[libcxx-commits] [PATCH] D119969: [libc++] Unconditionally provide the ability for users to enable assertions

[Dimitry Andric via Phabricator via libcxx-commits]

dim added subscribers: emaste, dim.
dim added a comment.

In D119969#3351389 <https://reviews.llvm.org/D119969#3351389>, @ldionne wrote:

> In D119969#3349883 <https://reviews.llvm.org/D119969#3349883>, @manojgupta wrote:
>
>> Running readelf shows following in our shipping shared libs.
>>
>>    231: 00000000000c7db0     8 OBJECT  GLOBAL DEFAULT   23 _ZNSt3__123__libcpp_debug_functionE
>>    668: 0000000000075160    13 FUNC    GLOBAL DEFAULT   14 _ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE
>>   1438: 0000000000075110    79 FUNC    GLOBAL DEFAULT   14 _ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE
>>   1979: 0000000000074ef0   544 FUNC    GLOBAL DEFAULT   14 _ZNKSt3__119__libcpp_debug_info4whatEv
>
> Okay, right -- so as expected, you've been shipping support for the debug mode as part of the dylib, and if any user has been enabling assertions with `_LIBCPP_DEBUG=0`, they are relying on those symbols. So I think my proposed direction stands (it's this patch as-is). It's not the most elegant design since we're reusing old `__libcpp_debug_foo` for assertions, but I think it's the best decision engineering-wise for the time being.

We've got something similar on FreeBSD:

  % readelf -aW /lib/libc++.so.1
  ...
  Relocation section '.rela.dyn' at offset 0x354f8 contains 2161 entries:
  ...
  00000000000fc6e0  0000012c00000001 R_X86_64_64            0000000000092f60 std::__1::__libcpp_abort_debug_function(std::__1::__libcpp_debug_info const&) + 0
  00000000000fb130  0000019b00000006 R_X86_64_GLOB_DAT      00000000000fc6e0 std::__1::__libcpp_debug_function + 0
  ...
  Relocation section '.rela.plt' at offset 0x41f90 contains 572 entries:
  ...
  00000000000fca38  0000085700000007 R_X86_64_JUMP_SLOT     0000000000092d10 std::__1::__libcpp_debug_info::what() const + 0
  ...
  Symbol table '.dynsym' contains 2398 entries:
  ...
     300: 0000000000092f60    82 FUNC    GLOBAL DEFAULT   14 std::__1::__libcpp_abort_debug_function(std::__1::__libcpp_debug_info const&)
     411: 00000000000fc6e0     8 OBJECT  GLOBAL DEFAULT   25 std::__1::__libcpp_debug_function
    1468: 0000000000092fc0    18 FUNC    GLOBAL DEFAULT   14 std::__1::__libcpp_set_debug_function(void (*)(std::__1::__libcpp_debug_info const&))
    2135: 0000000000092d10   586 FUNC    GLOBAL DEFAULT   14 std::__1::__libcpp_debug_info::what() const

These all originate in `debug.cpp`. I think we have been shipping it like this since we switched from libstd++ to libc++ years ago.

So this change is fine from our perspective.


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D119969