Hi Alexander, @Alexander: Thanks for taking care of this. On Wed, 8 Dec 2021 13:53:55 +0100 Alexander Egorenkov <egorenar@xxxxxxxxxxxxx> wrote: > 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 leads to the situation where the purgatory > code is being executed during kdump with all PLT-relative addresses > unresolved. And this results in endless loops within the purgatory code. Tiny nit. The last two sentences describe the situation in the kernel. Luckily the kexec-tools do proper error checking and die with "Unknown rela relocation: 0x14 0x73c0901c" when they encounter an unknown relocation type. Anyway, the code is correct Reviewed-by: Philipp Rudo <prudo@xxxxxxxxxx> > 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> > --- > 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; _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
