From: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx> Starting with gcc 11.3, the C compiler will generate PLT-relative function calls even if they are local and do not require it. Later on during linking, the linker will replace all PLT-relative calls to local functions with PC-relative ones. Unfortunately, the purgatory code of kexec/kdump is not being linked as a regular executable or shared library would have been, and therefore, all PLT-relative addresses remain in the generated purgatory object code unresolved. This in turn lets kexec-tools fail with "Unknown rela relocation: 0x14 0x73c0901c" for such relocation types. Furthermore, the clang C compiler has always behaved like described above and this commit should fix the purgatory code built with the latter. Because the purgatory code is no regular executable or shared library, contains only calls to local functions and has no PLT, all R_390_PLT32DBL relocation entries can be resolved just like a R_390_PC32DBL one. * https://refspecs.linuxfoundation.org/ELF/zSeries/lzsabi0_zSeries/x1633.html#AEN1699 Relocation entries of purgatory code generated with gcc 11.3 ------------------------------------------------------------ $ readelf -r purgatory/purgatory.o Relocation section '.rela.text' at offset 0x6e8 contains 27 entries: Offset Info Type Sym. Value Sym. Name + Addend 00000000000c 000300000013 R_390_PC32DBL 0000000000000000 .data + 2 00000000001a 001000000014 R_390_PLT32DBL 0000000000000000 sha256_starts + 2 000000000030 001100000014 R_390_PLT32DBL 0000000000000000 sha256_update + 2 000000000046 001200000014 R_390_PLT32DBL 0000000000000000 sha256_finish + 2 000000000050 000300000013 R_390_PC32DBL 0000000000000000 .data + 102 00000000005a 001300000014 R_390_PLT32DBL 0000000000000000 memcmp + 2 ... 000000000118 001600000014 R_390_PLT32DBL 0000000000000000 setup_arch + 2 00000000011e 000300000013 R_390_PC32DBL 0000000000000000 .data + 2 00000000012c 000f00000014 R_390_PLT32DBL 0000000000000000 verify_sha256_digest + 2 000000000142 001700000014 R_390_PLT32DBL 0000000000000000 post_verification[...] + 2 Relocation entries of purgatory code generated with gcc 11.2 ------------------------------------------------------------ $ readelf -r purgatory/purgatory.o Relocation section '.rela.text' at offset 0x6e8 contains 27 entries: Offset Info Type Sym. Value Sym. Name + Addend 00000000000e 000300000013 R_390_PC32DBL 0000000000000000 .data + 2 00000000001c 001000000013 R_390_PC32DBL 0000000000000000 sha256_starts + 2 000000000036 001100000013 R_390_PC32DBL 0000000000000000 sha256_update + 2 000000000048 001200000013 R_390_PC32DBL 0000000000000000 sha256_finish + 2 000000000052 000300000013 R_390_PC32DBL 0000000000000000 .data + 102 00000000005c 001300000013 R_390_PC32DBL 0000000000000000 memcmp + 2 ... 00000000011a 001600000013 R_390_PC32DBL 0000000000000000 setup_arch + 2 000000000120 000300000013 R_390_PC32DBL 0000000000000000 .data + 122 000000000130 000f00000013 R_390_PC32DBL 0000000000000000 verify_sha256_digest + 2 000000000146 001700000013 R_390_PC32DBL 0000000000000000 post_verification[...] + 2 Corresponding s390 kernel discussion: * https://lore.kernel.org/linux-s390/20211208105801.188140-1-egorenar@xxxxxxxxxxxxx/T/#u Signed-off-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx> Reported-by: Tao Liu <ltao@xxxxxxxxxx> Suggested-by: Philipp Rudo <prudo@xxxxxxxxxx> Reviewed-by: Philipp Rudo <prudo@xxxxxxxxxx> [hca@xxxxxxxxxxxxx: changed commit message as requested by Philipp Rudo] Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx> --- kexec/arch/s390/kexec-elf-rel-s390.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kexec/arch/s390/kexec-elf-rel-s390.c b/kexec/arch/s390/kexec-elf-rel-s390.c index a5e1b7345578..91ba86a9991d 100644 --- a/kexec/arch/s390/kexec-elf-rel-s390.c +++ b/kexec/arch/s390/kexec-elf-rel-s390.c @@ -56,6 +56,7 @@ void machine_apply_elf_rel(struct mem_ehdr *UNUSED(ehdr), case R_390_PC16: /* PC relative 16 bit. */ case R_390_PC16DBL: /* PC relative 16 bit shifted by 1. */ case R_390_PC32DBL: /* PC relative 32 bit shifted by 1. */ + case R_390_PLT32DBL: /* 32 bit PC rel. PLT shifted by 1. */ case R_390_PC32: /* PC relative 32 bit. */ case R_390_PC64: /* PC relative 64 bit. */ val -= address; @@ -63,7 +64,7 @@ void machine_apply_elf_rel(struct mem_ehdr *UNUSED(ehdr), *(unsigned short *) loc = val; else if (r_type == R_390_PC16DBL) *(unsigned short *) loc = val >> 1; - else if (r_type == R_390_PC32DBL) + else if (r_type == R_390_PC32DBL || r_type == R_390_PLT32DBL) *(unsigned int *) loc = val >> 1; else if (r_type == R_390_PC32) *(unsigned int *) loc = val; -- 2.32.0 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
