 parameters:
> 
>   op - the type of operation to perform
>   addr_start - The virtual address of the sframe section
>   addr_length - The length of the sframe section
>   text_start - the text section the sframe represents
>   test_length - the length of the section
> 
> The current op values are:
> 
>   STACKTRACE_REGISTER_SFRAME - This registers the sframe
>   STACKTRACE_UNREGISTER_SFRAME - This removes the sframe
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
>  arch/alpha/kernel/syscalls/syscall.tbl      |  1 +
>  arch/arm/tools/syscall.tbl                  |  1 +
>  arch/arm64/tools/syscall_32.tbl             |  1 +
>  arch/m68k/kernel/syscalls/syscall.tbl       |  1 +
>  arch/microblaze/kernel/syscalls/syscall.tbl |  1 +
>  arch/mips/kernel/syscalls/syscall_n32.tbl   |  1 +
>  arch/mips/kernel/syscalls/syscall_n64.tbl   |  1 +
>  arch/mips/kernel/syscalls/syscall_o32.tbl   |  1 +
>  arch/parisc/kernel/syscalls/syscall.tbl     |  1 +
>  arch/powerpc/kernel/syscalls/syscall.tbl    |  1 +
>  arch/s390/kernel/syscalls/syscall.tbl       |  1 +
>  arch/sh/kernel/syscalls/syscall.tbl         |  1 +
>  arch/sparc/kernel/syscalls/syscall.tbl      |  1 +
>  arch/x86/entry/syscalls/syscall_32.tbl      |  1 +
>  arch/x86/entry/syscalls/syscall_64.tbl      |  1 +
>  arch/xtensa/kernel/syscalls/syscall.tbl     |  1 +
>  include/linux/syscalls.h                    |  1 +
>  include/uapi/asm-generic/unistd.h           |  5 ++-
>  include/uapi/linux/stacktrace.h             | 10 ++++++
>  kernel/sys_ni.c                             |  2 ++
>  kernel/unwind/sframe.c                      | 37 +++++++++++++++++++++
>  scripts/syscall.tbl                         |  1 +
>  22 files changed, 71 insertions(+), 1 deletion(-)
>  create mode 100644 include/uapi/linux/stacktrace.h
> 
> diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
> index f31b7afffc34..8c320029a156 100644
> --- a/arch/alpha/kernel/syscalls/syscall.tbl
> +++ b/arch/alpha/kernel/syscalls/syscall.tbl
> @@ -511,3 +511,4 @@
>  579	common	file_setattr			sys_file_setattr
>  580	common	listns				sys_listns
>  581	common	rseq_slice_yield		sys_rseq_slice_yield
> +582	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
> index 94351e22bfcf..60f9a33b2dc5 100644
> --- a/arch/arm/tools/syscall.tbl
> +++ b/arch/arm/tools/syscall.tbl
> @@ -486,3 +486,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/arm64/tools/syscall_32.tbl b/arch/arm64/tools/syscall_32.tbl
> index 62d93d88e0fe..a0bd04a23006 100644
> --- a/arch/arm64/tools/syscall_32.tbl
> +++ b/arch/arm64/tools/syscall_32.tbl
> @@ -483,3 +483,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> index 248934257101..266ec877300a 100644
> --- a/arch/m68k/kernel/syscalls/syscall.tbl
> +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> @@ -471,3 +471,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
> index 223d26303627..916294849393 100644
> --- a/arch/microblaze/kernel/syscalls/syscall.tbl
> +++ b/arch/microblaze/kernel/syscalls/syscall.tbl
> @@ -477,3 +477,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
> index 7430714e2b8f..20fec148901e 100644
> --- a/arch/mips/kernel/syscalls/syscall_n32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
> @@ -410,3 +410,4 @@
>  469	n32	file_setattr			sys_file_setattr
>  470	n32	listns				sys_listns
>  471	n32	rseq_slice_yield		sys_rseq_slice_yield
> +472	n32	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
> index 630aab9e5425..2743bbcab143 100644
> --- a/arch/mips/kernel/syscalls/syscall_n64.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
> @@ -386,3 +386,4 @@
>  469	n64	file_setattr			sys_file_setattr
>  470	n64	listns				sys_listns
>  471	n64	rseq_slice_yield		sys_rseq_slice_yield
> +472	n64	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
> index 128653112284..187eadc4a42e 100644
> --- a/arch/mips/kernel/syscalls/syscall_o32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
> @@ -459,3 +459,4 @@
>  469	o32	file_setattr			sys_file_setattr
>  470	o32	listns				sys_listns
>  471	o32	rseq_slice_yield		sys_rseq_slice_yield
> +472	o32	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> index c6331dad9461..9442a92ef0aa 100644
> --- a/arch/parisc/kernel/syscalls/syscall.tbl
> +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> @@ -470,3 +470,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index 4fcc7c58a105..005441233932 100644
> --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> @@ -562,3 +562,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	nospu	rseq_slice_yield		sys_rseq_slice_yield
> +472	nospu	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> index 09a7ef04d979..bc9894b25584 100644
> --- a/arch/s390/kernel/syscalls/syscall.tbl
> +++ b/arch/s390/kernel/syscalls/syscall.tbl
> @@ -398,3 +398,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> index 70b315cbe710..5766251b4d2d 100644
> --- a/arch/sh/kernel/syscalls/syscall.tbl
> +++ b/arch/sh/kernel/syscalls/syscall.tbl
> @@ -475,3 +475,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
> index 7e71bf7fcd14..20e7f3b856e4 100644
> --- a/arch/sparc/kernel/syscalls/syscall.tbl
