MIPS support for GNU hash

System Internals / glibc - Mihailo Stojanovic [rt-rk.com] - 29 August 2019 20:11 EDT

This patch is a reimplementation of [1], which was submitted back in 2015. Copyright issue has been sorted [2] last year. It proposed a new section (.gnu.xhash) and related dynamic tag (GT_GNU_XHASH). The new section would be virtually identical to the existing .gnu.hash except for the translation table (xlat) which would contain correct MIPS .dynsym indexes corresponding to the hashvals in chains. This is because MIPS ABI imposes a different ordering of the dynsyms than the one expected by the .gnu.hash section. Another addition would be a leading word at the beggining of the section, which would contain the number of entries in the translation table.

In this patch, the new section name and dynamic tag are changed to reflect the fact that the section should be treated as MIPS specific (.MIPS.xhash and DT_MIPS_XHASH).

This patch addresses the alignment issue reported in [3] which is caused by the leading word of the .MIPS.xhash section. Leading word is now removed in the corresponding binutils patch, and the number of entries in the translation table is computed using DT_MIPS_SYMTABNO dynamic tag.

Since the MIPS specific dl-lookup.c file was removed following the initial patch submission, I opted for the definition of three new macros in the generic ldsodefs.h. ELF_MACHINE_GNU_HASH_ADDRIDX defines the index of the dynamic tag in the l_info array. ELF_MACHINE_HASH_SYMIDX is used to calculate the index of a symbol in GNU hash. On MIPS, it is defined to look up the symbol index in the translation table. ELF_MACHINE_XHASH_SETUP is defined for MIPS only. It initializes the .MIPS.xhash pointer in the link_map_machine struct.

The other major change is bumping the highest EI_ABIVERSION value for MIPS to suggest that the dynamic linker now supports GNU hash.

The patch was tested by running the glibc testsuite for the three MIPS ABIs (o32, n32 and n64) and for x86_64-linux-gnu.

[1] https://sourceware.org/ml/binutils/2015-10/msg00057.html [2] https://sourceware.org/ml/binutils/2018-03/msg00025.html [3] https://sourceware.org/ml/binutils/2016-01/msg00006.html

- elf/dl-addr.c (determine_info): Calculate the symbol index using the newly defined ELF_MACHINE_HASH_SYMIDX macro.
- elf/dl-lookup.c (do_lookup_x): Ditto. (_dl_setup_hash): Initialize MIPS xhash translation table.
- elf/elf.h (SHT_MIPS_XHASH): New define. (DT_MIPS_XHASH): New define.
- sysdeps/generic/ldsodefs.h (ELF_MACHINE_GNU_HASH_ADDRIDX): New define. (ELF_MACHINE_HASH_SYMIDX): Ditto. (ELF_MACHINE_XHASH_SETUP): Ditto.
- sysdeps/mips/ldsodefs.h (ELF_MACHINE_GNU_HASH_ADDRIDX): New define. (ELF_MACHINE_HASH_SYMIDX): Ditto. (ELF_MACHINE_XHASH_SETUP): Ditto.
- sysdeps/mips/linkmap.h (struct link_map_machine): New member.
- sysdeps/unix/sysv/linux/mips/ldsodefs.h: Increment valid ABI
- sysdeps/unix/sysv/linux/mips/libc-abis: New ABI version.

23c1c256ae MIPS support for GNU hash
ChangeLog | 21 +++++++++++++++++++++
elf/dl-addr.c | 5 ++---
elf/dl-lookup.c | 10 +++++++---
elf/elf.h | 5 ++++-
sysdeps/generic/ldsodefs.h | 17 +++++++++++++++++
sysdeps/mips/ldsodefs.h | 15 +++++++++++++++
sysdeps/mips/linkmap.h | 1 +
sysdeps/unix/sysv/linux/mips/ldsodefs.h | 2 +-
sysdeps/unix/sysv/linux/mips/libc-abis | 2 ++
9 files changed, 70 insertions(+), 8 deletions(-)

Upstream: sourceware.org

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