Source: glibc Version: 2.36-8 Severity: normal Tags: patch upstream User: [email protected] Usertags: alpha X-Debbugs-Cc: [email protected]
Hello! glibc fails to build from source on alpha with many testsuite failures [1] due to a regression introduced in glibc 2.34 [2]. According to the discussion on the libc-alpha mailing list, this issue affects multiple architectures for static builds. It just happens that it causes segmentation faults on alpha [3]. A proposed patch by Adhemveral Zanella has been posted on the list [4] but not been merged yet. I tested the first version of the patch [3] and can confirm that it works. I will test the posted version [4] now. Adhemerval said that he plans to backport the patch down to 2.34, so it will eventually show up in 2.36 as well. Either way, it might be a good idea to already carry the patch in Debian but I'm not sure. Thanks, Adrian > [1] https://buildd.debian.org/status/logs.php?pkg=glibc&arch=alpha > [2] https://sourceware.org/pipermail/libc-alpha/2023-January/144445.html > [3] https://sourceware.org/pipermail/libc-alpha/2023-January/144452.html > [4] https://sourceware.org/pipermail/libc-alpha/2023-January/144457.html -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer `. `' Physicist `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
--- Begin Message ---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__ ((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); diff --git a/csu/libc-tls.c b/csu/libc-tls.c index ca4def2613..51d3cf99bf 100644 --- a/csu/libc-tls.c +++ b/csu/libc-tls.c @@ -119,19 +119,18 @@ __libc_setup_tls (void) __tls_pre_init_tp (); /* Look through the TLS segment if there is any. */ - if (_dl_phdr != NULL) - for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr) - if (phdr->p_type == PT_TLS) - { - /* Remember the values we need. */ - memsz = phdr->p_memsz; - filesz = phdr->p_filesz; - initimage = (void *) phdr->p_vaddr + main_map->l_addr; - align = phdr->p_align; - if (phdr->p_align > max_align) - max_align = phdr->p_align; - break; - } + for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr) + if (phdr->p_type == PT_TLS) + { + /* Remember the values we need. */ + memsz = phdr->p_memsz; + filesz = phdr->p_filesz; + initimage = (void *) phdr->p_vaddr + main_map->l_addr; + align = phdr->p_align; + if (phdr->p_align > max_align) + max_align = phdr->p_align; + break; + } /* Calculate the size of the static TLS surplus, with 0 auditors. */ _dl_tls_static_surplus_init (0); 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, }; _dl_parse_auxv (av, auxv_values); + + _dl_phdr = (void*) auxv_values[AT_PHDR]; + _dl_phnum = auxv_values[AT_PHNUM]; + + if (_dl_phdr == NULL) + { + /* 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 attribute_hidden; + assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr)); + _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff; + _dl_phnum = __ehdr_start.e_phnum; + } + + assert (_dl_phdr != NULL); } #endif @@ -324,20 +339,19 @@ _dl_non_dynamic_init (void) if (_dl_platform != NULL) _dl_platformlen = strlen (_dl_platform); - if (_dl_phdr != NULL) - for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph) - switch (ph->p_type) - { - /* Check if the stack is nonexecutable. */ - case PT_GNU_STACK: - _dl_stack_flags = ph->p_flags; - break; - - case PT_GNU_RELRO: - _dl_main_map.l_relro_addr = ph->p_vaddr; - _dl_main_map.l_relro_size = ph->p_memsz; - break; - } + for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph) + switch (ph->p_type) + { + /* Check if the stack is nonexecutable. */ + case PT_GNU_STACK: + _dl_stack_flags = ph->p_flags; + break; + + case PT_GNU_RELRO: + _dl_main_map.l_relro_addr = ph->p_vaddr; + _dl_main_map.l_relro_size = ph->p_memsz; + break; + } call_function_static_weak (_dl_find_object_init); 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]; -- 2.34.1
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