Re: [RFC PATCH v1 00/25] unwind_user: Implement .eh_frame handling
From: Jens Remus
Date: Wed Aug 19 2026 - 04:40:22 EST
On 8/18/2026 4:49 PM, Jens Remus wrote:
> This series adds support for parsing DWARF Call Frame Information (CFI)
> from the .eh_frame_hdr and .eh_frame sections of user space ELF files.
I am working on Sashiko's AI review feedback and will send a RFC v2
soon.
> Patch 25 adds a prctl() interface for (un)registering .eh_frame_hdr
> sections for shared libraries. I will send a related test-patch for
> Glibc separately.
Meanwhile find attached a Glibc 2.44 test patch that registers
.eh_frame_hdr sections referenced by GNU_EH_FRAME in shared libraries
with the kernel.
Regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
jremus@xxxxxxxxxx / jremus@xxxxxxxxxxxxx
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From 159003ef0ef2107ddc8ec8fd8e6ce06198ebbfdc Mon Sep 17 00:00:00 2001
From: Jens Remus <jremus@xxxxxxxxxxxxx>
Date: Wed, 19 Aug 2026 10:15:53 +0200
Subject: [PATCH] TEST: glibc: Register GNU_EH_FRAME PHDRs to the kernel
The kernel does not have direct visibility to the ELF contents of
shared libraries. In the dynamic linker register and unregister
.eh_frame_hdr sections referenced by GNU_EH_FRAME program headers
via a proposed prctl() interface [1] to the kernel, so it knows
where to find these for stacktracing purposes.
Register .eh_frame_hdr sections during shared object loading and
during setup of VDSO. Unregister them during unmapping. Uses
proposed PR_{REGISTER|UNREGISTER}_EH_FRAME prctl.
Based on Josh Poimboeuf's respective GNU_SFRAME test patch.
[1]: [RFC PATCH v1 25/25] unwind_user/eh_frame: Add prctl() interface
for (un)registering .eh_frame_hdr sections,
https://lore.kernel.org/all/20260818144954.2320378-26-jremus@xxxxxxxxxxxxx/
[ This patch is for test purposes only. ]
Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---
elf/dl-load.c | 46 ++++++++++++++++++++++++++++++++++++++++-
elf/dl-unmap-segments.h | 30 +++++++++++++++++++++++++++
elf/setup-vdso.h | 40 +++++++++++++++++++++++++++++++++++
include/link.h | 3 +++
4 files changed, 118 insertions(+), 1 deletion(-)
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 95404adae942..10ef365bc81b 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -29,6 +29,7 @@
#include <bits/wordsize.h>
#include <sys/mman.h>
#include <sys/param.h>
+#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <gnu/lib-names.h>
@@ -65,6 +66,23 @@
#define STRING(x) __STRING (x)
+#ifndef _FUTURE_LINUX_EH_FRAME
+#define _FUTURE_LINUX_EH_FRAME
+
+/* From <linux/prctl.h>. */
+#define PR_REGISTER_EH_FRAME 82
+#define PR_UNREGISTER_EH_FRAME 83
+
+/* From <linux/eh_frame.h>. */
+struct eh_frame_setup {
+ __u64 eh_frame_hdr_start;
+ __u64 eh_frame_hdr_size;
+ __u64 text_start;
+ __u64 text_size;
+};
+
+#endif /* _FUTURE_LINUX_EH_FRAME */
+
/* This is the decomposed LD_LIBRARY_PATH search path. */
struct r_search_path_struct __rtld_env_path_list attribute_relro;
@@ -1096,6 +1114,11 @@ _dl_map_object_scan_phdrs (struct dl_pt_load_iterator *it,
l->l_relro_addr = ph->p_vaddr;
l->l_relro_size = ph->p_memsz;
break;
+
+ case PT_GNU_EH_FRAME:
+ l->l_eh_frame_start = ph->p_vaddr;
+ l->l_eh_frame_size = ph->p_memsz;
+ break;
}
}
@@ -1384,13 +1407,34 @@ cannot enable executable stack as shared object requires");
if (l->l_tls_initimage != NULL)
l->l_tls_initimage = (void*)((uintptr_t)l->l_tls_initimage + l->l_addr);
+ /* Adjust the address of the .eh_frame_hdr start address. */
+ if (l->l_eh_frame_start != 0)
+ l->l_eh_frame_start += l->l_addr;
+
/* Process program headers again after load segments are mapped in
case processing requires accessing those segments. Scan program
headers backward since PT_GNU_PROPERTY is close to the end of
program headers. */
for (ph = &l->l_phdr[l->l_phnum]; ph != l->l_phdr; --ph)
