llvm-objdump -t does not respect -j

[nathanchance]

$ make -j$(nproc) -s ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- CC=clang-11 HOSTCC=clang-11 O=out OBJDUMP=llvm-objdump-11 distclean defconfig bzImage
...
llvm-objdump-11: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump-11: warning: section '.boot.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump-11: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file
error: section .boot.preserved.data differs between vmlinux and arch/s390/boot/compressed/vmlinux
make[3]: *** [/linux/arch/s390/boot/Makefile:65: arch/s390/boot/section_cmp.boot.preserved.data] Error 1
make[3]: *** Waiting for unfinished jobs....
llvm-objdump-11: warning: section '.boot.data' mentioned in a -j/--section option, but not found in any input file
error: section .boot.data differs between vmlinux and arch/s390/boot/compressed/vmlinux
...

[nathanchance]

llvm-objdump complains that it cannot find the section but it appears there when listing the section headers and it has the same size...

$ s390x-linux-gnu-objdump -h -j .boot.preserved.data out.s390/vmlinux

out.s390/vmlinux:     file format elf64-s390

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
 22 .boot.preserved.data 00001090  000000000136b000  000000000136b000  0126c000  2**12
                  CONTENTS, ALLOC, LOAD, DATA

$ llvm-objdump -h -j .boot.preserved.data out.s390/vmlinux

out.s390/vmlinux:       file format ELF64-s390

Sections:
Idx Name                 Size     VMA              Type
 22 .boot.preserved.data 00001090 000000000136b000 DATA

$ s390x-linux-gnu-objdump -t -j .boot.preserved.data out.s390/vmlinux

out.s390/vmlinux:     file format elf64-s390

SYMBOL TABLE:
000000000136b000 l    d  .boot.preserved.data   0000000000000000 .boot.preserved.data
000000000136c040 g     O .boot.preserved.data   0000000000000008 __swsusp_reset_dma
000000000136c090 g       .boot.preserved.data   0000000000000000 _edata
000000000136b000 g     O .boot.preserved.data   0000000000001000 ipl_block
000000000136b000 g       .boot.preserved.data   0000000000000000 __boot_data_preserved_start
000000000136c020 g     O .boot.preserved.data   0000000000000008 __sdma
000000000136c038 g     O .boot.preserved.data   0000000000000008 __stop_dma_ex_table
000000000136c08c g     O .boot.preserved.data   0000000000000004 zlib_dfltcc_support
000000000136c008 g     O .boot.preserved.data   0000000000000008 __edma
000000000136c028 g     O .boot.preserved.data   0000000000000008 __start_dma_ex_table
000000000136c018 g     O .boot.preserved.data   0000000000000008 __kaslr_offset
000000000136c078 g     O .boot.preserved.data   0000000000000008 ipl_cert_list_size
000000000136c084 g     O .boot.preserved.data   0000000000000004 ipl_secure_flag
000000000136c080 g     O .boot.preserved.data   0000000000000004 ipl_block_valid
000000000136c000 g     O .boot.preserved.data   0000000000000008 __diag210_tmp_dma
000000000136c088 g     O .boot.preserved.data   0000000000000004 prot_virt_guest
000000000136c048 g     O .boot.preserved.data   0000000000000028 diag_dma_ops
000000000136c030 g     O .boot.preserved.data   0000000000000008 __stext_dma
000000000136c010 g     O .boot.preserved.data   0000000000000008 __etext_dma
000000000136c090 g       .boot.preserved.data   0000000000000000 __boot_data_preserved_end
000000000136c070 g     O .boot.preserved.data   0000000000000008 ipl_cert_list_addr

$ llvm-objdump -t -j .boot.preserved.data out.s390/vmlinux

out.s390/vmlinux:       file format ELF64-s390

SYMBOL TABLE:
0000000000100000 l    d  .text  00000000 .text
0000000000ea6000 l    d  .rodata        00000000 .rodata
000000000112ae94 l    d  .interp        00000000 .interp
000000000112aea3 l    d  .dynstr        00000000 .dynstr
0000000001138708 l    d  .hash  00000000 .hash
0000000001141098 l    d  .gnu.hash      00000000 .gnu.hash
...
llvm-objdump: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file

cc @rupprecht

[nathanchance]

This comes from arch/s390/boot/Makefile, where it is doing some section comparisons to make sure that they match: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/s390/boot/Makefile#n48

[nathanchance]

The warnings are still present but the build does not error:

$ make -skj"$(nproc)" ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- LD=s390x-linux-gnu-ld LLVM=1 OBJCOPY=s390x-linux-gnu-objcopy defconfig all
...
llvm-objdump: warning: section '.boot.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump: warning: section '.boot.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file
...

Might mean the check might not be working properly?

[nickdesaulniers]

Does the error string "error: section $* differs between $< and $(word 2,$^)" print and show which object files are being compared?

[rupprecht]

I'm not sure what the original error was. The warning seems benign (should not be firing) but should be fixed. Filed as http://llvm.org/PR50085.

It looks like the warning for -j only fires correctly for certain flags. We keep track of which sections we "see" in different flags (e.g. -h), but for -t, we print the symbol table, we don't iterate over any sections -- so in a sense we never "saw" any sections, and by extension, we never saw the .boot.data sections, hence the (erroneous) warning.

More minimal repro:

$ bin/clang -xc -c /dev/null -o /tmp/null.o
$ bin/llvm-objdump -j .text -h /tmp/null.o  # -j and -h work fine

/tmp/null.o:    file format elf64-x86-64

Sections:
Idx Name          Size     VMA              Type
  2 .text         00000000 0000000000000000 TEXT
$ bin/llvm-objdump -j .text -t /tmp/null.o  # -j and -t don't work fine

/tmp/null.o:    file format elf64-x86-64

SYMBOL TABLE:
0000000000000000 l    df *ABS*  0000000000000000 null
bin/llvm-objdump: warning: section '.text' mentioned in a -j/--section option, but not found in any input file

However, GNU objdump prints the same warning for my minimal repro above. And it looks like you don't see the warning with s390x-linux-gnu-objdump? Strange...

[nickdesaulniers]

So I still see these warnings with llvm-objcopy-18, but I no longer see the error+build failure.

...
$ make LLVM=1 ARCH=s390 LD=s390x-linux-gnu-ld.bfd OBJCOPY=s390x-linux-gnu-objcopy -j128 all
  SECTCMP .boot.preserved.data
llvm-objdump: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump: warning: section '.boot.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump: warning: section '.boot.preserved.data' mentioned in a -j/--section option, but not found in any input file
llvm-objdump: warning: section '.boot.data' mentioned in a -j/--section option, but not found in any input file
  OBJCOPY arch/s390/boot/bzImage
$ echo $?
0