> +++ b/arch/sparc/kernel/syscalls/syscall.tbl
> @@ -517,3 +517,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index f832ebd2d79b..652ede93b724 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -477,3 +477,4 @@
>  469	i386	file_setattr		sys_file_setattr
>  470	i386	listns			sys_listns
>  471	i386	rseq_slice_yield	sys_rseq_slice_yield
> +472	i386	stacktrace_setup	sys_stacktrace_setup
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index 524155d655da..5da918e912a6 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -396,6 +396,7 @@
>  469	common	file_setattr		sys_file_setattr
>  470	common	listns			sys_listns
>  471	common	rseq_slice_yield	sys_rseq_slice_yield
> +472	common	stacktrace_setup	sys_stacktrace_setup
>  
>  #
>  # Due to a historical design error, certain syscalls are numbered differently
> diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
> index a9bca4e484de..34f0de06baee 100644
> --- a/arch/xtensa/kernel/syscalls/syscall.tbl
> +++ b/arch/xtensa/kernel/syscalls/syscall.tbl
> @@ -442,3 +442,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index f5639d5ac331..fdbea39c1b38 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -999,6 +999,7 @@ asmlinkage long sys_lsm_get_self_attr(unsigned int attr, struct lsm_ctx __user *
>  asmlinkage long sys_lsm_set_self_attr(unsigned int attr, struct lsm_ctx __user *ctx,
>  				      u32 size, u32 flags);
>  asmlinkage long sys_lsm_list_modules(u64 __user *ids, u32 __user *size, u32 flags);
> +asmlinkage long sys_stacktrace_setup(void);
>  
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index a627acc8fb5f..d3f57d8454d7 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -863,8 +863,11 @@ __SYSCALL(__NR_listns, sys_listns)
>  #define __NR_rseq_slice_yield 471
>  __SYSCALL(__NR_rseq_slice_yield, sys_rseq_slice_yield)
>  
> +#define __NR_stacktrace_setup 472
> +__SYSCALL(__NR_stacktrace_setup, sys_stacktrace_setup)
> +
>  #undef __NR_syscalls
> -#define __NR_syscalls 472
> +#define __NR_syscalls 473
>  
>  /*
>   * 32 bit systems traditionally used different
> diff --git a/include/uapi/linux/stacktrace.h b/include/uapi/linux/stacktrace.h
> new file mode 100644
> index 000000000000..60b581f55995
> --- /dev/null
> +++ b/include/uapi/linux/stacktrace.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_STACKTRACE_H
> +#define _UAPI_LINUX_STACKTRACE_H
> +
> +enum stacktrace_setup_types {
> +	STACKTRACE_REGISTER_SFRAME	= 1,
> +	STACKTRACE_UNREGISTER_SFRAME	= 2,
> +};
> +
> +#endif /* _UAPI_LINUX_STACKTRACE_H */
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index add3032da16f..76998b0f811a 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -394,3 +394,5 @@ COND_SYSCALL(rseq_slice_yield);
>  
>  COND_SYSCALL(uretprobe);
>  COND_SYSCALL(uprobe);
> +
> +COND_SYSCALL(stacktrace_setup);
> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index f24997e84e05..a842038fb03b 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c
> @@ -12,8 +12,10 @@
>  #include <linux/mm.h>
>  #include <linux/string_helpers.h>
>  #include <linux/sframe.h>
> +#include <linux/syscalls.h>
>  #include <asm/unwind_user_sframe.h>
>  #include <linux/unwind_user_types.h>
> +#include <uapi/linux/stacktrace.h>
>  
>  #include "sframe.h"
>  #include "sframe_debug.h"
> @@ -838,3 +840,38 @@ void sframe_free_mm(struct mm_struct *mm)
>  
>  	mtree_destroy(&mm->sframe_mt);
>  }
> +
> +/**
> + * sys_stacktrace_setup - register an address for user space stacktrace walking.
> + * @op: Type of operation to perform
> + * @addr_start: The virtual address of the stacktrace information
> + * @addr_length: The length of the stacktrace information
> + * @text_start: The virtual address of the text that @addr_start represents
> + * @text_length: The length of teh text
> + *
> + * This system call is used by dynamic library utilities to inform the kernel
> + * of meta data that it loaded that can be used by the kernel to know how
> + * to stack walk the given text locations.
> + *
> + * Currently only sframes are supported, but in the future, this may be used
> + * to tell the kernel about JIT code which will most likely have a different
> + * format.
> + *
> + * The type command may be extended and parameters may be used for other
> + * purposes.
> + *
> + * Return: 0 if successful, otherwise a negative error.
> + */
> +SYSCALL_DEFINE5(stacktrace_setup, int, op, unsigned long, addr_start,
> +		unsigned long, addr_length, unsigned long, text_start,
> +		unsigned long, text_length)
> +{
> +	switch (op) {
> +	case STACKTRACE_REGISTER_SFRAME:
> +		return sframe_add_section(addr_start, addr_start + addr_length,
> +					  text_start, text_start+text_length);
> +	case STACKTRACE_UNREGISTER_SFRAME:
> +		return sframe_remove_section(addr_start);
> +	}
> +	return -EINVAL;
> +}
> diff --git a/scripts/syscall.tbl b/scripts/syscall.tbl
> index 7a42b32b6577..54a99cffeec4 100644
> --- a/scripts/syscall.tbl
> +++ b/scripts/syscall.tbl
> @@ -412,3 +412,4 @@
>  469	common	file_setattr			sys_file_setattr
>  470	common	listns				sys_listns
>  471	common	rseq_slice_yield		sys_rseq_slice_yield
> +472	common	stacktrace_setup		sys_stacktrace_setup