[tor-bugs] #23357 [Core Tor/Tor]: Build with non-Cross-DSO CFI

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#23357: Build with non-Cross-DSO CFI
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 Reporter:  shawn.webb                  |          Owner:  (none)
     Type:  enhancement                 |         Status:  needs_revision
 Priority:  Medium                      |      Milestone:  Tor:
                                        |  0.3.2.x-final
Component:  Core Tor/Tor                |        Version:
 Severity:  Normal                      |     Resolution:
 Keywords:  security, defence-in-depth  |  Actual Points:
Parent ID:                              |         Points:  1.0
 Reviewer:                              |        Sponsor:
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Comment (by shawn.webb):

 > When we configure with a recent clang/llvm and --enable-cfi, then
 compile .o files and link them together into the tor binary, does non-
 Cross-DSO CFI work for that binary?

 Yup. One problem with trying to use CFI with both static and dynamic
 libraries is that you need to use llvm-ar, llvm-nm, and llvm-objdump as
 your ar, nm, and objdump applications. This is because compiling with CFI
 will cause clang to output intermediate object files as LLVM bitcode files
 instead of ELF object files. The ar, nm, and objdump applications that
 come on most (all?) operating systems only support ELF. Essentially, the
 whole compiler toolchain must be switched over to the entire llvm tool
 suite.

 So, what I can do, is expand the patch to apply the CFLAGS and LDFLAGS to
 more of the applications (rather than just tor). This way, we skip
 applying CFI to the library code (even though the libraries in the
 codebase get statically linked).

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23357#comment:11>
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