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author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2023-01-03 09:56:28 -0300 |
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committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2023-01-12 13:54:34 -0300 |
commit | 7e31d166510ac4adbf53d5e8144c709a37dd8c7a (patch) | |
tree | 426190b8999a58352719ef05b4003d79caf091ae /csu/libc-start.c | |
parent | 402853be1db5a233ec688f8c5343b73191629fbd (diff) | |
download | glibc-7e31d166510ac4adbf53d5e8144c709a37dd8c7a.tar.gz glibc-7e31d166510ac4adbf53d5e8144c709a37dd8c7a.tar.xz glibc-7e31d166510ac4adbf53d5e8144c709a37dd8c7a.zip |
elf: Fix GL(dl_phdr) and GL(dl_phnum) for static builds [BZ #29864]
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. Reviewed-by: Florian Weimer <fweimer@redhat.com>
Diffstat (limited to 'csu/libc-start.c')
-rw-r--r-- | csu/libc-start.c | 21 |
1 files changed, 0 insertions, 21 deletions
diff --git a/csu/libc-start.c b/csu/libc-start.c index ef26a89bc4..c3bb6d09bc 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__ ((visibility ("hidden"))); -# else - __attribute__ ((weak, visibility ("hidden"))); - if (&__ehdr_start != NULL) -# endif - { - assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr)); - GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff; - GL(dl_phnum) = __ehdr_start.e_phnum; - } - } __tunables_init (__environ); |