[PATCH] D27041: [ELF] - Disable emiting multiple output sections when merging is disabled.

[George Rimar via llvm-commits]

grimar added a comment.

In https://reviews.llvm.org/D27041#604490, @ruiu wrote:

> I think I do not understand what this patch is trying to address. Did you mean that FreeBSD EFI loader passes -O0 to linker?


No it doesn't. My point is next:

For linkerscript we take "M" and "S" flags in account:

  uintX_t Flags = C->Flags & (SHF_MERGE | SHF_STRINGS);

That is done because currently our implementation requires one output section per "kind",
what is different from what gnu linkers do.

With -O0 sections metging is disabled:

  bool elf::ObjectFile<ELFT>::shouldMerge(const Elf_Shdr &Sec) {
    if (Config->Optimize == 0)
      return false;

In that case there is no point to create more output sections, we can combine them as regular into single section.
Currently that is the only way to get output similar to ld/gold. And currently that way broken.

Returning o EFI loader. Change above is useful for investigation of broken files, including the loader.
Currently LLD output for loader is:

  [ 4] .data             PROGBITS         0000000000058000  00059000
        0000000000006355  0000000000000001 AMS       0     0     1
   [ 5] .got              PROGBITS         0000000000068520  0005f520
        00000000000004a0  0000000000000000  WA       0     0     8
   [ 6] .data             PROGBITS         000000000005e360  00055360
        000000000000a142  0000000000000000  WA       0     0     16
   [ 7] .data             PROGBITS         00000000000684b0  0005f4b0
        0000000000000051  0000000000000001 AMS       0     0     16
   [ 8] .data             PROGBITS         0000000000068502  0005f502
        0000000000000016  0000000000000002 AMS       0     0     2
   [ 9] .data             PROGBITS         0000000000068518  0005f518

.got inside .data is fixed by https://reviews.llvm.org/D27040, but there are still multiple .data sections.
That might be a problem and might be not. It is unclear now if EFI firmware
accepts file with multiple data or if we can have any other problems at other points like
if objcopy fine to convert this to EFI PE format.

So I believe the behavior of this patch is:

1. Fixes bug in output (no need to produce more sections that we can and take in account flags that are unused).
2. Might be helpfull for investigation such issues like above in FreeBSD at least.




https://reviews.llvm.org/D27041