The 73fc4e28b9464f0e refactor did not add the GL(dl_phdr) and
GL(dl_phnum) for static build, relying on the __ehdr_start symbol,
which is always added by the static linker, to get the correct values.

This is problematic in some ways:

- The segment may see its in-memory size differ from its in-file
size (or the binary may have holes). The Linux has fixed is to
provide concise values for both AT_PHDR and AT_PHNUM (commit
0da1d5002745c - "fs/binfmt_elf: Fix AT_PHDR for unusual ELF files")

- Some archs (alpha for instance) the hidden weak reference is not
correctly pulled by the static linker and __ehdr_start address
end up being 0, which makes GL(dl_phdr) and GL(dl_phnum) have both
invalid values (and triggering a segfault later on libc.so while
accessing TLS variables).

The safer fix is to just restore the previous behavior to setup
GL(dl_phdr) and GL(dl_phnum) for static based on kernel auxv. The
__ehdr_start fallback can also be simplified by not assuming weak
linkage (as for PIE).

The libc-static.c auxv init logic is moved to dl-support.c, since
the later is build without SHARED and then GLRO macro is defined
to access the variables directly.

The _dl_phdr is also assumed to be always non NULL, since an invalid
NULL values does not trigger TLS initialization (which is used in
various libc systems).

Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu.
---
csu/libc-start.c | 21 ----------
csu/libc-tls.c | 25 ++++++------
elf/dl-support.c | 52 ++++++++++++++++---------
sysdeps/unix/sysv/linux/dl-parse_auxv.h | 1 +
4 files changed, 46 insertions(+), 53 deletions(-)

diff --git a/csu/libc-start.c b/csu/libc-start.c
index 543560f36c..bfeee6d851 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -262,28 +262,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
}
# endif
_dl_aux_init (auxvec);
- if (GL(dl_phdr) == NULL)
# endif
- {
- /* Starting from binutils-2.23, the linker will define the
- magic symbol __ehdr_start to point to our own ELF header
- if it is visible in a segment that also includes the phdrs.
- So we can set up _dl_phdr and _dl_phnum even without any
- information from auxv. */
-
- extern const ElfW(Ehdr) __ehdr_start
-# if BUILD_PIE_DEFAULT
- __attribute__ ((vi

* Adhemerval Zanella:

diff --git a/elf/dl-support.c b/elf/dl-support.c
index 614b5b3e0c..b5ec5bd6d1 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -250,12 +250,27 @@ _dl_aux_init (ElfW(auxv_t) *av)
#endif

_dl_auxv = av;
- dl_parse_auxv_t auxv_values;
- /* Use an explicit initialization loop here because memset may not
- be available yet. */
- for (int i = 0; i < array_length (auxv_values); ++i)
- auxv_values[i] = 0;
+ dl_parse_auxv_t auxv_values = { 0, };

Is this really safe? If so, it should still be in a separate commit.

diff --git a/sysdeps/unix/sysv/linux/dl-parse_auxv.h b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
index bf9374371e..2bf3a0ca6b 100644
--- a/sysdeps/unix/sysv/linux/dl-parse_auxv.h
+++ b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
@@ -21,6 +21,7 @@
#include <fpu_control.h>
#include <ldsodefs.h>
#include <link.h>
+#include <dl-auxv.h> /* For DL_PLATFORM_AUXV */

typedef ElfW(Addr) dl_parse_auxv_t[AT_MINSIGSTKSZ + 1];

Why is this change needed?

Thanks,
Florian

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 11/01/23 11:27, Florian Weimer wrote:

* Adhemerval Zanella:

diff --git a/elf/dl-support.c b/elf/dl-support.c
index 614b5b3e0c..b5ec5bd6d1 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -250,12 +250,27 @@ _dl_aux_init (ElfW(auxv_t) *av)
#endif

_dl_auxv = av;
- dl_parse_auxv_t auxv_values;
- /* Use an explicit initialization loop here because memset may not
- be available yet. */
- for (int i = 0; i < array_length (auxv_values); ++i)
- auxv_values[i] = 0;
+ dl_parse_auxv_t auxv_values = { 0, };

Is this really safe? If so, it should still be in a separate commit.

It should be since 5355f9ca7b10183ce06e8a18003ba30f43774858, but I will recheck. I can move it to another patch, but I think it is a lefover of
the -fno-tree-loop-distribute-patterns removal.

diff --git a/sysdeps/unix/sysv/linux/dl-parse_auxv.h b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
index bf9374371e..2bf3a0ca6b 100644
--- a/sysdeps/unix/sysv/linux/dl-parse_auxv.h
+++ b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
@@ -21,6 +21,7 @@
#include <fpu_control.h>
#include <ldsodefs.h>
#include <link.h>
+#include <dl-auxv.h> /* For DL_PLATFORM_AUXV */

typedef ElfW(Addr) dl_parse_auxv_t[AT_MINSIGSTKSZ + 1];

Why is this change needed?

Hum, it might a leftover of development. I will check.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)