[lldb-dev] LLDB Evolution - Final Form

Zachary Turner via lldb-dev lldb-dev at lists.llvm.org
Tue Sep 20 13:45:24 PDT 2016

I do agree that asserts are sometimes used improperly.  But who's to say
that the bug was the assert, and not the surrounding code?  For example,
consider this code:

int x = *p;

Should this assert also not be here in library code?  I mean it's obvious
that the program is about to crash if p is invalid.  Asserts should mean
"you're about to invoke undefined behavior", and a crash is *better* than
undefined behavior.  It surfaces the problem so that you can't let it slip
under the radar, and it also alerts you to the point that the UB is
invoked, rather than later.

What about this assert?

int x = strlen(ptr);

Surely that assert is ok right?  Do we need to check whether ptr is valid
EVERY SINGLE TIME we invoke strlen, or any other function for that matter?
The code would be a disastrous mess.

If you think you've found an improper assert, the thing to do is raise it
on the proper mailing list and present your case of why you think it's an
improper assert.  asserting is not inherently wrong, but like anything, you
have to use it right.

On Tue, Sep 20, 2016 at 1:37 PM Ted Woodward <ted.woodward at codeaurora.org>

> From: lldb-dev [mailto:lldb-dev-bounces at lists.llvm.org] On Behalf Of
> Zachary Turner via lldb-dev
> Sent: Tuesday, September 20, 2016 12:47 PM
> > This kind of philisophical debate is probably worthy of a separate
> thread :)  That being said, I think asserts are typically used in places
> where the assert firing means "You're going to crash *anyway*"
> This is emphatically NOT the case.
> One of the first tasks I was given when I started at Qualcomm was to fix
> the disassembler for Hexagon. It was a mess - it would assert if the
> disassembly tables couldn't identify an opcode. Maybe that's fine for an
> assembler, assert if you can't generate an opcode, but an unidentified
> opcode should print a warning and move on. It's not a fatal error to
> disassemble data!
> There are other instances of this in llvm. I agree with Greg - libraries
> shouldn't assert.  Send an error back to the caller, and let the caller
> handle it. A typo in my expression that lldb sends to clang shouldn't crash
> my debug session.
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
> Linux Foundation Collaborative Project
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