- if (ph[-1].p_type == PT_GNU_PROPERTY)
+ switch (ph[-1].p_type)
{
+ case PT_LOAD:
+ if (l->l_eh_frame_start != 0
+ && ph[-1].p_flags & PF_X)
+ {
+ ElfW(Addr) text_start = l->l_addr + ph[-1].p_vaddr;
+ size_t text_size = ph[-1].p_memsz;
+ struct eh_frame_setup data = {
+ .eh_frame_hdr_start = l->l_eh_frame_start,
+ .eh_frame_hdr_size = l->l_eh_frame_size,
+ .text_start = text_start,
+ .text_size = text_size,
+ };
+
+ __prctl(PR_REGISTER_EH_FRAME, &data, sizeof(data), 0, 0);
+ }
+ break;
+ case PT_GNU_PROPERTY:
_dl_process_pt_gnu_property (l, fd, &ph[-1]);
break;
}
diff --git a/elf/dl-unmap-segments.h b/elf/dl-unmap-segments.h
index c3e46d50ec72..eae0843e85a8 100644
--- a/elf/dl-unmap-segments.h
+++ b/elf/dl-unmap-segments.h
@@ -21,6 +21,24 @@
#include <link.h>
#include <sys/mman.h>
+#include <sys/prctl.h>
+
+#ifndef _FUTURE_LINUX_EH_FRAME
+#define _FUTURE_LINUX_EH_FRAME
+
+/* From <linux/prctl.h>. */
+#define PR_REGISTER_EH_FRAME 82
+#define PR_UNREGISTER_EH_FRAME 83
+
+/* From <linux/eh_frame.h>. */
+struct eh_frame_setup {
+ __u64 eh_frame_hdr_start;
+ __u64 eh_frame_hdr_size;
+ __u64 text_start;
+ __u64 text_size;
+};
+
+#endif /* _FUTURE_LINUX_EH_FRAME */
/* _dl_map_segments ensures that any whole pages in gaps between segments
are filled in with PROT_NONE mappings. So we can just unmap the whole
@@ -29,6 +47,18 @@
static __always_inline void
_dl_unmap_segments (struct link_map *l)
{
+ if (l->l_eh_frame_start != 0)
+ {
+ struct eh_frame_setup data = {
+ .eh_frame_hdr_start = l->l_eh_frame_start,
+ .eh_frame_hdr_size = 0,
+ .text_start = 0,
+ .text_size = 0,
+ };
+
+ __prctl(PR_UNREGISTER_EH_FRAME, &data, sizeof(data), 0, 0);
+ }
+
__munmap ((void *) l->l_map_start, l->l_map_end - l->l_map_start);
}
diff --git a/elf/setup-vdso.h b/elf/setup-vdso.h
index 0dba7072d53b..83411c1aa396 100644
--- a/elf/setup-vdso.h
+++ b/elf/setup-vdso.h
@@ -16,6 +16,25 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+#include <sys/prctl.h>
+
+#ifndef _FUTURE_LINUX_EH_FRAME
+#define _FUTURE_LINUX_EH_FRAME
+
+/* From <linux/prctl.h>. */
+#define PR_REGISTER_EH_FRAME 82
+#define PR_UNREGISTER_EH_FRAME 83
+
+/* From <linux/eh_frame.h>. */
+struct eh_frame_setup {
+ __u64 eh_frame_hdr_start;
+ __u64 eh_frame_hdr_size;
+ __u64 text_start;
+ __u64 text_size;
+};
+
+#endif /* _FUTURE_LINUX_EH_FRAME */
+
static inline void __attribute__ ((always_inline))
setup_vdso (struct link_map *main_map __attribute__ ((unused)),
struct link_map ***first_preload __attribute__ ((unused)))
@@ -56,6 +75,14 @@ setup_vdso (struct link_map *main_map __attribute__ ((unused)),
if (ph->p_vaddr + ph->p_memsz >= l->l_map_end)
l->l_map_end = ph->p_vaddr + ph->p_memsz;
}
+ else if (ph->p_type == PT_GNU_EH_FRAME)
+ {
+ if (! l->l_eh_frame_start)
+ {
+ l->l_eh_frame_start = ph->p_vaddr;
+ l->l_eh_frame_size = ph->p_memsz;
+ }
+ }
else
/* There must be no TLS segment. */
assert (ph->p_type != PT_TLS);
@@ -78,6 +105,19 @@ setup_vdso (struct link_map *main_map __attribute__ ((unused)),
l->l_local_scope[0]->r_nlist = 1;
l->l_local_scope[0]->r_list = &l->l_real;
+ if (l->l_eh_frame_start != 0)
+ {
+ l->l_eh_frame_start += l->l_addr;
+
+ struct eh_frame_setup data = {
+ .eh_frame_hdr_start = l->l_eh_frame_start,
+ .eh_frame_hdr_size = l->l_eh_frame_size,
+ .text_start = l->l_map_start,
+ .text_size = l->l_map_end - l->l_map_start,
+ };
+ __prctl(PR_REGISTER_EH_FRAME, &data, sizeof(data), 0, 0);
+ }
+
/* Now that we have the info handy, use the DSO image's soname
so this object can be looked up by name. */
{
diff --git a/include/link.h b/include/link.h
index 8f851d2212df..b9ee4674ac69 100644
--- a/include/link.h
+++ b/include/link.h
@@ -345,6 +345,9 @@ struct link_map
ElfW(Addr) l_relro_addr;
size_t l_relro_size;
+ ElfW(Addr) l_eh_frame_start;
+ size_t l_eh_frame_size;
+
unsigned long long int l_serial;
};
--
2.53.0