This is a follow up to https://reviews.llvm.org/D104080, and ca3bdb57fa (diff-e64a48fabe31db213a631fdc5f2acb51bdddf3f16a8fb2928784f4c579229585). The implementation of call graph profile was changed from a black box section to relocation approach. This was done to be compatible with post processing tools like strip/objcopy, and llvm equivalent. When they are invoked on object file before the final linking step with this new approach the symbol indices correctness is preserved.
The GNU binutils tools change the REL section to RELA section, unlike llvm tools. For example when strip -S is run on the ELF object files, as an intermediate step before linking. To preserve compatibility this patch extends implementation in LLD and ELFDumper to support both REL and RELA sections for call graph profile.
Reviewed By: MaskRay, jhenderson
Differential Revision: https://reviews.llvm.org/D105217
... even on targets preferring RELA. The section is only consumed by ld.lld
which can handle REL.
Follow-up to D104080 as I explained in the review. There are two advantages:
* The D104080 code only handles RELA, so arm/i386/mips32 etc may warn for -fprofile-use=/-fprofile-sample-use= usage.
* Decrease object file size for RELA targets
While here, change the relocation to relocate weights, instead of 0,1,2,3,..
I failed to catch the issue during review.
Currently when .llvm.call-graph-profile is created by llvm it explicitly encodes the symbol indices. This section is basically a black box for post processing tools. For example, if we run strip -s on the object files the symbol table changes, but indices in that section do not. In non-visible behavior indices point to wrong symbols. The visible behavior indices point outside of Symbol table: "invalid symbol index".
This patch changes the format by using R_*_NONE relocations to indicate the from/to symbols. The Frequency (Weight) will still be in the .llvm.call-graph-profile, but symbol information will be in relocation section. In LLD information from both sections is used to reconstruct call graph profile. Relocations themselves will never be applied.
With this approach post processing tools that handle relocations correctly work for this section also. Tools can add/remove symbols and as long as they handle relocation sections with this approach information stays correct.
Doing a quick experiment with clang-13.
The size went up from 107KB to 322KB, aggregate of all the input sections. Size of clang-13 binary is ~118MB. For users of -fprofile-use/-fprofile-sample-use the size of object files will go up slightly, it will not impact final binary size.
Reviewed By: jhenderson, MaskRay
Differential Revision: https://reviews.llvm.org/D104080
Currently, `ELFFile<ELFT>::getEntry` does not check an index of
an entry. Because of that the code might read past the end of the symbol
table silently. I've added a test to `llvm-readobj\ELF\relocations.test`
to demonstrate the possible issue. Also, I've added a unit test for
this method.
After this change, `getEntry` stops reporting the section index and
reuses the `getSectionContentsAsArray` method, which already has
all the validation needed. Our related warnings now provide
more and better context sometimes.
Differential revision: https://reviews.llvm.org/D93209
Currently we have to set 'Machine' to something in our
YAML descriptions. Usually we use 'EM_X86_64' for 64-bit targets
and 'EM_386' for 32-bit targets. At the same time, in fact, in most
cases our tests do not need a machine type and we can use
'EM_NONE'.
This is cleaner, because avoids the need of using a particular machine.
In this patch I've made the 'Machine' key optional (the default value,
when it is not specified is `EM_NONE`) and removed it (where possible)
from yaml2obj, obj2yaml and llvm-readobj tests.
There are few tests left where I decided not to remove it, because
I didn't want to touch CHECK lines or doing anything more complex
than a removing a "Machine: *" line and formatting lines around.
Differential revision: https://reviews.llvm.org/D86202
This patch does the following:
1) Starts using YAML macro to reduce the number of YAML documents in tests.
2) Adds `#` before 'RUN'/`CHECK` lines in a few tests where it is missing.
3) Removes unused YAML keys.
4) Starts using `ENTSIZE=<none>` to simplify tests (see D84526).
5) Removes trailing white spaces in a few places.
Differential revision: https://reviews.llvm.org/D85013
The code we have currently reports an error if something is not right with the
profile section. Instead we can report a warning and continue dumping when it is possible.
This patch does it.
Differential revision: https://reviews.llvm.org/D83129
Summary: Rename --elf-cg-profile to --cg-profile and keep --elf-cg-profile as an alias of --cg-profile.
Reviewers: jhenderson, MaskRay, espindola, hans
Reviewed By: jhenderson, MaskRay
Subscribers: emaste, rupprecht, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D81855
This adds a test to document --elf-cg-profile option we have.
I am going to refactor this area, and this patch is mostly to
create a base for a follow-up change.
Differential revision: https://reviews.llvm.org/D74115
Alexander Yermolovich