diff --git a/find-provides.ksyms b/find-provides.ksyms index d498598..5212196 100755 --- a/find-provides.ksyms +++ b/find-provides.ksyms @@ -37,6 +37,63 @@ for module in $(grep -E '/lib/modules/.+\.ko(\.gz|\.bz2|\.xz|\.zst)?$') "$@"; do module="$tmpfile" fi + # A modversion can be stored as an ELF symbol in various ways: + # - An immediate symbol whose value is available directly; it shows up + # in the nm output, for example: + # $ nm mlx5_core_5.14.x86_64.ko | grep '__crc_' | head -n 3 + # 0000000092f175ca A __crc_mlx5_access_reg + # 000000005b88c9f1 A __crc_mlx5_add_flow_rules + # 00000000e7c0ec8a A __crc_mlx5_alloc_bfreg + # $ zgrep mlx5_access_reg ./lib/modules/5.14.0-284.15.1.el9_2.x86_64/symvers.gz + # 0x92f175ca mlx5_access_reg drivers/net/ethernet/mellanox/mlx5/core/mlx5_core EXPORT_SYMBOL_GPL + # This approach was being used on x86 and arm before Linux 5.19, + # for example. + # + # - A globally or locally visible symbol in a read-only (or not; + # sometimes .rodata is not a read-only section, after all, as binutils + # commit binutils-2_33~1385 has revealed (and binutils-2_35~1768 hasn't + # concealed back)) section (historically .rodata, __kcrctab/__kcrctab_gpl + # since Linux v5.19-rc1~139^2~2): + # $ nm mlx5_core_5.14.s390x.ko | grep '__crc_' | head -n 3 + # 0000000000002f7c R __crc_mlx5_access_reg + # 0000000000003304 R __crc_mlx5_add_flow_rules + # 0000000000002d2c R __crc_mlx5_alloc_bfreg + # This layout is used on ppc since Linux v4.10-rc7~15^2~1, for example, + # and on all architectures since Linux 5.19. To extract the symbol + # versions in this case, we get the offset and the section name + # from the "objdump -t" output: + # $ objdump -t lib/modules/mlx5_core_5.14.s390x.ko | grep '__crc_' | sort -k 5,5 | head -n 2 + # 0000000000002f7c g .rodata 0000000000000000 __crc_mlx5_access_reg + # 0000000000003304 g .rodata 0000000000000000 __crc_mlx5_add_flow_rules + # and the section contents from the "readelf -R" call: + # $ readelf -R .rodata mlx5_core_5.14.s390x.ko + # [... skipped output ...] + # 0x00002f70 6c6f635f 6e6f6465 00000000 ed6560a8 loc_node.....e`. + # ^^^^^^^^ + # comparison with the contents + # of lib/modules/5.14.0-284.15.1.el9_2.s390x/symvers.gz corroborates + # its correctness: + # 0xed6560a8 mlx5_access_reg drivers/net/ethernet/mellanox/mlx5/core/mlx5_core EXPORT_SYMBOL_GPL + # As mentioned earlier, for the later kernel versions, __kcrctab{,_gpl} + # sections are used: + # $ objdump -t lib/modules/mlx5_core_6.4.x86_64.ko | grep '__crc_' | sort -k 5,5 | head -n 2 + # 0000000000000000 l __kcrctab_gpl 0000000000000000 __crc_mlx5_access_reg + # 0000000000000090 l __kcrctab 0000000000000000 __crc_mlx5_add_flow_rules + # $ readelf -R __kcrctab_gpl mlx5_core_6.4.x86_64.ko + # 0x00000000 38b0d3c3 1840ce35 b99babc7 70b4700c 8....@.5....p.p. + # ^^^^^^^^ + # and in lib/modules/6.4.0-0.rc1.20230511git80e62bc8487b.19.eln126.x86_64/symvers.xz + # we see that it is correct (when accounted for the little endianness): + # 0xc3d3b038 mlx5_access_reg drivers/net/ethernet/mellanox/mlx5/core/mlx5_core EXPORT_SYMBOL_GPL + # This data, after some post-processing, can be used in the awk script + # that extracts parts of the section according to the offsets got + # from the "objdump -t" output. + # + # An important assumption here is that all the __crc_* symbols in a kmod + # are either absolute or relative ones (and this one has been held so far, + # and supposedly will in the future, as the symbols are universally + # non-immediate now). + # awk script return code: # 0 - absolute __crc_* symbols have been found, output has been # generated;