llvm::errs() doesn't do anything in release builds on Linux, in libdxcompiler.so

[dneto0]

Description

I generally use Linux to develop DXC.
When I debug issues in the compiler, I often use llvm::errs().
Unfortunately, llvm::errs() doesn't do anything on release builds in Linux, when I use libdxcompiler.so

I've tried tracing through but haven't found the reason.

Steps to Reproduce

Build libdxcompiler.so on Linux.
(I'll fill in details below)

Actual Behavior

doesn't print.

Environment

DXC git d915232

[dneto0]

Seeing as this only affects libdxcompiler.so this might be on our end?

[dneto0]

Update. It affects Linux release builds when:

• using libdxcompiler.so
• or the command line compiler dxc when it traps. (ok, that's my fault due to Add CMake option DXC_CODEGEN_EXCEPTIONS_TRAP #6764, so I'll take responsibility for that.)

[llvm-beanz]

I suspect what you’re seeing here is that dxcompiler reroutes llvm::errs to an output stream that is surfaced through the API as DXC_OUT_ERRORS:

DirectXShaderCompiler/include/dxc/dxcapi.h

Line 727 in a54abe8

DXC_OUT_ERRORS = 2, ///< IDxcBlobUtf8 or IDxcBlobWide.

That allows the caller to control where the output gets printed to, and observes the general best practice of not having shared libraries write to stdout or stderr.

[damyanp]

@llvm-beanz / @dneto0 - is there work remaining for this issue?

[damyanp]

@dneto0 - if we, or you, need to do something here then please feel free to reopen.